Nutrition and Athletic
Performance
ABSTRACT
It is the position of the Academy of Nutrition and Dietetics, Dietitians of
Canada, and the American College of Sports Medicine that the performance
of, and recovery from, sporting activities are enhanced by well-chosen nutrition
strategies. These organizations provide guidelines for the appropriate
type, amount, and timing of intake of food, fluids, and supplements to
promote optimal health and performance across different scenarios of
training and competitive sport. This position paper was prepared for members
of the Academy of Nutrition and Dietetics, Dietitians of Canada (DC),
and American College of Sports Medicine (ACSM), other professional associations,
government agencies, industry, and the public. It outlines the
Academy_s, DC_s and ACSM_s stance on nutrition factors that have been
determined to influence athletic performance and emerging trends in the
field of sports nutrition. Athletes should be referred to a registered dietitian/
nutritionist for a personalized nutrition plan. In the United States and in
Canada, the Certified Specialist in Sports Dietetics (CSSD) is a registered
dietitian/nutritionist and a credentialed sports nutrition expert.
POSITION STATEMENT
It is the position of the Academy of Nutrition and Dietetics,
Dietitians of Canada, and the American College of
Sports Medicine that the performance of, and recovery from,
sporting activities are enhanced by well-chosen nutrition
strategies. These organizations provide guidelines for the
appropriate type, amount and timing of intake of food, fluids
and dietary supplements to promote optimal health and
sport performance across different scenarios of training and
competitive sport.
This paper outlines the current energy, nutrient, and fluid
recommendations for active adults and competitive athletes.
These general recommendations can be adjusted by sports
dietitians to accommodate the unique issues of individual
athletes regarding health, nutrient needs, performance goals,
physique characteristics (ie, body size, shape, growth, and
composition), practical challenges and food preferences. Since
credentialing practices vary internationally, the term ‘‘sports
dietitian’’ will be used throughout this paper to encompass all
terms of accreditation, including RDN, RD, CSSD, or PDt.
This Academy position paper includes the authors_ independent
review of the literature in addition to systematic
review conducted using the Academy_s Evidence Analysis
Process and information from the Academy Evidence
Analysis Library (EAL). Topics from the EAL are clearly
delineated. The use of an evidence-based approach provides
important added benefits to earlier review methods. The
major advantage of the approach is the more rigorous standardization
of review criteria, which minimizes the likelihood
of reviewer bias and increases the ease with which
disparate articles may be compared. For a detailed description
of the methods used in the evidence analysis process,
access the Academy_s Evidence Analysis Process at https://
www.andevidencelibrary.com/eaprocess.
Conclusion Statements are assigned a grade by an expert
work group based on the systematic analysis and evaluation
of the supporting research evidence. Grade I = Good; Grade
II = Fair; Grade III = Limited; Grade IV = Expert Opinion
Only; and Grade V = Not Assignable (because there is no
evidence to support or refute the conclusion). See grade
definitions at www.andevidencelibrary.com/.
Evidence-based information for this and other topics can be
found at https://www.andevidencelibrary.com and subscriptions
for non-members are purchasable at https://
www.andevidencelibrary.com/store.cfm.
EVIDENCE-BASED ANALYSIS
This paper was developed using the Academy of Nutrition
and Dietetics Evidence Analysis Library (EAL) and will outline
some key themes related to nutrition and athletic performance.
The EAL is a synthesis of relevant nutritional research on important
dietetic practice questions. The publication range for
SPECIAL COMMUNICATIONS
This joint position statement is authored by the Academy of Nutrition and
Dietetics (AND), Dietitians of Canada (DC), and American College of
Sports Medicine (ACSM). The content appears in AND style. This paper is
being published concurrently in Medicine & Science in Sports & ExerciseÒ
and in the Journal of the Academy of Nutrition and Dietetics, and the
Canadian Journal of Dietetic Practice and Research. Individual name recognition
is reflected in the acknowledgments at the end of the statement.
Submitted for publication December 2015.
Accepted for publication December 2015.
0195-9131/16/4803-0543/0
MEDICINE & SCIENCE IN SPORTS & EXERCISEÒ
Copyright Ó 2016 by the American College of Sports Medicine, Academy
of Nutrition and Dietetics, and Dietitians of Canada
DOI: 10.1249/MSS.0000000000000852
ACADEMY OF NUTRITION AND DIETETICS
DIETITIANS OF CANADA
JOINT POSITION STATEMENT
543
Copyright © 2016 by the American College of Sports Medicine. Unauthorized reproduction of this article is prohibited.
the evidence-based analysis spanned March 2006–November
2014. For the details on the systematic review and methodology
go to www.andevidencelibrary.com. Table 1 presents the
evidence analysis questions used in this position paper.
NEW PERSPECTIVES IN SPORTS NUTRITION
The past decade has seen an increase in the number and
topics of publications of original research and review, consensus
statements from sporting organizations, and opportunities
for qualification and accreditation related to sports nutrition
and dietetics. This bears witness to sports nutrition as a
dynamic area of science and practice that continues to flourish
in both the scope of support it offers to athletes and the
strength of evidence that underpins its guidelines. Before
embarking on a discussion of individual topics, it is valuable
to identify a range of themes in contemporary sports nutrition
that corroborate and unify the recommendations in
this paper.
1. Nutrition goals and requirements are not static. Athletes
undertake a periodized program in which preparation for
peak performance in targeted events is achieved by
integrating different types of workouts in the various
TABLE 1. Evidence analysis questions included in the position statement Refer to http://www.andevidencelibrary.com/ for a complete list of evidence analysis citations.
EAL Question Conclusion and Evidence Grade
Energy Balance and Body Composition
#1: In adult athletes, what effect does negative energy balance have on exercise
performance?
In three out of six studies of male and female athletes, negative energy balance (losses of
0.02% to 5.8% body mass; over five 30-day periods) was not associated with decreased
performance. In the remaining three studies where decrements in both anaerobic and aerobic
performance were observed, slow rates of weight loss (0.7% reduction body mass) were
more beneficial to performance compared to fast (1.4% reduction body mass) and one study
showed that self-selected energy restriction resulted in decreased hormone levels.
Grade II- Fair
#2: In adult athletes, what is the time, energy, and macronutrient requirement
to gain lean body mass?
Over periods of 4 to 12 weeks, increasing protein intake during hypocaloric conditions maintains
lean body mass in male and female resistance-trained athletes. When adequate energy is
provided or weight loss is gradual, an increase in lean body mass may be observed.
Grade III- Limited
Recovery
#3: In adult athletes, what is the effect of consuming carbohydrate on
carbohydrate and protein-specific metabolic responses and/or exercise
performance during recovery?
Based on the limited evidence available, there were no clear effects of carbohydrate
supplementation during and after endurance exercise on carbohydrate and protein-specific
metabolic responses during recovery.
Grade III- Limited
#4: What is the effect of consuming CHO on exercise performance during
recovery?
Based on the limited evidence available, there were no clear effects of carbohydrate
supplementation during and after endurance exercise on endurance performance in adult
athletes during recovery.
Grade III- Limited
#5: In adult athletes, what is the effect of consuming carbohydrate and protein
together on carbohydrate and protein-specific metabolic responses
during recovery?
 Compared to ingestion of carbohydrate alone, coingestion of carbohydrate plus protein
together during the recovery period resulted in no difference in the rate of muscle
glycogen synthesis.
 Coingestion of protein with carbohydrate during the recovery period resulted in improved net
protein balance post-exercise.
 The effect of co-ingestion of protein with carbohydrate on creatine kinase levels is
inconclusive and shows no impact on muscle soreness post-exercise.
Grade I- Good
#6: In adult athletes, what is the effect of consuming carbohydrate and protein
together on carbohydrate and protein-specific metabolic responses
during recovery?
Co-ingestion of carbohydrate plus protein, together during the recovery period resulted in no
clear influence on subsequent strength or sprint power.
Grade II- Fair
#7: In adult athletes, what is the effect of consuming carbohydrate and protein
together on exercise performance during recovery?
Ingesting protein during the recovery period (post-exercise) led to accelerated recovery of static
force and dynamic power production during the delayed onset muscle soreness period and
more repetitions performed subsequent to intense resistance training.
Grade II- Fair
#8: In adult athletes, what is the effect of consuming protein on carbohydrate
and protein-specific metabolic responses during recovery?
Ingesting protein (approximately 20 g to 30 g total protein, or approximately 10 g of essential
amino acids) during exercise or the recovery period (post-exercise) led to increased whole
body and muscle protein synthesis as well as improved nitrogen balance.
Grade I- Good
Training
#9: In adult athletes, what is the optimal blend of carbohydrates for maximal
carbohydrate oxidation during exercise?
Based on the limited evidence available, carbohydrate oxidation was greater in carbohydrate
conditions (glucose and glucose + fructose) compared to water placebo, but no differences
between the two carbohydrate blends tested were observed in male cyclists. Exogenous
carbohydrate oxidation was greater in the glucose + fructose condition vs. glucose-only in
a single study.
Grade III- Limited
#10: In adult athletes, what effect does training with limited carbohydrate
availability have on metabolic adaptations that lead to performance
improvements?
Training with limited carbohydrate availability may lead to some metabolic adaptations during
training, but did not lead to performance improvements. Based on the evidence examined,
while there is insufficient evidence supporting a clear performance effect, training with
limited carbohydrate availability impaired training intensity and duration.
Grade II- Fair
#11: In adult athletes, what effect does consuming high or low glycemic
meals or foods have on training related metabolic responses and
exercise performance?
In the majority of studies examined, neither glycemic index nor glycemic load affected
endurance performance nor metabolic responses when conditions were matched for
carbohydrate and energy.
Grade I- Good
Evidence Grades: Grade I: Good; Grade II: Fair; Grade III: Limited; Grade IV: Expert Opinion Only; Grade V: Not Assignable.
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Copyright © 2016 by the American College of Sports Medicine. Unauthorized reproduction of this article is prohibited.
cycles of the training calendar. Nutrition support also
needs to be periodized, taking into account the needs
of daily training sessions (which can range from
minor in the case of ‘‘easy’’ workouts to substantial
in the case of high quality sessions (eg, high intensity,
strenuous, or highly skilled workouts) and
overall nutritional goals.
2. Nutrition plans need to be personalized to the individual
athlete to take into account the specificity and
uniqueness of the event, performance goals, practical
challenges, food preferences, and responses to various
strategies.
3. A key goal of training is to adapt the body to develop
metabolic efficiency and flexibility while competition
nutrition strategies focus on providing adequate substrate
stores to meet the fuel demands of the event and
support cognitive function.
4. Energy availability, which considers energy intake in
relation to the energy cost of exercise, sets an important
foundation for health and the success of sports
nutrition strategies.
5. The achievement of the body composition associated
with optimal performance is now recognized as an
important but challenging goal that needs to be individualized
and periodized. Care should be taken to
preserve health and long term performance by avoiding
practices that create unacceptably low energy availability
and psychological stress.
6. Training and nutrition have a strong interaction in
acclimating the body to develop functional and metabolic
adaptations. Although optimal performance is
underpinned by the provision of pro-active nutrition
support, training adaptations may be enhanced in the
absence of such support.
7. Some nutrients (eg, energy, carbohydrate, and protein)
should be expressed using guidelines per kg
body mass to allow recommendations to be scaled to
the large range in the body sizes of athletes. Sports
nutrition guidelines should also consider the importance
of the timing of nutrient intake and nutritional
support over the day and in relation to sport rather
than general daily targets.
8. Highly trained athletes walk a tightrope between
training hard enough to achieve a maximal training
stimulus and avoiding the illness and injury risk associated
with an excessive training volume.
9. Competition nutrition should target specific strategies
that reduce or delay factors that would otherwise
cause fatigue in an event; these are specific to the
event, the environment/scenario in which it is undertaken,
and the individual athlete.
10. New performance nutrition options have emerged in
the light of developing but robust evidence that brain
sensing of the presence of carbohydrate, and potentially
other nutritional components, in the oral cavity
can enhance perceptions of well-being and increase
self-chosen work rates. Such findings present opportunities
for intake during shorter events, in which
fluid or food intake was previously not considered to
offer a metabolic advantage, by enhancing performance
via a central effect.
11. A pragmatic approach to advice regarding the use of
supplements and sports foods is needed in the face of
the high prevalence of interest in, and use by, athletes
and the evidence that some products can usefully
contribute to a sports nutrition plan and/or directly
enhance performance. Athletes should be assisted to
undertake a cost-benefit analysis of the use of such
products and to recognize that they are of the greatest
value when added to a well-chosen eating plan.
THEME 1: NUTRITION FOR
ATHLETE PREPARATION
Energy Requirements, Energy Balance
and Energy Availability
An appropriate energy intake is the cornerstone of the
athlete_s diet since it supports optimal body function, determines
the capacity for intake of macronutrient and
micronutrients, and assists in manipulating body composition.
An athlete_s energy intake from food, fluids and supplements
can be derived from weighed/measured food
records (typically 3–7 day), a multi-pass 24-hour recall or
from food frequency questionnaires.1
There are inherent limitations
with all of these methods, with a bias to the underreporting
of intakes. Extensive education regarding the
purpose and protocols of documenting intakes may assist
with compliance and enhance the accuracy and validity of
self-reported information.
Meanwhile an athlete_s energy requirements depend on the
periodized training and competition cycle, and will vary from
day to day throughout the yearly training plan relative to
changes in training volume and intensity. Factors that increase
energy needs above normal baseline levels include exposure to
cold or heat, fear, stress, high altitude exposure, some physical
injuries, specific drugs or medications (eg, caffeine, nicotine),
increases in fat-free mass and, possibly, the luteal phase of the
menstrual cycle.2
Aside from reductions in training, energy
requirements are lowered by aging, decreases in fat free mass
(FFM), and, possibly, the follicular phase of the menstrual
cycle.3
Energy balance occurs when total Energy Intake (EI)
equals Total Energy Expenditure (TEE), which in turn
consists of the summation of basal metabolic rate (BMR),
the Thermic Effect of Food (TEF) and the Thermic Effect of
Activity (TEA).
