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Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and Athletic Performance

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It is the position of the Academy of Nutrition and Dietetics (Academy), Dietitians of Canada (DC), and the American College of Sports Medicine (ACSM) 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, DC, and 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 is a registered dietitian nutritionist and a credentialed sports nutrition expert.
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FROM THE ACADEMY
Position Paper
Position of the Academy of Nutrition and
Dietetics, Dietitians of Canada, and the
American College of Sports Medicine: Nutrition
and Athletic Performance
ABSTRACT
It is the position of the Academy of Nutrition and Dietetics (Academy), Dietitians of
Canada (DC), and the American College of Sports Medicine (ACSM) that the performance
of, and recovery from, sporting activities are enhanced by well-chosen nutrition stra-
tegies. These organizations provide guidelines for the appropriate type, amount, and
timing of intake of food, uids, and supplements to promote optimal health and per-
formance across different scenarios of training and competitive sport. This position
paper was prepared for members of the Academy, DC, and ACSM, other professional
associations, government agencies, industry, and the public. It outlines the Academys,
DCs, and ACSMs stance on nutrition factors that have been determined to inuence
athletic performance and emerging trends in the eld 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 Certied Specialist in Sports Dietetics is a
registered dietitian nutritionist and a credentialed sports nutrition expert.
J Acad Nutr Diet. 2016;116:501-528.
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 nutri-
tion strategies. These organizations provide
guidelines for the appropriate type, amount,
and timing of intake of food, uids, and di-
etary supplements to promote optimal health
and sport performance across different sce-
narios of training and competitive sport.
THIS ARTICLE OUTLINES THE
current energy, nutrient, and
uid recommendations for
active adults and competitive
athletes. These general recommenda-
tions 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), prac-
tical challenges, and food preferences.
EVIDENCE-BASED ANALYSIS
This article was developed using the
Academy of Nutrition and Dietetics
(Academy) Evidence Analysis Library
(EAL) and will outline som e key themes
related to nutrition and athletic per-
formance. The EAL is a synthesis of
relevant nutrition research on impor-
tant dietetics-related practice ques-
tions. The publication range for the
evidence-based analysis spanned
March 2006 to November 2014. For the
details on the systematic review and
methodology go to www.andevidence
library.com.Figure 1 presents the evi-
dence 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
This Academy position paper includes the
authorsindependent review of the litera-
ture in addition to systematic review con-
ducted using the AcademysEvidence
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 benets to
earlier review methods. The major advan-
tage of the approach is the more rigorous
standardization of review criteria, which
minimizes the likelihood of reviewer bias
and increases the ease withwhich disparate
articles may be compared. For a detailed
description of the methods used in the ev-
idence analysis process, access the Aca-
demys Evidence Analysis Process (http:
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
I¼Good; Grade II¼Fair; Grade III¼Limited;
Grade IV Expert Opinion Only; and Grade
V¼Not Assignable (because there is no ev-
idence to support or refute the conclusion).
See grade denitions at www.
andevidencelibrary.com/.
Evidence-based information for this and
other topics can be found at https://www.
andevidencelibrary.com and subscriptions
for nonmembers are purchasableat https://
www.andevidencelibrary.com/store.cfm.
This article is being published concur-
rently on the Dietitians of Canada
website (www.dietitians.ca/sports) and
in Medicine & Science in Sports and
Exercise
.The articles are identical
except for minor stylistic and spelling
differences in keeping with each jour-
nals style. Either citation can be used
when citing this article.
2212-2672/Copyright ª2016 by the
Academy of Nutrition and Dietetics,
American College of Sports Medicine, and
Dietitians of Canada.
http://dx.doi.org/10.1016/j.jand.2015.12.006
*Because credentialing practices vary
internationally, the term sports dieti-
tianwill be used throughout this article
to encompass all terms of accreditation,
including registered dietitian nutritionist
(RDN), registered dietitian (RD), profes-
sional dietitian (PDt), or Board Certied
Specialist in Sports Dietetics (CSSD).
ª2016 by the Academy of Nutrition and Dietetics, American College of
Sports Medicine, and Dietitians of Canada. JOURNAL OF THE ACADEMY OF NUTRITION AND DIETETICS 501
Evidence Analysis Library 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 ve 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
benecial 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 4-12 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-specic 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-specic metabolic responses during recovery.