TEE ¼ BMR þ TEF þ TEA
TEA ¼ PlannedExerciseExpenditure þ SpontaneousPhysicalActivity
þ Non<ExerciseActivityThermogenesis
Techniques used to measure or estimate components of
TEE in sedentary and moderately active populations can
NUTRITION AND ATHLETIC PERFORMANCE Medicine & Science in Sports & Exercised 545
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also be applied to athletes, but there are some limitations to
this approach, particularly in highly competitive athletes.
Since the measurement of BMR requires subjects to remain
exclusively at rest, it is more practical to measure resting
metabolic rate (RMR) which may be 10% higher. Although
population-specific regression equations are encouraged, a
reasonable estimate of BMR can be obtained using either the
Cunningham4
or the Harris-Benedict5
equations, with an
appropriate activity factor being applied to estimate TEE.
Whereas RMR represents 60%–80% of TEE for sedentary
individuals, it may be as little as 38%–47% of TEE for elite
endurance athletes who may have a TEA as high as 50%
of TEE.2
TEA includes planned exercise expenditure, spontaneous
physical activity (eg, fidgeting), and non-exercise activity
thermogenesis. Energy expenditure from exercise (EEE) can
be estimated in several ways from activity logs (1–7 days
duration) with subjective estimates of exercise intensity
using activity codes and metabolic equivalents (METs),6,7
2015 US dietary guidelines8
and the Dietary Reference
Intakes (DRIs).9
The latter two typically underestimate the
requirements of athletes since they fail to cover the range in
body size or activity levels of competitive populations. Energy
availability (EA) is a concept of recent currency in sports nutrition,
which equates energy intake with requirements for
optimal health and function rather than energy balance. EA,
defined as dietary intake minus exercise energy expenditure
normalized to FFM, is the amount of energy available to the
body to perform all other functions after the cost of exercise
is subtracted.10
The concept was first studied in females,
where an EA of 45 kcal/kg FFM/d was found to be associated
with energy balance and optimal health; meanwhile,
a chronic reduction in EA, (particularly below 30 kcal/kg
FFM/d) was associated with impairments of a variety of body
functions.10
Low EA may occur from insufficient EI, high
TEE or a combination of the two. It may be associated with
disordered eating, a misguided or excessively rapid program
for loss of body mass, or inadvertent failure to meet energy
requirements during a period of high-volume training or
competition.10
Example Calculation of Energy Availability (EA):
60 kg body weight (BW), 20% BF, 80% FFM
(=48.0 kg FFM), EI = 2400 kcal/d, EEE = 500 kcal/d
EA = (EI – EEE) / FFM = (2400 – 500) kcal/d / 48.0 kg =
39.6 kcal/kg FFM/d
The concept of EA emerged from the study of Female
Athlete Triad (Triad), which started as a recognition of the
interrelatedness of clinical issues with disordered eating,
menstrual dysfunction, and low bone mineral density in female
athletes and then evolved into a broader understanding
of the concerns associated with any movement along the
spectra away from optimal energy availability, menstrual
status, and bone health.11
Although not embedded in the
Triad spectrum, it is recognized that other physiological
consequences may result from one of the components of the
Triad in female athletes, such as endocrine, gastrointestinal,
renal, neuro-psychiatric, musculoskeletal, and cardiovascular
dysfunction.11
Indeed, an extension of the Triad has been
proposed, Relative Energy Deficiency in Sport (RED-S), as
an inclusive description of the entire cluster of physiological
complications observed in male and female athletes who
consume energy intakes that are insufficient in meeting the
needs for optimal body function once the energy cost of exercise
has been removed.12
Specifically, health consequences
of RED-S may negatively affect menstrual function, bone
health, endocrine, metabolic, hematological, growth and development,
psychological, cardiovascular, gastrointestinal,
and immunological systems. Potential performance effects of
RED-S may include decreased endurance, increased injury
risk, decreased training response, impaired judgment, decreased
coordination, decreased concentration, irritability,
depression, decreased glycogen stores, and decreased muscle
strength.12
It is now also recognized that impairments of
health and function occur across the continuum of reductions
in EA, rather than occurring uniformly at an EA threshold,
and require further research.12
It should be appreciated that
low EA is not synonymous with negative EB or weight loss;
indeed, if a reduction in EA is associated with a reduction in
RMR, it may produce a new steady-state of EB or weight
stability at a lowered energy intake that is insufficient to
provide for healthy body function.
Regardless of the terminology, it is apparent that low EA
in male and female athletes may compromise athletic performance
in the short and long-term. Screening and treatment
guidelines have been established for management of
low EA11,12
and should include assessment with the Eating
Disorder Inventory-3 resource13
or the DSM-5, which includes
changes in eating disorder criteria.14
There is evidence
that interventions to increase EA are successful in
reversing at least some impaired body functions; for example,
in a 6-month trial with female athletes experiencing
menstrual dysfunction, dietary treatment to increase EA to
~40 kcal/kg FFM/d resulted in resumption of menses in all
subjects in a mean of 2.6 months.6
Body Composition and Sports Performance
Various attributes of physique (body size, shape and
composition) are considered to contribute to success in various
sports. Of these, body mass (‘‘weight’’) and body composition
are often focal points for athletes since they are most
able to be manipulated. Although it is clear that the assessment
and manipulation of body composition may assist in the
progression of an athletic career, athletes, coaches, and
trainers should be reminded that athletic performance cannot
be accurately predicted solely based on body weight and
composition. A single and rigid ‘‘optimal’’ body composition
should not be recommended for any event or group of
http://www.acsm-msse.org546 Official Journal of the American College of Sports Medicine
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athletes.15
Nevertheless, there are relationships between body
composition and sports performance that are important to
consider within an athlete_s preparation.
In sports involving strength and power, athletes strive to
gain fat-free mass via a program of muscle hypertrophy at
specified times of the annual macro-cycle. Whereas some
athletes aim to gain absolute size and strength per se, in
other sports, in which the athlete must move their own body
mass or compete within weight divisions, it is important to
optimize power to weight ratios rather than absolute power.16
Thus, some power athletes also desire to achieve low body fat
levels. In sports involving weight divisions (eg. combat
sports, lightweight rowing, weightlifting), competitors typically
target the lowest achievable body weight category,
while maximizing their lean mass within this target.
Other athletes strive to maintain a low body mass and/or
body fat level for separate advantages.17
Distance runners
and cyclists benefit from a low energy cost of movement and
a favorable ratio of weight to surface area for heat dissipation.
Team athletes can increase their speed and agility by
being lean, while athletes in acrobatic sports (eg, diving.
gymnastics, dance) gain biomechanical advantages in being
able to move their bodies within a smaller space. In some of
these sports and others (eg, body building), there is an element
of aesthetics in determining performance outcomes.
Although there are demonstrated advantages to achieving a
certain body composition, athletes may feel pressure to
strive to achieve unrealistically low targets of weight/body
fat or to reach them in an unrealistic time frame.15
Such
athletes may be susceptible to practicing extreme weight
control behaviors or continuous dieting, exposing themselves
to chronic periods of low EA and poor nutrient support
in an effort to repeat previous success at a lower weight
or leaner body composition.15,18
Extreme methods of weight
control can be detrimental to health and performance, and
disordered eating patterns have also been observed in these
sport scenarios.15,18
Nevertheless, there are scenarios in which an athlete will
enhance their health and performance by reducing body
weight or body fat as part of a periodized strategy. Ideally,
this occurs within a program that gradually achieves an individualized
‘‘optimal’’ body composition over the athlete_s
athletic career, and allows weight and body fat to track
within a suitable range within the annual training cycle.18
The program should also include avoiding situations in
which athletes inadvertently gain excessive amounts of body
fat as a result of a sudden energy mismatch when energy
expenditure is abruptly reduced (eg, the off-season or injury).
In addition, athletes are warned against the sudden or
excessive gain in body fat which is part of the culture of
some sports where a high body mass is deemed useful
for performance. Although body mass index is not appropriate
as a body composition surrogate in athletes, a chronic
interest in gaining weight may put some athletes at risk
for an ‘‘obese’’ body mass index which may increase the risk
of meeting the criteria for metabolic syndrome.19
Sports
dietitians should be aware of sports that promote the attainment
of a large body mass and screen for metabolic
risk factors.19
Methodologies for body composition assessment.
Techniques used to assess athlete body composition
include dual energy x-ray absorptiometry (DXA), hydrodensitometry,
air displacement plethysmography, skinfold
measurements, and single and multi-frequency bioelectrical
impedance analysis. Although DXA is quick and noninvasive,
issues around cost, accessibility, and exposure to a
small radiation dose limit its utility, particularly for certain
populations.20
When undertaken according to standardized
protocols, DXA has the lowest standard error of
estimate while skinfold measures have the highest. Air displacement
plethysmography (BodPod, Life Measurement,
Inc., Concord, CA) provides an alternative method that is
quick and reliable, but may underestimate body fat by 2%–
3%.20
Skinfold measurement and other anthropometric data
serve as an excellent surrogate measure of adiposity and
muscularity when profiling composition changes in response
to training interventions.20
However, it should be noted
that the standardization of skinfold sites, measurement
techniques, and calipers vary around the world. Despite
some limitations, this technique remains a popular method
of choice due to convenience and cost, with information
being provided in absolute measures and compared with
sequential data from the individual athlete or, in a general
way, with normative data collected in the same way from
athlete populations.20,21
All body composition assessment techniques should
be scrutinized to ensure accuracy and reliability. Testing
should be conducted with the same calibrated equipment,
with a standardized protocol, and by technicians with known
test-retest reliability. Where population–specific prediction
equations are used, they should be cross-validated and reliable.
Athletes should be educated on the limitations associated
with body composition assessment and should strictly
follow pre-assessment protocols. These instructions which
include maintaining a consistent training volume, fasting
status, and hydration from test to test20
should be enforced to
avoid compromising the accuracy and reliability of body
composition measures.
Body composition should be determined within a sports
program according to a schedule that is appropriate to the
performance of the event, the practicality of undertaking
assessments, and the sensitivity of the athlete. There are
technical errors associated with all body composition techniques
that limit the usefulness of measurement for athlete
selection and performance prediction. In lieu of setting absolute
body composition goals or applying absolute criteria
to categorize groups of athletes, it is preferred that normative
data are provided in terms of ranges.21
Since body fat content
for an individual athlete will vary over the season and
over the athlete_s career, goals for body composition should
be set in terms of ranges that can be appropriately tracked at
critical times. When conducting such monitoring programs,
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it is important that the communication of results with
coaches, training staff, and athletes is undertaken with sensitivity,
that limitations in measurement technique are recognized,
and that care is taken to avoid promoting an
unhealthy obsession with body composition.17,18
Sports dietitians
have important opportunities to work with these
athletes to help promote a healthy body composition, and to
minimize their reliance on rapid-weight loss techniques and
other hazardous practices that may result in performance
decrements, loss of fat-free mass, and chronic health risks.
Many themes should be addressed and include the creation
of a culture and environment that values safe and long-term
approaches to management of body composition; modification
of rules or practices around selection and qualification
for weight classes;16,19,22
and programs that identify
disordered eating practices at an early stage for intervention,
and where necessary, removal from play.18
Principles of altering body composition and
weight. Athletes often need assistance in setting appropriate
short-term and long-term goals, understanding nutritional
practices that can safely and effectively increase
muscle mass or reduce body fat/weight, and integrating
these strategies into an eating plan that achieves other performance
nutrition goals. Frequent follow up with these
athletes may have long-term benefits including shepherding
the athlete through short-term goals and reducing reliance on
extreme techniques and fad diets/behaviors.
There is ample evidence in weight sensitive and weightmaking
sports that athletes frequently undertake rapid weight
loss strategies to gain a competitive advantage.20,23,24
However,
the resultant hypohydration (body water deficit), loss of
glycogen stores and lean mass, and other outcomes of pathological
behaviors (eg, purging, excessive training, starving)
can impair health and performance.18
Nevertheless, responsible
use of short-term, rapid weight loss techniques, when
indicated, is preferred over extreme and extended energy restriction
and suboptimal nutrition support.17
When actual loss
of body weight is required, it should be programmed to occur
in the base phase of training or well out from competition to
minimize loss of performance,25
and should be achieved with
techniques that maximize loss of body fat while preserving
muscle mass and other health goals. Such strategies include
achieving a slight energy deficit to achieve a slow rather than
rapid rate of loss and increasing dietary protein intake. In this
regard, the provision of a higher protein intake (2.3 vs 1 g/kg/d)
in a shorter-term (2 w), energy-restricted diet in athletes was
found to retain muscle mass while losing weight and body fat.26
Furthermore, fat-free mass and performance may be better
preserved in athletes who minimize weekly weight loss to
G1% per week. 25
An individualized diet and training prescription for
weight/fat loss should be based on assessment of goals,
present training and nutrition practices, past experiences,
and trial and error. Nevertheless, for most athletes, the
practical approach of decreasing energy intake by ~250–
500 kcal/d from their periodized energy needs, while either
maintaining or slightly increasing energy expenditure, can
achieve progress towards short-term body composition goals
over approximately 3–6 weeks. In some situations, additional
moderate aerobic training and close monitoring can be
useful.27
These strategies can be implemented to help augment
the diet-induced energy deficits without negatively
impacting recovery from sport-specific training. Arranging
the timing and content of meals to support training nutrition
goals and recovery may reduce fatigue during frequent
training sessions and may help optimize body composition
over time.18
Overall barriers to body composition management
include limited access to healthy food options, limited
skills or opportunity for food preparation, lack of daily
routine, and exposure to catering featuring unlimited portion
sizes and energy-dense foods. Such factors, particularly
found in association with the travel and communal living
experiences in the athlete lifestyle, can promote poor dietary
quality that thwarts progress and may lead to the pursuit of
quick fixes, acute dieting, and extreme weight loss practices.
EAL Question #1 (Table 1) examined the effect of negative
energy balance on sport performance, finding only
fair support for an impairment of physical capacity due to a
hypoenergetic diet in the currently examined scenarios.
However, few studies have investigated the overlay of
factors commonly seen in practice, including the interaction
of poor dietary quality, low carbohydrate availability, excessive
training, and acute dehydration on chronic energy
restriction. The challenge of detecting small but important
changes in sports performance is noted in all areas of sports
nutrition.28
EAL Question #2 summarizes the literature on
optimal timing, energy, and macronutrient characteristics of
a program supporting a gain in fat-free mass when in energy
deficit (Table 1). Again the literature is limited in
quantity and range to allow definitive recommendations to
be made, although there is support for the benefits of increased
protein intake.
Macronutrient Requirements for Sport
Energy pathways and training adaptations. Guidelines
for the timing and amount of intake of macronutrients in
the athlete_s diet should be underpinned by a fundamental
understanding of how training-nutrient interactions affect energy
systems, substrate availability and training adaptations.
Exercise is fueled by an integrated series of energy systems
which include non-oxidative (phosphagen and glycolytic) and
aerobic (fat and carbohydrate oxidation) pathways, using
substrates that are both endogenous and exogenous in origin.
Adenosine triphosphate and phosphocreatine (phosphagen
system) provide a rapidly available energy source for muscular
contraction, but not at sufficient levels to provide a continuous
supply of energy for longer than ~10 seconds. The
anaerobic glycolytic pathway rapidly metabolizes glucose and
muscle glycogen through the glycolytic cascade and is the
primary pathway supporting high-intensity exercise lasting
10–180 seconds. Since neither the phosphagen nor the
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glycolytic pathway can sustain energy demands to allow
muscles to contract at a very high rate for longer lasting
events, oxidative pathways provide the primary fuels for
events lasting longer than ~2 minutes. The major substrates
include muscle and liver glycogen, intramuscular lipid, adipose
tissue triglycerides, and amino acids from muscle, blood,
liver and the gut. As oxygen becomes more available to the
working muscle, the body uses more of the aerobic (oxidative)
pathways and less of the anaerobic (phosphagen and
glycolytic) pathways. The greater dependence upon aerobic
pathways does not occur abruptly, nor is one pathway ever
relied on exclusively. The intensity, duration, frequency, type
of training, sex, and training level of the individual, as well as
prior nutrient intake and substrate availability, determine the
relative contribution of energy pathways and when crossover
between pathways occurs. For a more complete understanding
of fuel systems for exercise, the reader is directed to
specific texts.29
An athlete_s skeletal muscle has a remarkable plasticity to
respond quickly to mechanical loading and nutrient availability
resulting in condition-specific metabolic and functional
adaptations.30
These adaptations influence performance nutrition
recommendations with the overarching goals that energy
systems should be trained to provide the most economical
support for the fuel demands of an event while other strategies
should achieve appropriate substrate availability during the
event itself. Adaptations that enhance metabolic flexibility
include increases in transport molecules that carry nutrients
across membranes or to the site of their utilization within the
muscle cell, increases in enzymes that activate or regulate
metabolic pathways, enhancement of the ability to tolerate the
side-products of metabolism and an increase in the size of
muscle fuel stores.3
While some muscle substrates (eg, body
fat) are present in relatively large quantities, others may need
to be manipulated according to specific needs (eg, carbohydrate
supplementation to replace muscle glycogen stores).
Carbohydrate. Carbohydrate has rightfully received a
great deal of attention in sports nutrition due to a number of
special features of its role in the performance of, and adaptation
to training. First, the size of body carbohydrate stores
is relatively limited and can be acutely manipulated on a
daily basis by dietary intake or even a single session of ex-
ercise.3
Second, carbohydrate provides a key fuel for the
brain and central nervous system and a versatile substrate for
muscular work where it can support exercise over a large
range of intensities due to its utilization by both anaerobic
and oxidative pathways. Even when working at the highest
intensities that can be supported by oxidative phosphorylation,
carbohydrate offers advantages over fat as a substrate
since it provides a greater yield of adenosine triphosphate per
volume of oxygen that can be delivered to the mitochondria,3
thus improving gross exercise efficiency.31
Third, there is
significant evidence that the performance of prolonged
sustained or intermittent high-intensity exercise is enhanced
by strategies that maintain high carbohydrate availability
(ie, match glycogen stores and blood glucose to the fuel
demands of exercise), while depletion of these stores is associated
with fatigue in the form of reduced work rates,
impaired skill and concentration, and increased perception
of effort. These findings underpin the various performance
nutrition strategies, to be discussed subsequently, that supply
carbohydrate before, during, and in the recovery between
events to enhance carbohydrate availability.
Finally, recent work has identified that in addition to its
role as a muscle substrate, glycogen plays important direct
and indirect roles in regulating the muscle_s adaptation to
training. 32
The amount and localization of glycogen within
the muscle cell alters the physical, metabolic, and hormonal
environment in which the signaling responses to exercise are
exerted. Specifically, starting a bout of endurance exercise
with low muscle glycogen content (e.g. by undertaking a
second training session in the hours after the prior session
has depleted glycogen stores) produces a coordinated upregulation
of the transcriptional and post-translational responses
to exercise. A number of mechanisms underpin this
outcome including increasing the activity of molecules that
have a glycogen binding domain, increasing free fatty acid
availability, changing osmotic pressure in the muscle cell
and increasing catecholamine concentrations.32
Strategies
that restrict exogenous carbohydrate availability (e.g. exercising
in a fasted state or without carbohydrate intake during the session)
also promote an extended signaling response, albeit less
robustly than is the case for exercise with low endogenous
carbohydrate stores.33
These strategies enhance the cellular
outcomes of endurance training such as increased maximal
mitochondrial enzyme activities and/or mitochondrial content
and increased rates of lipid oxidation, with the augmentation of
responses likely to be explained by enhanced activation of key
cell signaling kinases (eg, AMPK, p38MAPK), transcription
factors (eg, p53, PPARC) and transcriptional co-activators (eg,
PGC-1>).33
Deliberate integration of such training-dietary
strategies (‘‘train low’’) within the periodized training program
is becoming a recognized,34
although potentially
misused,33
part of sports nutrition practice.
Individualized recommendations for daily intakes of carbohydrate
should be made in consideration of the athlete_s
training/competition program and the relative importance of
undertaking it with high or low carbohydrate according to
the priority of promoting the performance of high quality
exercise versus enhancing the training stimulus or adaptation,
respectively. Unfortunately, we lack sophisticated information
on the specific substrate requirements of many of
the training sessions undertaken by athletes; therefore we
must rely on guesswork, supported by information on work
requirements of exercise from technologies such as consumerbased
activity and heart rate monitors,35
power meters, and
global positioning systems.
General guidelines for the suggested intake of carbohydrate
to provide high carbohydrate availability for designated
training or competition sessions can be provided according
to the athlete_s body size (a proxy for the size of muscle
stores) and the characteristics of the session (Table 2). The
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timing of carbohydrate intake over the day and in relation to
training can also be manipulated to promote or reduce carbohydrate
availability.36
Strategies to enhance carbohydrate
availability are covered in more detail in relation to competition
eating strategies. Nevertheless, these fueling practices
are also important for supporting the high quality workouts
within the periodized training program. Furthermore, it is
intuitive that they add value in fine-tuning intended event
eating strategies, and for promoting adaptations such as gastrointestinal
tolerance and enhanced intestinal absorption37
that allow competition strategies to be fully effective. During
other sessions of the training program, it may be less important
to achieve high carbohydrate availability, or there may be
some value in deliberately exercising with low carbohydrate
availability to enhance the training stimulus or adaptive response.
Various tactics can be used to permit or promote low
carbohydrate availability including reducing total carbohydrate
intake or manipulating the timing of training in relation
to carbohydrate intake (eg, training in a fasted state, undertaking
two bouts of exercise in close proximity without opportunity
for refueling between sessions).38
Specific questions examined via the evidence analysis on
carbohydrate needs for training are summarized in Table 2
and show good evidence that neither the glycemic load
nor glycemic index of carbohydrate-rich meals affects
the metabolic nor performance outcomes of training once
TABLE 2. Summary of guidelines for carbohydrate intake by athletes.36
Situation Carbohydrate Targets Comments on Type and Timing of Carbohydrate Intake
DAILY NEEDS FOR FUEL AND RECOVERY
1. The following targets are intended to provide high carbohydrate availability (ie, to meet the carbohydrate needs of the muscle and central nervous system) for different exercise
loads for scenarios where it is important to exercise with high quality and/or at high intensity. These general recommendations should be fine-tuned with individual consideration
of total energy needs, specific training needs and feedback from training performance.
2. On other occasions, when exercise quality or intensity is less important, it may be less important to achieve these carbohydrate targets or to arrange carbohydrate intake over the
day to optimise availability for specific sessions. In these cases, carbohydrate intake may be chosen to suit energy goals, food preferences, or food availability.
3. In some scenarios, when the focus is on enhancing the training stimulus or adaptive response, low carbohydrate availability may be deliberately achieved by reducing total
carbohydrate intake, or by manipulating carbohydrate intake related to training sessions (eg, training in a fasted state, undertaking a second session of exercise without
adequate opportunity for refuelling after the first session).
Light  Low intensity or skill-based
activities
3–5 g/kg of athlete_s body
weight/d
 Timing of intake of carbohydrate over the day may
be manipulated to promote high carbohydrate availability
for a specific session by consuming carbohydrate before
or during the session, or in recovery from a previous session.
Moderate  Moderate exercise program
(eg, ~1 h per day)
5–7 g/kg/d
 Otherwise, as long as total fuel needs are provided, the pattern of
intake may simply be guided by convenience and individual choice.
High  Endurance program (eg, 1–3 h/d
mod-high-intensity exercise)
6–10 g/kg/d
 Athletes should choose nutrient-rich carbohydrate sources to
allow overall nutrient needs to be met.
Very High  Extreme commitment (eg, 94–5 h/d
mod-high intensity exercise
8–12 g/kg/d
ACUTE FUELLING STRATEGIES – these guidelines promote high carbohydrate availability to promote optimal performance in competition or key training sessions
General fuelling up  Preparation for events G 90 min
exercise
7–12 g/kg per 24 h as for
daily fuel needs
 Athletes may choose carbohydrate-rich sources that are low in
fiber/residue and easily consumed to ensure that fuel targets are
met, and to meet goals for gut comfort or lighter ‘‘racing weight’’.Carbohydrate loading  Preparation for events 9 90 min of
sustained/intermittent exercise
36–48 h of 10–12 g/kg body
weight per 24 h
Speedy refuelling  G8 h recovery between 2 fuel
demanding sessions
1–1.2 g/kg/h for first 4 h then
resume daily fuel needs
 There may be benefits in consuming small regular snacks
 Carbohydrate rich foods and drink may help to ensure that
fuel targets are met.
Pre-event fuelling  Before exercise 9 60 min 1–4 g/kg consumed 1–4 h
before exercise
 Timing, amount and type of carbohydrate foods and drinks should
be chosen to suit the practical needs of the event and individual
preferences/experiences.
 Choices high in fat/protein/fiber may need to be avoided to
reduce risk of gastrointestinal issues during the event.
 Low glycemic index choices may provide a more sustained source
of fuel for situations where carbohydrate cannot be consumed
during exercise.
During brief exercise  G45 min Not needed
During sustained high intensity
exercise
 45–75 min Small amounts including
mouth rinse
 A range of drinks and sports products can provide easily
consumed carbohydrate.
 The frequent contact of carbohydrate with the mouth and
oral cavity can stimulate parts of the brain and central nervous
system to enhance perceptions of well-being and increase
self-chosen work outputs.
During endurance exercise
including ‘‘stop and start’’ sports
 1–2.5 h 30–60 g/h  Carbohydrate intake provides a source of fuel for the muscle to
supplement endogenous stores.
 Opportunities to consume foods and drinks vary according to the
rules and nature of each sport.
 A range of everyday dietary choices and specialised sports
products ranging in form from liquid to solid may be useful
 The athlete should practice to find a refuelling plan that suits their
individual goals including hydration needs and gut comfort.
During ultra-endurance exercise  92.5–3 h Up to 90 g/h  As above.
 Higher intakes of carbohydrate are associated with better
performance.
 Products providing multiple transportable carbohydrates
(Glucose:fructose mixtures) achieve high rates of oxidation of
carbohydrate consumed during exercise.
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carbohydrate and energy content of the diet have been taken
into account (Question #11). Furthermore, although there is
sound theory behind the metabolic advantages of exercising
with low carbohydrate availability on training adaptations,
the benefits to performance outcomes are currently unclear
(Table 1, Question #10). This possibly relates to the limitations
of the few available studies in which poor periodization
of this tactic within the training program has meant that any
advantages to training adaptations have been counteracted by
the reduction in training intensity and quality associated with
low carbohydrate variability. Therefore, a more sophisticated
approach is needed to integrate this training/nutrient interaction
into the larger training program.33
Finally, while there is
support for consuming multiple carbohydrates to facilitate
more rapid absorption, evidence to support the choice of
special blends of carbohydrate to support increased carbohydrate
oxidation during training sessions is premature
(Question #9).