Grade III - Limited
#4: What is the effect of consuming
carbohydrate 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-
specic metabolic responses during recovery?
Compared to ingestion of carbohydrate alone, coingestion of car-
bohydrate 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 postexercise.
The effect of coingestion of protein with carbohydrate on creatine
kinase levels is inconclusive and shows no impact on muscle sore-
ness postexercise.
Grade I - Good
#6: In adult athletes, what is the effect of
consuming carbohydrate and protein
together on carbohydrate and protein-specic
metabolic responses during recovery?
Coingestion of carbohydrate plus protein, together during the recovery
period, resulted in no clear inuence 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 (postexercise) 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
(continued on next page)
Figure 1. Evidence analysis questions included in the position statement. Evidence grades: Grade I: Good, Grade II: Fair, Grade III:
Limited, Grade IV: Expert opinion only; and Grade V: Not assignable. Refer to http://www.andevidencelibrary.com/ for a complete list
of evidence analysis citations.
FROM THE ACADEMY
502 JOURNAL OF THE ACADEMY OF NUTRITION AND DIETETICS March 2016 Volume 116 Number 3
of original research and review,
consensus statements from sporting
organizations, and opportunities for
qualication 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 ourish in both
the scope of support it offers to ath-
letes and the strength of evidence
that underpins its guidelines. Before
embarking on a discussion of individ-
ual topics, it is valuable to identify a
range of themes in contemporary
sports nutrition that corroborate and
unify the recommendations in this
article.
1. Nutrition goals and require-
ments are not static. Athletes
undertake a periodized pro-
gram in which preparation for
peak performance in targeted
events is achieved by inte-
grating different types of
workouts in the various cycles
of the training calendar. Nutri-
tion support also needs to be
periodized, taking into account
the needs of daily training ses-
sions (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
specicity and uniqueness of
the event, performance goals,
practical challenges, food pref-
erences, and responses to
various strategies.
3. A key goal of training is to
adapt the body to develop
metabolic efciency and exi-
bility, whereas competition
nutrition strategies focus on
providing adequate substrate
stores to meet the fuel de-
mands of the event and sup-
port cognitive function.
4. Energy availability, which con-
siders 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 perio-
dized. Care should be taken to
preserve health and long-term
performance by avoiding prac-
tices that create unacceptably
low energy availability and
psychological stress.
6. Training and nutrition have a
strong interaction in accli-
mating the body to develop
Evidence Analysis Library question Conclusion and evidence grade
Energy balance and body composition
#8: In adult athletes, what is the effect of
consuming protein on carbohydrate- and
protein-specic metabolic responses during
recovery?
Ingesting protein (approximately 20 to 30 g total protein, or approximately
10 g essential amino acids) during exercise or the recovery period
(postexercise) 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 glucoseþfructose)
compared with water placebo, but no differences between the two
carbohydrate blends tested were observed in male cyclists. Exogenous
carbohydrate oxidation was greater in the glucoseþfructose 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, whereas there is
insufcient 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
Figure 1. (continued) Evidence analysis questions included in the position statement. Evidence grades: Grade I: Good, Grade II: Fair,
Grade III: Limited, Grade IV: Expert opinion only; and Grade V: Not assignable. Refer to http://www.andevidencelibrary.com/ for a
complete list of evidence analysis citations.
FROM THE ACADEMY
March 2016 Volume 116 Number 3 JOURNAL OF THE ACADEMY OF NUTRITION AND DIETETICS 503
functional and metabolic ad-
aptations. Although optimal
performance is underpinned
by the provision of proactive
nutrition support, training ad-
aptations may be enhanced in
the absence of such support.
7. Some nutrients (eg, energy,
carbohydrate, and protein)
should be expressed using
guidelines per kilogram body
mass to allow recommenda-
tions to be scaled to the large
range in the body sizes of ath-
letes. Sports nutrition guide-
lines 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 exces-
sive training volume.
9. Competition nutrition should
target specic strategies that
reduce or delay factors that
would otherwise cause fatigue
in an event; these are specic
to the event, the environ-
ment/scenario in which it is
undertaken, and the individ-
ual 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 nutri-
tional components, in the oral
cavity can enhance perceptions
of well-being and increase self-
chosen work rates. Such nd-
ings present opportunities for
intake during shorter events, in
which uid 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 supple-
ments and sports foods is
needed in the face of the high
prevalence of interest in, and
use by, athletes and the evi-
dence that some products can
usefully contribute to a sports
nutrition plan and/or directly
enhance performance. Athletes
should be assisted to undertake
a cost-to-benetanalysisofthe
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 athletes diet because
it supports optimal body function, de-
termines the capacity for intake of
macronutrient and micronutrients, and
assists in manipulating body composi-
tion. An athletes energy intake from
food, uids, and supplements can be
derived from weighed/measured food
records (typically 3 to 7 days), 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 under-
reportingof intakes. Extensiveeducation
regarding the purpose and protocols of
documenting intakes may assist with
compliance and enhance the accuracy
and validity of self-reported information.
Meanwhile, an athletesenergyre-
quirements 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, spe-
cic drugs or medications (eg, caffeine
and nicotine), increases in fat-free mass
(FFM), and possibly the luteal phase of
the menstrual cycle.
2
Aside from re-
ductions in training, energy re-
quirements are lowered by aging,
decreases in 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 con-
sists of the summation of basal meta-
bolic rate (BMR), the thermic effect of
food (TEF), and the thermic effect of
activity (TEA).
TEE[BMRDTEFDTEA
TEA[Planned Exercise Expendi-
tureDSpontaneous Physical Activity
DNonexercise Activity Thermogenesis
Techniques used to measure or esti-
mate components of TEE in sedentary
and moderately active populations can
also be applied to athletes, but there are
some limitations to this approach,
particularly in highly competitive ath-
letes. Because the measurement of BMR
requires subjects to remain exclusivelyat
rest, it is more practical to measure
resting metabolic rate (RMR), which may
be 10% higher. Although population-
specic regression equations are
encouraged, a reasonable estimate of
BMR can be obtained using either the
Cunningham
4
or the Harris-Benedict
5
equations, with an appropriate activity
factor being applied to estimate TEE.
Whereas RMR represents 60% to 80% of
TEE for sedentary individuals, it may be
as little as 38% to 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 ac-
tivity (eg, dgeting), and nonexercise
activity thermogenesis. Energy expen-
diture from exercise can be estimated
in several ways from activity logs
(1 to 7 daysduration) with subjective
estimates of exercise intensity using
activity codes and metabolic equiva-
lents,
6,7
US Dietary Guidelines, 2015,
8
and the Dietary Reference Intakes
(DRIs).
9
The latter two typically un-
derestimate the requirements of ath-
letes because they fail to cover the
range in body size or activity levels of
competitive populations. Energy avail-
ability (EA) is a concept of recent cur-
rency in sports nutrition, which
equates energy intake with re-
quirements for optimal health and
function rather than energy balance.
EA, dened as dietary intake minus
exercise energy expenditure normal-
ized to FFM, is the amount of energy
available to the body to perform all
other functions after the cost of exer-
cise is subtracted.
10
The concept was
rst studied in women, where an EA of
45 kcal/kg FFM/day was found to be
associated with energy balance and
optimal health; meanwhile, a chronic
reduction in EA, (particularly below 30
kcal/kg FFM/day) was associated with
impairments of a variety of body
functions.
10
Low EA may occur from
insufcient EI, high TEE, or a combi-
nation 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
FROM THE ACADEMY
504 JOURNAL OF THE ACADEMY OF NUTRITION AND DIETETICS March 2016 Volume 116 Number 3
meet energy requirements during a
period of high-volume training or
competition.
10
Example Calculation of EA
60 kg body weight (BW), 20% body
fat, 80% FFM (¼48.0 kg FFM), EI¼2,400
kcal/day, additional energy expendi-
ture from exercise¼500 kcal/day
EA¼(EIeEEE)/FFM¼(2,400e500)
kcal$d/48.0 kg¼39.6 kcal/kg FFM/day
The concept of EA emerged from the
study of the female athlete triad (Triad),
which started as a recognition of the
interrelatedness of clinical issues with
disordered eating, menstrual dysfunc-
tion, 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,
neuropsychiatric, musculoskeletal, and
cardiovascular dysfunction.