Protein. Dietary protein interacts with exercise, providing
both a trigger and a substrate for the synthesis of contractile
and metabolic proteins39,40
as well as enhancing
structural changes in non-muscle tissues such as tendons41
and bones.42
Adaptations are thought to occur by stimulation
of the activity of the protein synthetic machinery in
response to a rise in leucine concentrations and the provision
of an exogenous source of amino acids for incorporation into
new proteins.43
Studies of the response to resistance training
show upregulation of muscle protein synthesis (MPS) for
at least 24 hours in response to a single session of exercise,
with increased sensitivity to the intake of dietary protein
over this period.44
This contributes to improvements in
skeletal muscle protein accretion observed in prospective
studies that incorporate multiple protein feedings after
exercise and throughout the day. Similar responses occur
following aerobic exercise or other exercise types (eg, intermittent
sprint activities and concurrent exercise), albeit
with potential differences in the type of proteins that are
synthesized. Recent recommendations have underscored the
importance of well-timed protein intake for all athletes even
if muscle hypertrophy is not the primary training goal, and
there is now good rationale for recommending daily protein
intakes that are well above the RDA39
to maximize metabolic
adaptation to training.40
Although classical nitrogen balance work has been useful
for determining protein requirements to prevent deficiency
in sedentary humans in energy balance,45
athletes do not
meet this profile and achieving nitrogen balance is secondary
to an athlete with the primary goal of adaptation to
training and performance improvement.40
The modern view
for establishing recommendations for protein intake in athletes
extends beyond the DRIs. Focus has clearly shifted to
evaluating the benefits of providing enough protein at optimal
times to support tissues with rapid turnover and augment
metabolic adaptations initiated by training stimulus.
Future research will further refine recommendations directed
at total daily amounts, timing strategies, quality of protein
intake, and provide new recommendations for protein supplements
derived from various protein sources.
Protein needs. Current data suggest that dietary protein
intake necessary to support metabolic adaptation, repair,
remodeling, and for protein turnover generally ranges from
1.2 to 2.0 g/kg/d. Higher intakes may be indicated for short
periods during intensified training or when reducing energy
intake.26,39
Daily protein intake goals should be met with a
meal plan providing a regular spread of moderate amounts
of high-quality protein across the day and following strenuous
training sessions. These recommendations encompass
most training regimens and allow for flexible adjustments with
periodized training and experience.46,47
Although general
daily ranges are provided, individuals should no longer be
solely categorized as strength or endurance athletes and provided
with static daily protein intake targets. Rather, guidelines
should be based around optimal adaptation to specific
sessions of training/competition within a periodized program,
underpinned by an appreciation of the larger context of athletic
goals, nutrient needs, energy considerations, and food
choices. Requirements can fluctuate based on ‘‘trained’’ status
(experienced athletes requiring less), training (sessions involving
higher frequency and intensity, or a new training
stimulus at higher end of protein range), carbohydrate availability,
and most importantly, energy availability.46,48
The
consumption of adequate energy, particularly from carbohydrates,
to match energy expenditure, is important so that amino
acids are spared for protein synthesis and not oxidized.49
In
cases of energy restriction or sudden inactivity as occurs as a
result of injury, elevated protein intakes as high as 2.0 g/kg/day
or higher26,50
when spread over the day may be advantageous
in preventing fat-free mass loss.39
More detailed reviews of
factors that influence changing protein needs and their relationship
to changes in protein metabolism and body composition
goals can be found elsewhere.51,52
Protein timing as a trigger for metabolic adaptation.
Laboratory based studies show that MPS is optimized
in response to exercise by the consumption of high
biological value protein, providing ~10 g essential amino
acids in the early recovery phase (0–2 h after exercise).40,53
This translates to a recommended protein intake of 0.25–
0.3 g/kg body weight or 15–25 g protein across the typical
range of athlete body sizes, although the guidelines may need
to be fine-tuned for athletes at extreme ends of the weight
spectrum.54
Higher doses (ie, 940 g dietary protein) have not
yet been shown to further augment MPS and may only be
prudent for the largest athletes, or during weight loss.54
The
exercise-enhancement of MPS, determined by the timing and
pattern of protein intake, responds to further intake of protein
within the 24-hour period after exercise,55
and may ultimately
translate into chronic muscle protein accretion and functional
change. While protein timing affects MPS rates, the magnitude
of mass and strength changes over time are less clear.56
However, longitudinal training studies currently suggest that
increases in strength and muscle mass are greatest with immediate
post-exercise provision of protein.57
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Whereas traditional protein intake guidelines focused on
total protein intake over the day (g/kg), newer recommendations
now highlight that the muscle adaptation to training can
be maximized by ingesting these targets as 0.3 g/kg body
weight after key exercise sessions and every 3–5 hours over
multiple meals.47,54,58
Table 1, Question #8 summarizes the
weight of the current literature of consuming protein on
protein-specific metabolic responses during recovery.
Optimal protein sources. High-quality dietary proteins
are effective for the maintenance, repair, and synthesis
of skeletal muscle proteins.59
Chronic training studies have
shown that the consumption of milk-based protein after resistance
exercise is effective in increasing muscle strength
and favorable changes in body composition.57,60,61
In addition,
there are reports of increased MPS and protein accretion
with whole milk, lean meat, and dietary supplements,
some of which provide the isolated proteins whey, casein,
soy, and egg. To date, dairy proteins seem to be superior to
other tested proteins, largely due to leucine content and the
digestion and absorptive kinetics of branched-chain amino
acids in fluid-based dairy foods.62
However, further studies
are warranted to assess other intact high-quality protein
sources (eg, egg, beef, pork, concentrated vegetable protein)
and mixed meals on mTOR stimulation and MPS following
various modes of exercise. When whole food protein sources
are not convenient or available, then portable, third-party
tested dietary supplements with high-quality ingredients
may serve as a practical alternative to help athletes meet
their protein needs. It is important to conduct a thorough
assessment of the athlete_s specific nutrition goals when
considering protein supplements. Recommendations regarding
protein supplements should be conservative and primarily
directed at optimizing recovery and adaptation to training
while continuing to focus on strategies to improve or maintain
overall diet quality.
Fat. Fat is a necessary component of a healthy diet, providing
energy, essential elements of cell membranes and
facilitation of the absorption of fat-soluble vitamins. The
Dietary Guidelines for Americans, 2015–20208
and Eating
Well with Canada_s Food Guide63
have made recommendations
that the proportion of energy from saturated fats be
limited to less than 10% and include sources of essential fatty
acids to meet adequate intake (AI) recommendations. Intake
of fat by athletes should be in accordance with public health
guidelines and should be individualized based on training
level and body composition goals.46
Fat, in the form of plasma free fatty acids, intramuscular
triglycerides and adipose tissue provides a fuel substrate that
is both relatively plentiful and increased in availability to the
muscle as a result of endurance training. However, exerciseinduced
adaptations do not appear to maximize oxidation
rates since they can be further enhanced by dietary strategies
such as fasting, acute pre-exercise intake of fat and chronic
exposure to high-fat, low-carbohydrate diets.3
Although
there has been historical64
and recently revived65
interest in
chronic adaptation to high-fat low carbohydrate diets, the
present evidence suggests that enhanced rates of fat oxidation
can only match exercise capacity/performance achieved by
diets or strategies promoting high carbohydrate availability at
moderate intensities,64
while the performance of exercise at
the higher intensities is impaired.64,66
This appears to occur
as a result of a down-regulation of carbohydrate metabolism
even when glycogen is available.67
Further research is
warranted both in view of the current discussions65
and the
failure of current studies to include an adequate control diet
that includes contemporary periodized dietary approaches.68
Although specific scenarios may exist where high-fat diets
may offer some benefits or at least the absence of disadvantages
for performance, in general they appear to reduce rather
than enhance metabolic flexibility by reducing carbohydrate
availability and capacity to use it effectively as an exercise
substrate. Therefore, competitive athletes would be unwise to
sacrifice their ability to undertake high-quality training or
high-intensity efforts during competition that could determine
the outcome.68
Conversely, athletes may choose to excessively restrict
their fat intake in an effort to lose body weight or improve
body composition. Athletes should be discouraged from
chronic implementation of fat intakes below 20% of energy
intake since the reduction in dietary variety often associated
with such restrictions is likely to reduce the intake of a variety
of nutrients such as fat-soluble vitamins and essential
fatty acids,9
especially n-3 fatty acids. If such focused restrictiveness
around fat intake is practiced, it should be
limited to acute scenarios such as the pre-event diet or
carbohydrate-loading where considerations of preferred
macronutrients or gastrointestinal comfort have priority.
Alcohol. Alcohol consumption may be part of a wellchosen
diet and social interactions, but excessive alcohol
consistent with binge drinking patterns is a concerning behavior
observed among some athletes, particularly in team
sports.69
Misuse of alcohol can interfere with athletic goals in
a variety of ways related to the negative effects of acute intake
of alcohol on the performance of, or recovery from, exercise,
or the chronic effects of binge drinking on health and management
of body composition.70
Besides the calorie load of
alcohol (7 kcal/g), alcohol suppresses lipid oxidation, increases
unplanned food consumption and may compromise
the achievement of body composition goals. Research in this
area is fraught with study design concerns that limit direct
translation to athletes.
Available evidence warns against intake of significant
amounts of alcohol in the pre-exercise period and during
training due to the direct negative effects of alcohol on exercise
metabolism, thermoregulation, and skills/concentration.69
The
effects of alcohol on strength and performance may persist for
several hours even after signs and symptoms of intoxication
or hangover are no longer present. In the post-exercise phase,
where cultural patterns in sport often promote alcohol use,
alcohol may interfere with recovery by impairing glycogen
storage, 71
slowing rates of rehydration via its suppressive
effect on anti-diuretic hormone,72
and impairing the MPS
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desired for adaptation and repair.69,73,74
In cold environments,
alcohol consumption increases peripheral vasodilation resulting
in core temperature dysregulation75
and there are likely
to be other effects on body function such as disturbances in
acid–base balance and cytokine-prostaglandin pathways,
and compromised glucose metabolism and cardiovascular
function.76
Binge drinking may indirectly affect recovery
goals due to inattention to guidelines for recovery. Binge
drinking is also associated with high-risk behaviors leading
to accidents and anti-social behaviors that can be detrimental
to the athlete. In conclusion, athletes are advised to consider
both public health guidelines and team rules regarding use of
alcohol and are encouraged to minimize or avoid alcohol
consumption in the post-exercise period when issues of recovery
and injury repair are a priority.
Micronutrients. Exercise stresses many of the metabolic
pathways in which micronutrients are required, and
training may result in muscle biochemical adaptations that
increase the need for some micronutrients. Athletes who
frequently restrict energy intake, rely on extreme weight-loss
practices, eliminate one or more food groups from their diet, or
consume poorly chosen diets, may consume sub-optimal
amounts of micronutrients and benefit from micronutrient
supplementation.77
This occurs most frequently in the case of
calcium, vitamin D, iron, and some antioxidants.78–80
Singlemicronutrient
supplements are generally only appropriate for
correction of a clinically-defined medical reason [eg, iron
supplements for iron deficiency anemia (IDA)].
Micronutrients of key interest: Iron. Iron deficiency,
with or without anemia, can impair muscle function and limit
work capacity 78,81
leading to compromised training adaptation
and athletic performance. Suboptimal iron status often
results from limited iron intake from heme food sources and
inadequate energy intake (approximately 6 mg iron is consumed
per ~1,000 kcals).82
Periods of rapid growth, training
at high altitudes, menstrual blood loss, foot-strike hemolysis,
blood donation, or injury can negatively impact iron
status.79,81
Some athletes in intense training may also have
increased iron losses in sweat, urine, feces, and from intravascular
hemolysis.
Regardless of the etiology, a compromised iron status can
negatively impact health, physical and mental performance,
and warrants prompt medical intervention and monitoring.83
Iron requirements for all female athletes may be increased by
up to 70% of the estimated average requirement.84
Athletes
who are at greatest risk, such as distance runners, vegetarian
athletes, or regular blood donors should be screened regularly
and aim for an iron intake greater than their RDA
(ie, 918 mg for women and 98 mg for men).81,85
Athletes with iron deficiency anemia (IDA) should seek
clinical follow up, with therapies including oral iron sup-
plementation,86
improvements in diet and a possible reduction
in activities that impact iron loss (eg, blood donation, a
reduction in weight bearing training to lessen erythrocyte he-
molysis).87
The intake of iron supplements in the period immediately
after strenuous exercise is contra-indicated since
there is the potential for elevated hepcidin levels to interfere with
iron absorption.88
Reversing IDA can require 3 to 6 months;
therefore, it is advantageous to begin nutrition intervention
before IDA develops.78,81
Athletes who are concerned about
iron status or have iron deficiency without anemia (eg, low
ferritin without IDA) should adopt eating strategies that promote
an increased intake of food sources of well-absorbed
iron (eg, heme iron, non-heme iron + vitamin C foods) as the
first line of defense. Although there is some evidence that iron
supplements can achieve performance improvements in athletes
with iron depletion who are not anemic,89
athletes
should be educated that routine, unmonitored supplementation
is not recommended, not considered ergogenic without
clinical evidence of iron depletion, and may cause unwanted
gastrointestinal distress.89
Some athletes may experience a transient decrease in
hemoglobin at the initiation of training due to hemodilution,
known as ‘‘dilutional’’ or ‘‘sports anemia’’, and may
not respond to nutrition intervention. These changes appear
to be a beneficial adaptation to aerobic training and do
not negatively impact performance.79
There is no agreement
on the serum ferritin level that corresponds to a
problematic level of iron depletion/deficiency, with various
suggestions ranging from G10 to G35 ng/mL.86
A
thorough clinical evaluation in this scenario is warranted
since ferritin is an acute-phase protein that increases with inflammation,
but in the absence of inflammation, still serves as
the best early indicator of compromised iron status. Other
markers of iron status and other issues in iron metabolism (e.g.
the role of hepcidin) are currently being explored.88
Micronutrients of key interest: Vitamin D. Vitamin
D regulates calcium and phosphorus absorption and metabolism,
and plays a key role in maintaining bone health. There is
also emerging scientific interest in the biomolecular role of
vitamin D in skeletal muscle90
where its role in mediating
muscle metabolic function91
may have implications for
supporting athletic performance. A growing number of studies
have documented the relationship between vitamin D
status and injury prevention,92
rehabilitation,93
improved
neuromuscular function,94
increased type II muscle fiber
size,94
reduced inflammation,93
decreased risk of stress frac-
ture,92,95
and acute respiratory illness.95
Athletes who live at latitudes 935th parallel or who primarily
train and compete indoors are likely at higher risk for
vitamin D insufficiency (25(OH) D = 50-75 nmol/L) and
deficiency (25(OH) D G50 nmol/L). Other factors and lifestyle
habits such as dark complexion, high body fat content,
undertaking of training in the early morning and evening
when UVB levels are low, and aggressive blocking of UVB
exposure (clothing, equipment, and screening/blocking lotions)
increase the risk for insufficiency and deficiency.93
Since athletes tend to consume little vitamin D from the
diet93
and dietary interventions alone have not been shown
to be a reliable means to resolve insufficient status,96
supplementation
above the current RDA and/or responsible UVB
exposure may be required to maintain sufficient vitamin D
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status. A recent study of NCAA Division 1 swimmers and
divers reported that athletes who started at 130 nmol/L and
received daily doses of 4,000 IU of vitamin D (100 Kg)
were able to maintain sufficient status over 6 months (mean
change +2.5 nmol/L), while athletes receiving placebo experienced
a mean loss of 50 nmol/L.97
Unfortunately, determining
vitamin D requirements for optimal health and
performance is a complex process. Vitamin D blood levels
from 80 nmol/L and up to 100 nmol/L93
to 125 nmol/L94
have been recognized as prudent goals for optimal training
induced adaptation. Although proper assessment and correction
of deficiency is likely vital to athlete well-being and
athletic success, current data do not support vitamin D as an
ergogenic aid for athletes. Empirical data are still needed to
elucidate the direct role of vitamin D in musculoskeletal
health and function to help refine recommendations for athletes.
Until then, athletes with a history of stress fracture, bone
or joint injury, signs of over training, muscle pain or weakness,
and a lifestyle involving low exposure to UVB may require
25(OH)D assessment98
to determine if an individualized
vitamin D supplementation protocol is required.
Micronutrients of key interest: Calcium. Calcium
is especially important for growth, maintenance, and repair
of bone tissue; regulation of muscle contraction; nerve
conduction; and normal blood clotting. The risk of low
bone-mineral density and stress fractures is increased by low
energy availability, and in the case of female athletes,
menstrual dysfunction, with low dietary calcium intake
contributing further to the risk.78,99,100
Low calcium intakes
are associated with restricted energy intake, disordered eating
and/or the specific avoidance of dairy products or other
calcium-rich foods. Calcium supplementation should be
determined after a thorough assessment of usual dietary intake.
Calcium intakes of 1,500 mg/d and 1,500–2,000 IU/day
of vitamin D are needed to optimize bone health in athletes
with low energy availability or menstrual dysfunctions.12
Micronutrients of key interest: Antioxidants. Antioxidant
nutrients play important roles in protecting cell
membranes from oxidative damage. Because exercise can
increase oxygen consumption by 10- to 15-fold, it has been
hypothesized that chronic training contributes a constant
‘‘oxidative stress’’ on cells.101
Acute exercise is known to
increase levels of lipid peroxide by-products,101
but also results
in a net increase in native antioxidant system functions
and reduced lipid peroxidation.102
Thus, a well-trained athlete
may have a more developed endogenous antioxidant system
than a less-active individual and may not benefit from antioxidant
supplementation, especially if consuming a diet high
in antioxidant rich foods. There is little evidence that antioxidant
supplements enhance athletic performance101
and the
interpretation of existing data is confounded by issues of
study design (eg, a large variability in subject characteristics,
training protocols, and the doses and combinations of antioxidant
supplements; the scarcity of crossover designs).
There is also some evidence that antioxidant supplementation
may negatively influence training adaptations.103
The safest and most effective strategy regarding micronutrient
antioxidants is to consume a well-chosen diet
containing antioxidant-rich foods. The importance of reactive
oxygen species in stimulating optimal adaptation to
training merits further investigation, but the current literature
does not support antioxidant supplementation as a means to
prevent exercise induced oxidative stress. If athletes decide
to pursue supplementation, they should be advised not to
exceed the Tolerable Upper Intake Levels since higher doses
could be pro-oxidative.101
Athletes at greatest risk for poor
antioxidant intakes are those who restrict energy intake,
follow a chronic low-fat diet, or limit dietary intake of fruits,
vegetables, and whole grains.46
In summary of the micronutrients, athletes should be educated
that the intake of vitamin and mineral supplements does
not improve performance unless reversing a pre-existing
deficiency78,79
and the literature to support micronutrient supplementation
is often marred with equivocal findings and weak
evidence. Despite this, many athletes unnecessarily consume
micronutrient supplements even when dietary intake meets
micronutrient needs. Rather than self-diagnosing the need for
micronutrient supplementation, when relevant, athletes should
seek clinical assessment of their micronutrient status within a
larger assessment of their overall dietary practices. Sports
dietitians can offer several strategies for assessing micronutrient
status based on collection of a nutrient intake history
along with observing signs and symptoms associated
with micronutrient deficiency. This is particularly important
for iron, vitamin D, calcium, and antioxidants. By encouraging
athletes to consume a well-chosen diet focused on
food variety, sports dietitians can help athletes avoid micronutrient
deficiencies and gain the benefits of many other
performance-promoting eating strategies. Public health guidelines
such as the DRIs provide micronutrient intake recommendations
for sports dietitians to help athletes avoid both
deficiency and safety concerns associated with excessive intake.
Micronutrient intake from dietary sources and fortified
foods should be assessed alongside micronutrient intake from
all other dietary supplements.
THEME 2: PERFORMANCE NUTRITION:
STRATEGIES TO OPTIMIZE PERFORMANCE
AND RECOVERY FOR COMPETITION AND
KEY TRAINING SESSIONS
Pre-, During and Post-Event Eating
Strategies implemented in pre-, during, and post-exercise
periods must address a number of goals. First they should
support or promote optimal performance by addressing various
factors related to nutrition that can cause fatigue and deterioration
in the outputs of performance (eg, power, strength, agility,
skill, and concentration) throughout or towards the end of the
sporting event. These factors include, but are not limited to,
dehydration, electrolyte imbalances, glycogen depletion, hypoglycemia,
gastrointestinal discomfort/upset, and disturbances
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to acid–base balance. Fluids or supplements consumed before,
during, or in the recovery between sessions can reduce or delay
the onset of these factors. Strategies include increasing or replacing
key exercise fuels and providing substrates to return the
body to homeostasis or further adapt to the stress incurred
during a previous exercise session. In some cases, pre-event
nutrition may need to redress the effects of other activities undertaken
by the athlete during event preparation such as dehydration
or restrictive eating associated with ’’making weight’’ in
weight category sports. A secondary goal is to achieve gut
comfort throughout the event, avoiding feelings of hunger or
discomfort and gastrointestinal upsets that may directly reduce
the enjoyment and performance of exercise and interfere with
ongoing nutritional support. A final goal is to continue to
provide nutritional support for health and further adaptation to
exercise, particularly in the case of competitive events that
span days and weeks (eg, tournaments and stage races).
Nutrient needs and the practical strategies for meeting
them pre, during, and post exercise depend on a variety of
factors including the event (mode, intensity, duration of
exercise), the environment, carryover effects from previous
exercise, appetite, and individual responses and preferences.
In competitive situations, rules of the event and access to
nutritional support may also govern the opportunities for
food intake. It is beyond the scope of this review to provide
further discussion other than to comment that solutions to
feeding challenges around exercise require experimentation
and habituation by the athlete, and are often an area in which
the food knowledge, creativity, and practical experiences of
the sports dietitian make valuable contributions to the athlete_s
nutrition plan. Such scenarios are also where the use of sports
foods and supplements are often most valuable, since wellformulated
products can often provide a practical form of
nutritional support to meet specialized nutrient needs.
Hydration Guidelines: Fluid and
Electrolyte Balance
Being appropriately hydrated contributes to optimal health
and exercise performance. In addition to the usual daily water
losses from respiration, gastrointestinal, renal, and sweat
sources, athletes need to replace sweat losses. Sweating assists
with the dissipation of heat, generated as a byproduct of
muscular work but is often exacerbated by environmental
conditions, and thus helps maintain body temperature within
acceptable ranges.104
Dehydration refers to the process of
losing body water and leads to hypohydration. Although it is
common to interchange these terms, there are subtle differences
since they reflect process and outcome.
Through a cascade of events, the metabolic heat generated
by muscle contractions during exercise can eventually lead
to hypovolemia (decreased plasma/blood volume) and thus,
cardiovascular strain, increased glycogen utilization, altered
metabolic and CNS function, and a greater rise in body
temperature.104–106
Although it is possible to be hypohydrated
but not hyperthermic (defined as core body temperature
exceeding 40-C; 104-F),107
in some scenarios the extra
thermal strain associated with hypohydration can contribute
to an increased risk of life-threatening exertional heat illness
(heatstroke). In addition to water, sweat contains substantial
but variable amounts of sodium, with lesser amounts of
potassium, calcium, and magnesium.104
To preserve homeostasis,
optimal body function, performance, and perception
of well-being, athletes should strive to undertake
strategies of fluid management before, during, and after
exercise that maintain euhydration. Depending on the athlete,
the type of exercise, and the environment, there are
situations when this goal is more or less important.
Although there is complexity and individuality in the
response to dehydration, fluid deficits of 92% body weight
can compromise cognitive function and aerobic exercise
performances, particularly in hot weather.104,105,108,109
Decrements in the performance of anaerobic or highintensity
activities, sport-specific technical skills, and aerobic
exercise in a cool environment are more commonly
seen when 3%–5% of BW is lost due to dehydration.104,105
Severe hypohydration with water deficits of 6%–10% BW
has more pronounced effects on exercise tolerance, decreases
in cardiac output, sweat production, skin and muscle
blood flow.107
Assuming an athlete is in energy balance, daily hydration
status may be estimated by tracking early morning body
weight (measured upon waking and after voiding) since
acute changes in body weight generally reflect shifts in body
water. Urinary specific gravity and urine osmolality can also
be used to approximate hydration status by measuring the
concentration of the solutes in urine. When assessed from a
midstream collection of the first morning urine sample, a urinary
specific gravity of G 1.020, perhaps ranging to G 1.025 to
account for individual variability,106
is generally indicative
of euhydration. Urinary osmolality reflects hypohydration
when 9900 mOsmol/kg, while euhydration is considered as
G700 mOsmol/kg.104,106
Before exercise. Some athletes begin exercise in a
hypohydrated state, which may adversely affect athletic per-
formances.105,110
Purposeful dehydration to ‘‘make weight’’
may result in a significant fluid deficit, which may be difficult
to restore between ‘‘weigh-in’’ and start of competition.
Similarly, athletes may be hypohydrated at the onset of exercise
due to recent, prolonged training sessions in the heat or
to multiple events in a day.104,105,108,110
Athletes may achieve euhydration prior to exercise by
consuming a fluid volume equivalent to 5–10 ml/kg BW
(~2–4 ml/lb) in the 2 to 4 hours before exercise to achieve
urine that is pale yellow in color while allowing for sufficient
time for excess fluid to be voided.104,108
Sodium consumed
in pre-exercise fluids and foods may help with fluid
retention. Although some athletes attempt to hyper-hydrate
prior to exercise in hot conditions where the rates of sweat
loss or restrictions on fluid intake inevitably lead to a significant
fluid deficit, the use of glycerol and other plasma
expanders for this purpose is now prohibited by the World
Anti-Doping Agency (www.wada-ama.org).
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During exercise. Sweat rates vary during exercise from
0.3–2.4 L/h dependent on exercise intensity, duration, fitness,
heat acclimatization, altitude, and other environmental conditions
(heat, humidity, etc.).104,106,111,112
Ideally, athletes
should drink sufficient fluids during exercise to replace
sweat losses such that the total body fluid deficit is limited to
G2% BW. Various factors may impair the availability of fluid
or opportunities to consume it during exercise and for most
competitive, high caliber athletes, sweat loss generally exceeds
fluid intake. However, individual differences are seen
in drinking behavior and sweat rates in sport, and result in a
range of changes in fluid status from substantial dehydration
to over-hydration.110
Routine measurement of pre- and post-exercise BW, accounting
for urinary losses and drink volume, can help the
athlete estimate sweat losses during sporting activities to
customize their fluid replacement strategies.104
In the absence
of other factors that alter body mass during exercise
(eg, the significant loss of substrate which may occur during
very prolonged events), a loss of 1 kg BW represents approximately
1 L sweat loss. The fluid plan that suits most
athletes and athletic events will typically achieve an intake
of 0.4 to 0.8 L/h,104
although this needs to be customized to
the athlete_s tolerance and experience, their opportunities for
drinking fluids and the benefits of consuming other nutrients
(eg, carbohydrate) in drink form. Ingestion of cold beverages
(0.5 -C) may help reduce core temperature and thus improve
performance in the heat. The presence of flavor in a beverage
may increase palatability and voluntary fluid intake.
Although the typical outcome for competitive athletes is to
develop a fluid deficit over the course of an exercise session,
over the past 2 decades there has been an increasing awareness
that some recreational athletes drink at rates that exceed their
sweat losses and over-hydrate. Over-drinking fluids in excess
of sweat and urinary losses is the primary cause of
hyponatremia (blood sodium G135 mmol/L), also known as
water intoxication, although this can be exacerbated in cases
where there are excessive losses of sodium in sweat and fluid
replacement involving low-sodium beverages.113,114
It can
also be compounded by excessive fluid intake in the hours
or days leading up to the event. Over-hydration is typically
seen in recreational athletes since their work outputs and
sweat rates are lower than competitive athletes, while their
opportunities and belief in the need to drink may be greater.