11
Indeed, an
extension of the Triad has been pro-
posedthe Relative Energy Deciency
in Sport (RED-S)as an inclusive
description of the entire cluster of
physiologic complications observed in
male and female athletes who consume
energy intakes that are insufcient in
meeting the needs for optimal body
function once the energy cost of exercise
has been removed.
12
Specically, health
consequences of RED-S may negatively
affect menstrual function; bone health;
and endocrine, metabolic, hematologi-
cal, growth and development, psycho-
logical, cardiovascular, gastrointestinal,
and immunological systems. Potential
performance effects of RED-S may
include decreased endurance, increased
injury risk, decreased training response,
impaired judgment, decreased coordi-
nation, decreased concentration, irrita-
bility, depression, decreased glycogen
stores, and decreased muscle strength.
12
It is now also recognized that impair-
ments 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
energy balance or weight loss; indeed, if
a reduction in EA is associated with a
reduction in RMR, it may produce a new
steady-state of energy balance or weight
stability at a lowered energy intake that
is insufcient to provide for healthy
body function.
Regardless of the terminology, it is
apparent that low EA in male and fe-
male athletes may compromise
athletic performance in the short and
long-term. Screening and treatment
guidelines have been established for
management of low EA
11,12
and should
include assessment with the Eating
Disorder Inventory-3 resource
13
or the
Diagnostic and Statistical Manual of
Mental Disorders,fth edition, which
includes changes in eating disorder
criteria.
14
There is evidence that in-
terventions to increase EA are suc-
cessful 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
w40 kcal/kg FFM/day 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 because
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 ath-
letic performance cannot be accurately
predicted solely based on BW and
composition. A single and rigid optimal
body composition should not be rec-
ommended for any event or group of
athletes.
15
Nevertheless, there are re-
lationships between body composition
and sports performance that are
important to consider within an ath-
letespreparation.
In sports involving strength and po-
wer, athletes strive to gain FFM via a
program of muscle hypertrophy at
specied 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, and
weightlifting), competitors typically
target the lowest achievable BW cate-
gory 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 run-
ners and cyclists benet from a low
energy cost of movement and a favor-
able ratio of weight to surface area for
heat dissipation. Team athletes can in-
crease their speed and agility by being
lean, whereas athletes in acrobatic
sports (eg, diving, gymnastics, and
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 aes-
thetics in determining performance
outcomes. Although there are demon-
strated advantages to achieving a
certain body composition, athletes may
feel pressure to strive to achieve unre-
alistically 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 perfor-
mance, and disordered eating patterns
have also been observed in these sport
scenarios.
15,18
Nevertheless, there are scenarios in
which an athlete will enhance his or
her health and performance by
reducing BW or body fat as part of a
periodized strategy. Ideally, this occurs
within a program that gradually ach-
ieves an individualized optimal body
composition over the athletes athletic
career, and allows weight and body fat
to track within a suitable range within
the annual training cycle.
18
The pro-
gram should also include avoiding sit-
uations 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
FROM THE ACADEMY
March 2016 Volume 116 Number 3 JOURNAL OF THE ACADEMY OF NUTRITION AND DIETETICS 505
fat that 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 ath-
letes 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 Composi-
tion Assessment. Techniques used to
assess athlete body composition
include dual energy x-ray absorptiom-
etry (DXA), hydrodensitometry, air
displacement plethysmography, skin-
fold measurements, and single and
multifrequency bioelectrical imped-
ance analysis. Although DXA is quick
and noninvasive, issues around cost,
accessibility, and exposure to a small
radiation dose limit its utility, par-
ticularly for certain populations.
20
When undertaken according to stan-
dardized protocols, DXA has the lowest
standard error of estimate, whereas
skinfold measures have the highest; air
displacement plethysmography (Bod-
Pod, Life Measurement, Inc) provides
an alternative method that is quick and
reliable, but may underestimate body
fat by 2% to 3%.
20
Skinfold measure-
ment and other anthropometric data
serve as an excellent surrogate mea-
sure of adiposity and muscularity when
proling composition changes in
response to training interventions.
20
However, it should be noted that the
standardization of skinfold sites, mea-
surement techniques, and calipers vary
around the world. Despite some limi-
tations, this technique remains a pop-
ular method of choice due to
convenience and cost, with informa-
tion being provided in absolute mea-
sures 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 stan-
dardized protocol, and by technicians
with known testeretest reliability.
Where population-specic 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
preassessment protocols. These in-
structions, which include maintaining
a consistent training volume, fasting
status, and hydration from test to
test
20
should be enforced to avoid
compromising the accuracy and reli-
ability of body composition measures.
Body composition should be deter-
mined within a sports program ac-
cording 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 pro-
vided in terms of ranges.
21
Because
body fat content for an individual
athlete will vary over the season and
over the athletes career, goals for body
composition should be set in terms of
ranges that can be appropriately
tracked at critical times. When con-
ducting such monitoring programs, it is
important that the communication of
results with coaches, training staff, and
athletes is undertaken with sensitivity,
that limitations in measurement tech-
nique are recognized, and that care is
taken to avoid promoting an unhealthy
obsession with body composition.
17,18
Sports dietitians have important op-
portunities to work with these athletes
to help promote a healthy body
composition, and to minimize their
reliance on rapid-weight loss tech-
niques and other hazardous practices
that may result in performance decre-
ments, loss of FFM, 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;
modication of rules or practices
around selection and qualication for
weight classes;
16,19,22
and programs
that identify disordered eating
practices at an early stage for inter-
vention, and where necessary, removal
from play.
18
Principles of Altering Body Com-
position and Weight. Athletes often
need assistance in setting appropriate
short-term and long-term goals, un-
derstanding nutrition 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 benets, including shep-
herding the athlete through short-term
goals and reducing reliance on extreme
techniques and fad diets/behaviors.
There is ample evidence in weight
sensitive and weight-making sports
that athletes frequently undertake
rapid weight loss strategies to gain a
competitive advantage.
20,23,24
Howev-
er, the resultant hypohydration (body
water decit), loss of glycogen stores
and lean mass, and other outcomes of
pathologic behaviors (eg, purging,
excessive training, or 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 restric-
tion and suboptimal nutrition sup-
port.
17
When actual loss of BW 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 maxi-
mize loss of body fat while preserving
muscle mass and other health goals.
Such strategies include achieving a
slight energy decit 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/day) in a
shorter-term (2 week), energy-
restricted diet in athletes was found
to retain muscle mass while losing
weight and body fat.
26
Furthermore,
FFM and performance may be better
preserved in athletes who minimize
weekly weight loss to <1% per week.
25
An individualized diet and training
prescription for weight/fat loss should
be based on assessment of goals, pre-
sent training and nutrition practices,
past experiences, and trial and error.
FROM THE ACADEMY
506 JOURNAL OF THE ACADEMY OF NUTRITION AND DIETETICS March 2016 Volume 116 Number 3
Nevertheless, for most athletes, the
practical approach of decreasing en-
ergy intake by w250 to 500 kcal/day
from their periodized energy needs,
while either maintaining or slightly
increasing energy expenditure, can
achieve progress toward short-term
body composition goals over approxi-
mately 3 to 6 weeks. In some situa-
tions, additional moderate aerobic
training and close monitoring can be
useful.
27
These strategies can be
implemented to help augment the
diet-induced energy decits without
negatively impacting recovery from
sport-specic training. Arranging the
timing and content of meals to sup-
port training nutrition goals and re-
covery 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 unlim-
ited 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
xes, acute dieting, and extreme
weight loss practices.
EAL Question #1 (Figure 1) exam-
ined the effect of negative energy bal-
ance on sport performance, nding
only fair support for an impairment of
physical capacity due to a hypo-
energetic diet in the currently exam-
ined scenarios. However, few studies
have investigated the overlay of factors
commonly seen in practice, including
the interaction of poor dietary quality,
low carbohydrate availability, exces-
sive training, and acute dehydration on
chronic energy restriction. The chal-
lenge 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 FFM
when in energy decit (Figure 1).