Women generally have a smaller body size and lower sweat
rates than males and appear to be at greater risk of overdrinking
and possible hyponatremia.104
Symptoms of hyponatremia
during exercise occur particularly when plasma
sodium levels fall below 130 mmol/L and include bloating,
puffiness, weight gain, nausea, vomiting, headache, confusion,
delirium, seizures, respiratory distress, loss of consciousness,
and possibly death if untreated. While the
prevalence of hypohydration and hypernatremia is thought
to be greater than reports of hyperhydration and hyponatremia,
the latter are more dangerous and require prompt
medical attention.104,106,114
Sodium should be ingested during exercise when large
sweat sodium losses occur. Scenarios include athletes with
high sweat rates (91.2 L/h), ‘‘salty sweat,’’ or prolonged
exercise exceeding 2 hours in duration.105,106,109
Although
highly variable, the average concentration of sodium in
sweat approximates 50 mmol/L (~1 g/L) and is hypotonic in
comparison to blood sodium content. Thirst sensation is
often dictated by changes in plasma osmolality and is usually
a good indication of the need to drink but not that the
athlete is dehydrated.108
Older athletes may present with
age-related decreases in thirst sensation and may need encouragement
to drink during and post-exercise.104
Although skeletal muscle cramps are typically caused by muscle
fatigue, they can occur with athletes from all types of sports in
a range of environmental conditions104
and may be associated
with hypohydration and electrolyte imbalances. Athletes who
sweat profusely, especially when overlaid with a high sweat
sodium concentration, may be at greater risk for cramping, particularly
when not acclimatized to the heat and environment.115
After exercise. Most athletes finish exercising with a
fluid deficit and may need to restore euhydration during the
recovery period.104,110
Rehydration strategies should primarily
involve the consumption of water and sodium at a modest
rate that minimizes diuresis/urinary losses.105
The presence of
dietary sodium/sodium chloride (from foods or fluids) helps
to retain ingested fluids, especially extracellular fluids, including
plasma volume. Therefore, athletes should not be
advised to restrict sodium in their post-exercise nutrition
particularly when large sodium losses have been incurred.
Since sweat losses and obligatory urine losses continue during
the post-exercise phase, effective rehydration requires the
intake of a greater volume of fluid (eg, 125%–150%) than the
final fluid deficit (eg, 1.25–1.5 L fluid for every 1 kg BW
lost).104,106
Excessive intake of alcohol in the recovery period
is discouraged due to its diuretic effects. However, the previous
warnings about caffeine as a diuretic appear to be
overstated when it is habitually consumed in moderate (e.g.
G 180 mg) amounts.104
Carbohydrate Intake Guidelines
Because of its role as an important fuel for the muscle and
central nervous system, the availability of carbohydrate stores
is limiting for the performance of prolonged continuous or
intermittent exercise, and is permissive for the performance of
sustained high-intensity sport. The depletion of muscle glycogen
is associated with fatigue and a reduction in the intensity
of sustained exercise, while inadequate carbohydrate for
the central nervous system impairs performance-influencing
factors such as pacing, perceptions of fatigue, motor skill, and
concentration.3,116
As such, a key strategy in promoting optimal
performance in competitive events or key workouts is
matching of body carbohydrate stores with the fuel demands
of the session. Strategies to promote carbohydrate availability
should be undertaken before, during, or in the recovery between
events or high-quality training sessions.
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Achieving adequate muscle glycogen stores. Manipulating
nutrition and exercise in the hours and days prior to
an important exercise bout allows an athlete to commence the
session with glycogen stores that are commensurate with the
estimated fuel costs of the event. In the absence of severe
muscle damage, glycogen stores can be normalised with 24 h
of reduced training and adequate fuel intake 117
(Table 2).
Events 990 minutes in duration may benefit from higher
glycogen stores,118
which can be achieved by a technique
known as carbohydrate loading. This protocol of achieving
supercompensation of muscle glycogen evolved from the
original studies of glycogen storage in the 1960s and, at least
in the case of trained athletes, can be achieved by extending
the period of a carbohydrate-rich diet and tapering training
over 48 h36
(Table 2).
Carbohydrate consumed in meals and/or snacks during
the 1–4 hours pre-exercise may continue to increase body
glycogen stores, particularly liver glycogen levels that have
been depleted by the overnight fast.117
It may also provide a
source of gut glucose release during exercise.117
Carbohydrate
intakes of 1–4 g/kg, with timing, amount, and food choices
suited to the individual, have been shown to enhance endurance
or performance of prolonged exercise (Table 2).117,119
Generally,
foods with a low-fat, low-fiber, and low–moderate
protein content are the preferred choice for this pre-event
menu since they are less prone to cause gastrointestinal problems
and promote gastric emptying.120
Liquid meal supplements
are useful for athletes who suffer from pre-event
nerves or an uncertain pre-event timetable and thus prefer a
more quickly digested option. Above all, the individual athlete
should choose a strategy that suits their situation and
their past experiences and can be fine-tuned with further
experimentation.
The intake of carbohydrate prior to exercise is not always
straightforward since the metabolic effects of the resulting
insulin response include a reduction in fat mobilization and
utilization and concomitant increase in carbohydrate utili-
zation.119
In some individuals, this can cause premature fa-
tigue.121
Strategies to circumvent this problem include
ensuring at least 1 g/kg carbohydrate in the pre-event meal
to compensate for the increased carbohydrate oxidation, including
a protein source at the meal, including some highintensity
efforts in the pre-exercise warm up to stimulate
hepatic gluconeogenesis, and consuming carbohydrate during
the exercise.122
Another approach has been suggested in
the form of choosing pre-exercise meals from carbohydraterich
foods with a low glycemic index, which might reduce the
metabolic changes associated with carbohydrate ingestion as
well as providing a more sustained carbohydrate release during
exercise. Although occasional studies have shown that
such a strategy enhances subsequent exercise capacity,123
as
summarized by the EAL (Table 1 Question #11) and others,119
pre-exercise intake of low glycemic index carbohydrate
choices has not been found to provide a universal benefit to
performance even when the metabolic perturbations of preexercise
carbohydrate intake are attenuated. Furthermore,
consumption of carbohydrate during exercise, as further advised
in Table 2, dampens any effects of pre-exercise carbohydrate
intake on metabolism and performance.124
Depending on characteristics including the type of exercise,
the environment, and the athlete_s preparation and
carbohydrate tolerance, the intake of carbohydrate during
exercise provides a number of benefits to exercise capacity
and performance via mechanisms including glycogen sparing,
provision of an exogenous muscle substrate, prevention
of hypoglycemia, and activation of reward centers in the
central nervous system.116
Robust literature on exercise
carbohydrate feeding has led to the recognition that different
amounts, timing and types of carbohydrate are needed to
achieve these different effects, and that the different effects
may overlap in various events.36,125
Table 2 summarizes the
current guidelines for exercise fueling, noting opportunities
where it may play a metabolic role (events of 960–90 min)
and the newer concept of ‘‘mouth sensing’’ where frequent
exposure of the mouth and oral cavity to carbohydrate is
likely to be effective in enhancing workout and pacing strategies
via a CNS effect.126
Of course, the practical achievement
of these guidelines needs to fit the personal preferences
and experiences of the individual athlete, and the practical
opportunities provided in an event or workout to obtain and
consume carbohydrate-containing fluids or foods. A range of
everyday foods and fluids and formulated sports products that
include sports beverages may be chosen to meet these
guidelines; this includes newer products containing mixtures
of glucose and fructose (the so-called ‘‘multiple transportable
carbohydrates’’), which aim to increase total intestinal
absorption of carbohydrates.127
Although this could be of use
to situations of prolonged exercise where higher rates of exogenous
carbohydrate oxidation might sustain work intensity
in the face of dwindling muscle glycogen stores, the EAL
found that evidence for benefits is currently equivocal (Table 1,
Question #9).
Glycogen restoration is one of the goals of post-exercise recovery,
particularly between bouts of carbohydrate-dependent
exercise where there is a priority on performance in the second
session. Refueling requires adequate carbohydrate intake
(Table 2) and time. Since the rate of glycogen resynthesis is
only ~ 5% per hour, early intake of carbohydrate in the recovery
period (~1–1.2 g/kg/h during the first 4–6 hours) is useful in
maximizing the effective refueling time.117
As long as total
intake of carbohydrate and energy is adequate and overall
nutritional goals are met, meals and snacks can be chosen from
a variety of foods and fluids according to personal preferences
of type and timing of intake.36,117
More research is needed to
investigate how glycogen storage might be enhanced when
energy and carbohydrate intakes are sub-optimal.
Protein intake guidelines. Protein consumption in the
immediate pre- and post-exercise period is often intertwined
with carbohydrate consumption as most athletes consume
foods, beverages, and supplements that contain both macronutrients.
Dietary protein consumed in scenarios of lowcarbohydrate
availability128
and/or restricted energy intake53
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in the early post-exercise recovery period has been found to
enhance and accelerate glycogen repletion. For example, it
has been established that recovery of performance129
and
glycogen repletion rates53
were similar in athletes consuming
0.8 g carbohydrate/kg/BW + 0.4 g protein/kg/BW compared to
athletes consuming only carbohydrate (1.2 g/kg/BW). This may
support exercise performance and benefit athletes frequently
involved in multiple training or competitive sessions over same
or successive days.
Although protein intake may support glycogen resynthesis
and, when consumed in close proximity to strength and endurance
exercise, enhances MPS,59,130
there is a lack of evidence
from well-controlled studies that protein supplementation directly
improves athletic performance.131,132
However, a modest
number of studies have reported that ingesting ~50–100 g of
protein during the recovery period leads to accelerated recovery
of static force and dynamic power production during delayed
onset muscle soreness.133,134
Despite these findings other studies
show no performance effects from acute ingestion of protein at
intake levels that are much more practical to consume on a
regular basis. Furthermore, studies that imply positive findings
when the control group receives a flavored water placebo133
or
a placebo that is not isocaloric are unable to rule out the impact
of post-exercise energy provision on the observed effect.134
Protein ingestion during exercise and during the preexercise
period seems to have less of an impact on MPS than
the post-exercise provision of protein but may still enhance
muscle reconditioning depending on the type of training that
takes place. Co-ingestion of protein and carbohydrate during
2 hours of intermittent resistance-type exercise has been
shown to stimulate MPS during the exercise period135
and
may extend the metabolic adaption window particularly
during ultra–endurance-type exercise bouts.136
Potential
benefits of consuming protein before and during exercise
may be targeted to athletes focused on the MPS response to
resistance exercise and those looking to enhanced recovery
from ultra-endurance exercise.
Table 1, EAL Questions 5–7 summarizes the literature on
consuming protein alone or in combination with carbohydrate
during recovery on several outcomes. More work is needed to
elucidate the relevance and practicality of protein consumption
on subsequent exercise performance and if mechanisms
in this context are exclusive to accelerating muscle glycogen
synthesis. The utility of a protein supplement should also be
measured against the benefits of consuming protein or amino
acids from meals and snacks that are already part of a sports
nutrition plan to meet other performance goals.
Dietary supplements and ergogenic aids. External
and internal motives to enhance performance often
encourage athletes to consider the enticing marketing
and testimonials surrounding supplements and sports foods.
Sports supplements represent an ever growing industry, but a
lack of regulation of manufacture and marketing means that
athletes can fall victim to false advertising and unsubstantiated
claims.137
The prevalence of supplementation among athletes
has been estimated internationally at 37%–89%, with greater
frequencies being reported among elite and older athletes.
Motivations for use include enhancement of performance or
recovery, improvement or maintenance of health, an increase
in energy, compensation for poor nutrition, immune support,
and manipulation of body composition,138,139
yet few athletes
undertake professional assessment of their baseline nutritional
habits. Furthermore, athletes_ supplementation practices are
often guided by family, friends, teammates, coaches, the internet,
and retailers, rather than sports dietitians and other
sport science professionals.138
Considerations regarding the use of sports foods and
supplements include an assessment of efficacy and potency.
In addition, there are safety concerns due to the presence of
overt and hidden ingredients that are toxic and the poor
practices of athletes in consuming inappropriately large
doses or problematic combinations of products. The issue of
compliance to anti-doping codes remains a concern with
potential contamination with banned or non-permissible
substances. This carries significant implications for athletes
who compete under anti-doping codes (eg, National Collegiate
Athletic Association, World Anti-Doping Agency).139
A supplement manufacturer_s claim of ‘‘100% pure,’’ ‘‘pharmaceutical
grade,’’ ‘‘free of banned substances,’’ ‘‘Natural
Health Product – NHPN/NPN’’ (in Canada) or possessing a
drug identification number are not reliable indications that
guarantee a supplement is free of banned substances. However,
commercial, third-party auditing programs can independently
screen dietary supplements for banned and restricted
substances in testing facilities (ISO 17025 accreditation stan-
dard)140
thereby providing a greater assurance of supplement
purity for athletes concerned about avoiding doping violations
and eligibility.
The ethical use of sports supplements is a personal choice
and remains controversial. It is the role of qualified health
professionals, such as a sports dietitian, to build rapport with
athletes and provide credible, evidence-based information
regarding the appropriateness, efficacy and dosage for the
use of sports foods and supplements. After completing a
thorough assessment of an athlete_s nutritional practices
and dietary intake, sports dietitians should assist the athlete
to determine a cost to benefit analysis of their use of a
product, noting that the athlete is responsible for products
ingested and any subsequent consequences (ie, legal, health,
safety issues).139
The benefits of the use of supplements and sports foods
include practical assistance to meet sports nutritional goals,
prevention or treatment of nutrient deficiencies, a placebo
effect, and in some cases, a direct ergogenic effect. However,
this must be carefully balanced against risks, and the
expense and potential for ergolytic effects.139,141
Factors to
consider in the analysis include a theoretical analysis of the
nutritional goal or performance benefit that the product is to
address within the athlete_s specific training or competition
program, the quality of the evidence that the product can
address these goals, previous experience regarding individual
responsiveness, and the health and legal consequences.