Again the literature is limited in
quantity and range to allow denitive
recommendations to be made,
although there is support for the ben-
ets of increased protein intake.
Nutrient Requirements for Sport
Energy Pathways and Training
Adaptations. Guidelines for the
timing and amount of intake of mac-
ronutrients in an athletes diet should
be underpinned by a fundamental un-
derstanding of how training-nutrient
interactions affect energy systems,
substrate availability, and training ad-
aptations. Exercise is fueled by an in-
tegrated series of energy systems that
include nonoxidative (phosphagen and
glycolytic) and aerobic (fat and carbo-
hydrate oxidation) pathways, using
substrates that are both endogenous
and exogenous in origin. ATP and
phosphocreatine (phosphagen system)
provide a rapidly available energy
source for muscular contraction, but
not at sufcient levels to provide a
continuous supply of energy for longer
than w10 seconds. The anaerobic
glycolytic pathway rapidly metabolizes
glucose and muscle glycogen through
the glycolytic cascade and is the pri-
mary pathway supporting high-
intensity exercise lasting 10 to 180
seconds. Because neither the phospha-
gen nor the glycolytic pathway can
sustain energy demands to allow mus-
cles to contract at a very high rate for
longer lasting events, oxidative path-
ways provide the primary fuels for
events lasting longer than w2 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 (oxida-
tive) pathways and less of the anaer-
obic (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 path-
ways and when crossover between
pathways occurs. For a more complete
understanding of fuel systems for
exercise, the reader is directed to spe-
cic texts.
29
An athletes skeletal muscle has a
remarkable plasticity to respond
quickly to mechanical loading and
nutrient availability resulting in
condition-specic metabolic and func-
tional adaptations.
30
These adaptations
inuence performance nutrition rec-
ommendations 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 avail-
ability during the event itself. Adapta-
tions that enhance metabolic exibility
include increases in transport mole-
cules that carry nutrients across
membranes or to the site of their use
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
Although
some muscle substrates (eg, body fat)
are present in relatively large quanti-
ties, others may need to be manipu-
lated according to specic 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 car-
bohydrate stores is relatively limited
and can be acutely manipulated on a
daily basis by dietary intake or even a
single session of exercise.
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 use by both anaerobic and oxida-
tive pathways. Even when working at
the highest intensities that can be
supported by oxidative phosphoryla-
tion, carbohydrate offers advantages
over fat as a substrate because it pro-
vides a greater yield of ATP per vol-
ume of oxygen that can be delivered
to the mitochondria,
3
thus improving
gross exercise efciency.
31
Third, there
is signicant evidence that the per-
formance 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 exer-
cise), whereas depletion of these
stores is associated with fatigue in the
form of reduced work rates, impaired
FROM THE ACADEMY
March 2016 Volume 116 Number 3 JOURNAL OF THE ACADEMY OF NUTRITION AND DIETETICS 507
Table. 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 ne-tuned with individual consideration of
total energy needs, specic 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 optimize availability for specic 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 or undertaking a second session of exercise without adequate
opportunity for refuelling after the rst session).
Light Low intensity or
skill-based activities
3-5 g/kg of athletes
body weight/d
Timing of intake of carbohydrate over the
day may be manipulated to promote high
carbohydrate availability for a specic
session by consuming carbohydrate
before or during the session, or during
recovery from a previous session
Otherwise, as long as total fuel needs are
provided, the pattern of intake may simply
be guided by convenience and individual choice
Athletes should choose nutrient-rich
carbohydrate sources to allow overall
nutrient needs to be met
Moderate Moderate exercise
program (eg, w1 h/d)
5-7 g/kg/d
High Endurance program
(eg, 1-3 h/d moderate to
high-intensity exercise)
6-10 g/kg/d
Very high Extreme commitment
(eg, >4-5 h/d moderate
to high-intensity
exercise)
8-12 g/kg/d
Acute fueling strategies eThese guidelines promote high carbohydrate availability to promote optimal performance during
competition or key training sessions
General fueling
up
Preparation for events
<90 min exercise
7-12 g/kg/24 h as for
daily fuel needs
Athletes may choose carbohydrate-rich
sources that are low in ber/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
>90 min of sustained/
intermittent exercise
36-48 h of 10-12 g/kg
body weight/24 h
Speedy
refueling
<8 h recovery between 2
fuel-demanding sessions
1-1.2 g/kg/h for rst
4 h then resume
daily fuel needs
There may be benets in consuming small,
regular snacks
Carbohydrate-rich foods and drink may help
to ensure that fuel targets are met
Pre-event
fueling
Before exercise >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/ber 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
(continued on next page)
FROM THE ACADEMY
508 JOURNAL OF THE ACADEMY OF NUTRITION AND DIETETICS March 2016 Volume 116 Number 3
skill and concentration, and increased
perception of effort. These ndings
underpin the various performance
nutrition strategies, to be discussed
subsequently, that supply carbohy-
drate before, during, and in the re-
covery between events to enhance
carbohydrate availability.