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Relatively few supplements that claim ergogenic benefits
are supported by sound evidence.139,141
Research methodologies
on the efficacy of sports supplements are often limited
by small sample sizes, enrollment of untrained subjects,
poor representation of athlete sub-populations (females,
older athletes, athletes with disabilities, etc.), performance
tests that are unreliable or irrelevant, poor control of
confounding variables, and failure to include recommended
sports nutrition practices or the interaction with other sup-
plements.139,141
Even when there is a robust literature on a
sports supplement, it may not cover all applications that are
specific to an event, environment, or individual athlete.
Supplement use is best undertaken as an adjunct to a wellchosen
nutrition plan. It is rarely effective outside these
conditions and not justified in the case of young athletes
who can make significant performance gains via maturation
in age, sports experience, and the development of a sports
nutrition plan.
It is beyond the scope of this paper to address the multitude
of sports supplements used by athletes and caveats
surrounding sport-specific rules allowing their use. The
Australian Institute of Sport has developed a classification
system that ranks sports foods and supplement ingredients
based on significance of scientific evidence and whether a
product is safe, legal, and effective in improving sports
performance.142
Table 3 serves as a general guide to describe
the ergogenic and physiological effects of potentially
beneficial supplements and sport foods.141,143–148
This guide
is not meant to advocate specific supplement use by athletes
and should only be considered in well-defined situations.
THEME 3: SPECIAL POPULATIONS
AND ENVIRONMENTS
Vegetarian Athlete
Athletes may opt for a vegetarian diet for various reasons
from ethnic, religious, and philosophical beliefs to health,
food aversions, and financial constraints or to disguise disordered
eating. As with any self-induced dietary restriction,
it would be prudent to explore whether the vegetarian athlete
also presents with disordered eating or a frank eating disor-
der.13,14
A vegetarian diet can be nutritionally adequate
containing high intakes of fruits, vegetables, whole grains,
nuts, soy products, fiber, phytochemicals, and antioxi-
dants.149
Currently, research is lacking regarding the impact
on athletic performance from long-term vegetarianism
among athletic populations.150
Depending on the extent of dietary limitations, nutrient
concerns for vegetarianism may include energy, protein, fat,
iron, zinc, vitamin B-12,, calcium, n-3 fatty acids,149
and
low intakes of creatine and carnosine.151
Vegetarian athletes
may have an increased risk of lower bone mineral density
and stress fractures.152
Additional practical challenges include
gaining access to suitable foods during travel, restaurant
dining, and at training camps and competition venues.
Vegetarian athletes may benefit from comprehensive dietary
assessments and education to ensure their diets are nutritionally
sound to support training and competition demands.
Altitude
Altitude exposure (ie, daily or intermittent exposure to
92,000 m, 9 6,600 ft) may be a specialized strategy within
an athlete_s training program or simply their daily training
environment.153
One of the goals of specialized altitude
training blocks is to naturally increase red blood cell mass
(erythropoiesis) so that greater amounts of oxygen can be
carried in the blood to enhance subsequent athletic perfor-
mances.112
Initial exposure to altitude leads to a decrease in
plasma volume with corresponding increases in hemoglobin
concentration. Over time there is a net increase in red cell
mass and blood volume therefore greater oxygen carrying
capacity.154
However, possessing sufficient iron stores prior
to altitude training is essential to enable hematological ad-
aptations.154
Consumption of iron-rich foods with or without
iron supplementation may be required by athletes before and
during altitude exposure.
Specific or chronic exposure to a high altitude environment
may increase the risk of illness, infection, and sub-optimal
adaptation to exercise due to direct effects of hypobaric hypoxic
conditions, an unaccustomed volume and intensity of
training, interrupted sleep, and increased UV light exposure.155
The effects are greater with higher elevation and require more
acclimatization to minimize the risk of specific altitude illness.
Adequate nutrition is essential to maximize the desired effect
from altitude training or to support more chronic exposure to a
high altitude environment. Key nutritional concerns include
the adequacy of intake of energy, carbohydrate, protein, fluids,
iron, and antioxidant-rich foods.112
An increased risk of dehydration
at altitude is associated with initial diuresis, increased
ventilation, and low humidity, and exercise sweat
losses. Some experts suggest daily fluid needs as high as 4–5 L
with altitude training and competition, while others encourage
individual monitoring of hydration status to determine fluid
requirements at altitude.112
Extreme Environments
Extreme environmental challenges (heat, cold, humidity,
altitude) require physiological, behavioral, and technological
adaptations to ensure athletes are capable of performing at
their best. Changes in environmental conditions stimulate
thermoregulatory neuronal activity in the brain to increase
heat loss (sweating and skin vasodilation), prevent heat loss
(skin vasoconstriction), or induce heat gain (shivering).
Sympathetic neural activation triggers changes in skin blood
flow to vary convective heat transfer from the core to the
skin (or vice versa) as required for maintaining an optimal
core temperature. Unique considerations of nutritionrelated
concerns are presented when exercising in hot or
cold environments.107,155,156
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Hot environments. When ambient temperature exceeds
body temperature, heat cannot be dissipated by radiation;
furthermore, the potential to dissipate heat by evaporation of
sweat is substantially reduced when the relative humidity is
high.107,156
Heat illness from extreme heat exposure can result
in appetite changes and serious health implications (ie,
heat exhaustion and exertional heat stroke). Heat exhaustion
is characterized by the inability to sustain cardiac output
related to exercise-heat stress causing elevated skin
temperatures with or without hyperthermia (938.5-C).
Symptoms of heat exhaustion can include anxiety, dizziness,
fainting. Exertional heat stroke (body core hyperthermia,
typically 940-C) is the most serious and leads to multi-organ
dysfunction, including brain swelling, with symptoms of central
nervous system abnormalities, delirium, and convulsions, thus
can be life-threatening.107,156
Athletes competing in lengthy events conducted in hot
conditions (eg, tennis match or marathon) and those forced
TABLE 3. Dietary supplements and sports foods with evidence-based uses in sports nutrition.
Category Examples Use Concerns Evidence
Sports food Sports drinks Practical choice to meet sports
nutritional goals especially when
access to food, opportunities to
consume nutrients or gastrointestinal
concerns make it difficult to consume
traditional food and beverages
Cost is greater than whole foods Burke
Sports bars May be used unnecessarily or in
inappropriate protocols
(2015)141
Sports confectionery
Sports gels
Electrolyte supplements
Protein supplements
Liquid meal supplements
Medical supplements Iron supplements Prevention or treatment of nutrient
deficiency under the supervision of
appropriate medical/nutritional expert
May be self-prescribed unnecessarily
without appropriate supervision
or monitoring
Burke (2015)141
Calcium supplements
Vitamin D supplements
Multi-vitamin/mineral
n-3 fatty acids
Specific performance
supplements Ergogenic effects
Physiological effects/mechanism
of ergogenic effect Concerns regarding usea
Evidence
Creatine Improves performance of
repeated bouts of
high-intensity exercise with
short recovery periods
Increases Creatine and Phosphocreatine
concentrations
Associated with acute weight gain
(0.6–1 kg) which may be problematic
in weight sensitive sports
Tarnopolsky
(2010)143
- Direct effect on competition
performance
May also have other effects such as
enhancement of glycogen storage and
direct effect on muscle protein synthesis
May cause gastrointestinal discomfort
- Enhanced capacity for training
Some products may not contain
appropriate amounts or forms
of creatine
Caffeine Reduces perception of fatigue Adenosine antagonist with effects on
many body targets including central
nervous system
Causes side-effects (tremor, anxiety,
increased heart rate, etc.) when
consumed in high doses
Astorino (2010)144
Allows exercise to be sustained
at optimal intensity/output
for longer Promotes Ca2+
release from sarcoplasmic
reticulum
Toxic when consumed in very
large doses
Tarnopolsky
(2010)143
Rules of National Collegiate Athletic
Association competition prohibit
the intake of large doses that
produce urinary caffeine levels
exceeding 15 ug/ml
Burke (2013)145
Some products do not disclose caffeine
dose or may contain other stimulants
Sodium bicarbonate Improves performance of events
that would otherwise be
limited by acid–base disturbances
associated with high rates of
anaerobic glycolysis
When taken as an acute dose pre-exercise,
increases extracellular buffering capacity
May cause gastrointestinal side-effects
which cause performance impairment
rather than benefit
Carr (2011)146
- High intensity events of
1–7 minutes
- Repeated high-intensity sprints
- Capacity for high-intensity ‘‘sprint’’
during endurance exercise
Beta-alanine Improves performance of events
that would otherwise be
limited by acid–base disturbances
associated with high rates of
anaerobic glycolysis
When taken in a chronic protocol,
achieves increase in muscle carnosine
(intracellular buffer)
Some products with rapid absorption
may cause paresthesia (tingling sensation)
Quesnele
(2014)147
- Mostly targeted at high-intensity
exercise lasting 60–240 seconds
- May enhance training capacity
Nitrate Improves exercise tolerance and
economy
Increases plasma nitrite concentrations to
increase production of nitric oxide with
various vascular and metabolic effects
that reduces O2 cost of exercise
Consumption in concentrated food sources
(eg, beetroot juice) may cause gut
discomfort and discoloration of urine
Jones (2014)148
Improves performance in endurance
exercise at least in non-elite athletes Efficacy seems less clear cut in high
caliber athletes
These supplements may perform as claimed but does not imply endorsement by this position stand. a
Athletes should be assisted to undertake a cost to benefit analysis (141) before
using any sports food and supplements with consideration of potential nutritional, physiological, and psychological benefits for their specific event weighed against potential disadvantages.
Specific protocols of use should be tailored to the individual scenario (see references for further information) and specific products should be chosen with consideration of the
risk of contamination with unsafe or illegal chemicals.
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to wear excessive clothing (eg, American football players or
BMX competitors) are at greatest risk of heat illness.111
Strategies to reduce high skin temperatures and large sweat
(fluid and electrolyte) losses are required to minimize cardiovascular
and hyperthermic challenges that may impair
athletic performance when exercising in the heat; athletes
should be regularly monitored when at risk for heat-related
illness.107,156
Specific strategies should include: acclimatization,
individualized hydration plans, regular monitoring of
hydration status, beginning exercise euhydrated, consuming
cold fluids during exercise, and possibly the inclusion of
electrolyte sources.107,156
Cold environments. Athletic performance in cold environments
may present several dietary challenges that require
careful planning for optimal nutritional support. A
large number of sports train and compete in the cold ranging
from endurance athletes (eg, Nordic skiers) through to judged
events (eg, free style ski). Furthermore, drastic, unexpected
environmental changes can turn a warm-weather event (eg,
cross country mountain bike race or triathlon) into extreme
cold conditions in a short period of time leaving unprepared
athletes confronted with performing in the cold.
Primary concerns of exercising in a cold environment
are maintenance of euhydration and body temperature.156
However, exercise-induced heat production and appropriate
clothing are generally sufficient to minimize heat loss.155,156
When adequately prepared (eg, removing wet clothing,
keeping muscles warm after exercise warm-up) athletes
can tolerate severe cold in pursuit of athletic success.
Smaller, leaner athletes are at greater risk of hypothermia
due to increased heat production required to maintain core
temperature and decreased insulation from lower body fat.
Metabolically, energy requirements (from carbohydrates)
are increased, especially when shivering, to maintain core
temperature.155,156
Several factors can increase the risk of hypohydration
when exercising in the cold, such as: cold-induced diuresis,
impaired thirst sensation, reduced desire to drink, limited
access to fluids, self-restricted fluid intake to minimize urination,
sweat losses from over-dressing and increased respiration
with high altitude exposure.
In the cold, hypohydration of 2%–3% BW loss is less
detrimental to endurance performances than similar losses
occurring in the heat.104,155,156
Severe cold exposure may be
problematic on training versus competition days since
training duration may exceed competition duration and officials
may delay competitions in inclement weather yet
athletes may continue to train in similar conditions. Athletes_
energy, macronutrient, and fluid intakes should be regularly
assessed and changes in body weight and hydration status
when exercising in both hot and cold environments. Educating
athletes about modifying their energy, carbohydrate
intakes, and recovery strategies according to training and
competition demands promotes optimal training adaptation
and maintenance of health. Practical advice for preparation
and selection of appropriate foods and fluids that withstand
cold exposure will ensure athletes are equipped to cope with
weather extremes.
THEME 4: ROLES AND RESPONSIBILITIES OF
THE SPORTS DIETITIAN
Sport nutrition practice requires combined knowledge in
several topics: clinical nutrition, nutrition science, exercise
physiology, and application of evidence-based research. Increasingly,
athletes and active individuals seek professionals
to guide them in making optimal food and fluid choices to
support and enhance their physical performances. An experienced
sports dietitian demonstrates the knowledge, skills,
and expertise necessary to help athletes and teams work towards
their performance-related goals.
The Commission on Dietetic Registration (the credentialing
agency for the Academy of Nutrition and Dietetics) has created
a unique credential for registered dietitian nutritionists
who specialize in sports dietetic practice with extensive experience
working with athletes. The Board Certified Specialist
in Sports Dietetics (CSSD) credential is designed as the premier
professional sports nutrition credential in the United
States and is available internationally, including Canada.
Specialists in sports dietetics provide safe, effective, evidencebased
nutrition assessments, guidance, and counseling for
health and performance for athletes, sport organizations, and
physically active individuals and groups. For CSSD certification
details refer to the Commission on Dietetic registration:
www.cdrnet.org. Enhancement of sport nutrition knowledge
and continuing education can also be achieved by completing
recognized post-graduate qualifications such as the 2-year
distance learning diploma in sports nutrition offered by the
International Olympic Committee. For more information refer
to Sports Oracle: www.sportsoracle.com/Nutrition/Home/.
The Academy of Nutrition and Dietetics157
describes the
competencies of the sports dietitian to ‘‘provide medical
nutrition therapy in direct care and design, implement, and
manage safe and effective nutrition strategies that enhance
lifelong health, fitness, and optimal physical performance.’’
Roles and responsibilities of sports dietitians working with
athletes are outlined in Table 4.
SUMMARY
The following summarizes the evidence presented in this
position paper:
Í Athletes need to consume energy that is adequate in amount
and timing of intake during periods of high-intensity and/or
long duration training to maintain health and maximize
training outcomes. Low energy availability can result in
unwanted loss of muscle mass; menstrual dysfunction and
hormonal disturbances; sub-optimal bone density; an increased
risk of fatigue, injury, and illness; impaired adaptation
and a prolonged recovery process.
Í The primary goal of the training diet is to provide nutritional
support to allow the athlete to stay healthy and
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injury-free while maximizing the functional and metabolic
adaptations to a periodized exercise program that prepares
him or her to better achieve the performance demands of
their event. While some nutrition strategies allow the athlete
to train hard and recover quickly, others may target an
enhanced training stimulus or adaptation.
Í The optimal physique, including body size, shape and composition
(eg, muscle mass and body fat levels), depends upon
the sex, age, and heredity of the athlete, and may be sport- and
event-specific. Physique assessment techniques have inherent
limitations of reliability and validity, but with standardized
measurement protocols and careful interpretation of results,
they may provide useful information. Where significant manipulation
of body composition is required, it should ideally
take place well before the competitive season to minimize
the impact on event performance or reliance on rapid weight
loss techniques.
Í Body carbohydrate stores provide an important fuel source
for the brain and muscle during exercise, and are manipulated
by exercise and dietary intake. Recommendations for carbohydrate
intake typically range from 3–10 g/kg BW/d (and
up to 12 g/kg BW/d for extreme and prolonged activities),
depending on the fuel demands of training or competition,
the balance between performance and training adaptation
goals, the athlete_s total energy requirements and body
composition goals. Targets should be individualized to the
athlete and his or her event, and also periodized over the
week, and training cycles of the seasonal calendar according
to changes in exercise volume and the importance of high
carbohydrate availability for different exercise sessions.
Í Recommendations for protein intake typically range from
1.2–2.0 g/kg BW/d, but have more recently been expressed
in terms of the regular spacing of intakes of
modest amounts of high quality protein (0.3 g/kg body
weight) after exercise and throughout the day. Such intakes
can generally be met from food sources. Adequate
energy is needed to optimize protein metabolism, and
when energy availability is reduced (eg, to reduce body
weight/fat), higher protein intakes are needed to support
MPS and retention of fat-free mass.
Í For most athletes, fat intakes associated with eating styles
that accommodate dietary goals typically range from 20%–
35% of total energy intake. Consuming e20% of energy
intake from fat does not benefit performance and extreme
restriction of fat intake may limit the food range needed to
meet overall health and performance goals. Claims that
extremely high-fat, carbohydrate-restricted diets provide a
benefit to the performance of competitive athletes are not
supported by current literature.
Í Athletes should consume diets that provide at least the
Recommended Dietary Allowance (RDA)/Adequate Intake
(AI) for all micronutrients. Athletes who restrict energy
intake or use severe weight-loss practices, eliminate complete
food groups from their diet, or follow other extreme
dietary philosophies are at greatest risk of micronutrient
deficiencies.
Í A primary goal of competition nutrition is to address
nutrition-related factors that may limit performance by
causing fatigue and a deterioration in skill or concentration
over the course of the event. For example, in events that are
dependent on muscle carbohydrate availability, meals eaten in
the day(s) leading up to an event should provide sufficient
carbohydrate to achieve glycogen stores that are commensurate
with the fuel needs of the event. Exercise taper and a
carbohydrate-rich diet (7–12 g/kg BW/d) can normalize muscle
glycogen levels within ~ 24 hours, while extending this to
48 hours can achieve glycogen super-compensation.
Í Foods and fluids consumed in the 1–4 hours prior to an
event should contribute to body carbohydrate stores
(particularly, in the case of early morning events to restore
liver glycogen after the overnight fast), ensure appropriate
hydration status and maintain gastrointestinal
comfort throughout the event. The type, timing and amount
of foods and fluids included in this pre-event meal and/or
snack should be well trialed and individualized according to
the preferences, tolerance, and experiences of each athlete.
Í Dehydration/hypohydration can increase the perception of
effort and impair exercise performance; thus, appropriate
fluid intake before, during, and after exercise is important
for health and optimal performance. The goal of drinking
during exercise is to address sweat losses which occur to
assist thermoregulation. Individualized fluid plans should
be developed to use the opportunities to drink during a
workout or competitive event to replace as much of the
sweat loss as is practical; neither drinking in excess of
sweat rate nor allowing dehydration to reach problematic
levels. After exercise, the athlete should restore fluid balance
by drinking a volume of fluid that is equivalent to
~125–150% of the remaining fluid deficit (eg, 1.25–1.5 L
fluid for every 1 kg BW lost).
Í An additional nutritional strategy for events of greater than
60 minutes duration is to consume carbohydrate according
to its potential to enhance performance. These benefits are
achieved via a variety of mechanisms which may occur
independently or simultaneously and are generally divided
into metabolic (providing fuel to the muscle) and central
(supporting the central nervous system). Typically, an intake
of 30–60 g/hour provides benefits by contributing to muscle
fuel needs and maintaining blood glucose concentrations,
although in very prolonged events (2.5+ h) or other scenarios
where endogenous carbohydrate stores are substantially
depleted, higher intakes (up to 90 g/h) are associated
with better performance. Even in sustained high-intensity
events of 45–75 min where there is little need for carbohydrate
intake to play a metabolic role, frequent exposure
of the mouth and oral cavity to small amounts of carbohydrate
can still enhance performance via stimulation of
the brain and central nervous system.
Í Rapid restoration of performance between physiologically
demanding training sessions or competitive events requires
appropriate intake of fluids, electrolytes, energy, and carbohydrates
to promote rehydration and restore muscle
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glycogen. A carbohydrate intake of ~1.0–1.2 g/kg/h, commencing
during the early recovery phase and continuing for
4 to 6 hours, will optimize rates of resynthesis of muscle
glycogen. The available evidence suggests that the early
intake of high quality protein sources (0.25–0.3 g/kg BW)
will provide amino acids to build and repair muscle tissue
and may enhance glycogen storage in situations where carbohydrate
intake is sub-optimal.
Í In general, vitamin and mineral supplements are unnecessary
for the athlete who consumes a diet providing highenergy
availability from a variety of nutrient-dense foods. A
multivitamin/mineral supplement may be appropriate in some
cases when these conditions do not exist; for example, if an
athlete is following an energy-restricted diet or is unwilling
or unable to consume sufficient dietary variety. Supplementation
recommendations should be individualized, realizing
that targeted supplementation may be indicated to
treat or prevent deficiency (eg, iron, vitamin D, etc.).
Í Athletes should be counseled regarding the appropriate use
of sports foods and nutritional ergogenic aids. Such products
should only be used after careful evaluation for safety, efficacy,
potency and compliance with relevant anti-doping
codes and legal requirements.
Í Vegetarian athletes may be at risk for low intakes of energy,
protein, fat, creatine, carnosine, n-3 fatty acids, and
key micronutrients such as iron, calcium, riboflavin, zinc,
and vitamin B-12.
This Academy of Nutrition and Dietetics, Dietitians of
Canada (DC), and American College of Sports Medicine
(ACSM) position statement was adopted by the Academy
House of Delegates Leadership Team on July 12, 2000 and
reaffirmed on May 25, 2004 and February 15, 2011; approved
by DC on November 17, 2015 and approved by the
ACSM Board of Trustees on November 20, 2015. This position
statement is in effect until December 31, 2019. Position
papers should not be used to indicate endorsement of
products or services.
Authors
Academy: D. Travis Thomas, PhD, RDN, CSSD (College of Health Sciences,
University of Kentucky, Lexington, KY);
DC: Kelly Anne Erdman, MSc, RD, CSSD (Canadian Sport Institute
Calgary/University of Calgary Sport Medicine Centre, Calgary, AB,
Canada);
ACSM: Louise M. Burke, OAM, PhD, APD, FACSM (AIS Sports
Nutrition/Australian Institute of Sport Australia and Mary MacKillop
Institute of Health Research, Australian Catholic University).
Reviewers
Academy
Sports, Cardiovascular and Wellness Nutrition dietetic practice group
(Jackie Buell, PhD, RD, CSSD, ATC Ohio State University, Columbus, OH);
Amanda Carlson-Phillips, MS, RD, CSSD (EXOS - Phoenix, AZ);
Sharon Denny, MS, RD (Academy Knowledge Center, Chicago, IL);
D. Enette Larson-Meyer, PhD, RD, FACSM (University of Wyoming,
Laramie, WY);
TABLE 4. Sports dietitian roles and responsibilities.
Role of Sports Dietitian Responsibilities
Assessment of nutritional needs and current dietary practices  Energy intake, nutrients and fluids before, during and after training and competitions
 Nutrition-related health concerns (eating disorders, food allergies or intolerances, gastrointestinal
disturbances, injury management, muscle cramps, hypoglycemia, etc.) and body composition goals
 Food and fluid intake as well as estimated energy expenditure during rest, taper and travel days
 Nutritional needs during extreme conditions (eg, high altitude training, environmental concerns)
 Adequacy of athlete_s body weight and metabolic risk factors associated with low body weight
 Supplementation practices
 Basic measures of height, body weight, etc. with possible assessment of body composition
Interpretation of test results (eg, biochemistry, anthropometry)  Blood, urine analysis, body composition and physiological testing results, including hydration status
Dietary prescription and education  Dietary strategies to support behavior change for improvements with health, physical performance,
body composition goals and/or eating disorders
 Dietary recommendations prescribed relative to athlete_s personal goals and chief concerns related to
training, body composition, and/or competition nutrition, tapering, and/or periodized fat/weight loss
 Quantity, quality, and timing for food and fluid intake before, during and after training and/or
competition to enhance exercise training capacity, endurance and performance
 Medical nutritional therapeutic advice pertaining to unique dietary considerations (eating disorders,
food allergies, diabetes, gastrointestinal issues, etc.)
 Menu planning, time management, grocery shopping, food preparation, food storage, food budgeting,
food security, and recipe modification for training and/or competition days
 Food selection related to travel, restaurants, and training and competition venue choices
 Supplementation, ergogenic aids, fortified foods, etc. regarding legality, safety, and efficacy
 Sport nutrition education, resource development and support may be with individual athletes,
entire teams, and/or with coaches, athletic trainers, physiologists, food service staff, etc.
Collaboration and integration  Contribution as a member of a multidisciplinary team within sport settings to integrate nutrition
programming into a team or athlete_s annual training and competition plan
 Collaboration with the health care team/performance professionals (physicians, athletic trainer,
physiologists, psychologists, etc.) for the performance management of athletes
Evaluation and professionalism  Evaluation of scientific literature and provision of evidence-based assessment and application to
athletic performance
 Development of oversight of nutrition policies and procedures
 Documentation of measurable outcomes of nutrition services
 Recruitment and retention of clients and athletes in practice
 Provision of reimbursable services (eg, diabetes medical nutrition therapy)
 Promotion of career longevity for active individuals, collegiate and professional athletes
 Service as a mentor for developing sports dietetics professionals
 Maintenance of credential(s) by actively engaging in profession-specific continuing education activities
NUTRITION AND ATHLETIC PERFORMANCE Medicine & Science in Sports & Exercised 563
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Mary Pat Raimondi, MS, RD (Academy Policy Initiatives & Advocacy,
Washington DC);
DC
Ashley Armstrong, MS, RD (Canadian Sport Institute Pacific, Vancouver,
Victoria and Whistler, BC, Canada);
Susan Boegman, BSc, RD, IOC Dip Sport Nutrition (Canadian Sport
Institute Pacific, Victoria BC, Canada);
Susie Langley MS, RD, DS, FDC (Retired, Toronto, ON, Canada);
Marielle Ledoux, PhD, PDt (Professor, University of Montreal, Montreal,
QC, Canada);
Emma McCrudden, MSc (Canadian Sport Institute Pacific, Vancouver,
Victoria and Whistler, BC, Canada);
Pearle Nerenberg, MSc, PDt (Pearle Sports Nutrition, Montreal, QC, Canada);
Erik Sesbreno, BSc, RD, IOC Dip Sport Nutrition (Canadian Sport Institute
Ontario, Toronto, Ontario, Canada).
ACSM
Dan Benardot, PhD, RD, LD, FACSM (Georgia State University
Atlanta, GA);
Kristine Clark, PhD, RDN, FACSM (The Pennsylvania State University,
University Park, PA); Melinda M. Manore, PhD, RD, CSSD, FACSM (Oregon
State University, Corvallis, OR);
Emma Stevenson BSc, PhD (Newcastle University, Newcastle upon
Tyne, Tyne and Wear, UK).
Academy Positions Committee Workgroup
Connie Diekman, Med, RD, CSSD, LD (chair) (Washington University,
St. Louis, MO);
Christine A. Rosenbloom, PhD, RDN, CSSD, FAND (Georgia State
University, Atlanta, GA); Roberta Anding, MS, RD/LD, CDE, CSSD,
FAND (content advisor) (Texas Children_s Hospital, Houston and Houston
Astros MLB Franchise, Houston,TX).
We thank the reviewers for their many constructive comments and suggestions.
The reviewers were not asked to endorse this position or the
supporting paper.
ACSM disclaimer: Care has been taken to confirm the accuracy of
the information present and to describe generally accepted practices.
However, the authors, editors, and publisher are not responsible for errors
or omissions or for any consequences from application of the information
in this publication and make no warranty, expressed or implied, with
respect to the currency, completeness, or accuracy of the contents of the
publication. Application of this information in a particular situation remains
the professional responsibility of the practitioner; the clinical treatments
described and recommended may not be considered absolute and
universal recommendations.
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