Finally, recent work has identied
that in addition to its role as a muscle
substrate, glycogen plays important
direct and indirect roles in regulating
the muscles adaptation to training.
32
The amount and localization of
glycogen within muscle cells alters the
physical, metabolic, and hormonal
environment in which the signaling re-
sponses to exercise are exerted. Specif-
ically, starting a bout of endurance
exercise with low muscle glycogen
content (eg, by undertaking a second
training session in the hours after the
prior session has depleted glycogen
stores) produces a coordinated upregu-
lation of the transcriptional and post-
translational responses to exercise. A
number of mechanisms underpin this
outcome, including increasing the ac-
tivity of molecules that have a glycogen
binding domain, increasing free fatty
acid availability, changing osmotic
pressure in the muscle cell, and
increasing catecholamine concentra-
tions.
32
Strategies that restrict exoge-
nous carbohydrate availability (eg,
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 activ-
ities 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 and
p38MAPK), transcription factors (eg,
p53 and PPAR
d
) and transcriptional
coactivators (eg, PGC-1
a
).
33
Deliberate
integration of such training-dietary
strategies (train low) within the per-
iodized training program is becoming a
recognized,
34
although potentially mis-
used,
33
part of sports nutrition practice.
Table. Summary of guidelines for carbohydrate intake by athletes
36
(continued)
Situation
Carbohydrate
targets
Comments on type and timing
of carbohydrate intake
During brief
exercise
<45 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
startsports
1-2.5 h 30-60 g/h Carbohydrate intake provides a source of
fuel for the muscles 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
specialized sports products ranging in form
from liquid to solid may be useful
The athlete should practice to nd a
refuelling plan that suits his or her
individual goals, including hydration needs
and gut comfort
During ultra-
endurance
exercise
>2.5-3 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
FROM THE ACADEMY
March 2016 Volume 116 Number 3 JOURNAL OF THE ACADEMY OF NUTRITION AND DIETETICS 509
Individualized recommendations for
daily intakes of carbohydrate should be
made in consideration of the athletes
training/competition program and the
relative importance of undertaking it
with high or low carbohydrate accord-
ing to the priority of promoting the
performance of high quality exercise vs
enhancing the training stimulus or
adaptation, respectively. Unfortunately,
we lack sophisticated information on
the specic substrate requirements of
many of the training sessions under-
taken by athletes; therefore, we must
rely on guesswork, supported by in-
formation on work requirements of
exercise from technologies such as
consumer-based 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 desig-
nated training or competition sessions
can be provided according to the ath-
letes body size (a proxy for the size of
muscle stores) and the characteristics
of the session (see the Table). The
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. Never-
theless, these fueling practices are also
important for supporting the high-
quality workouts within the perio-
dized training program. Furthermore, it
is intuitive that they add value in ne-
tuning intended event eating strate-
gies, and for promoting adaptations
such as gastrointestinal tolerance and
enhanced intestinal absorption
37
that
allow competition strategies to be fully
effective. During other sessions of the
training program, it may be less
important to achieve high carbohy-
drate 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 car-
bohydrate 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 prox-
imity without opportunity for refueling
between sessions).
38
Specic questions examined via the
evidence analysis on carbohydrate
needs for training are summarized in
the Table and show good evidence that
neither the glycemic load nor glycemic
index of carbohydrate-rich meals affects
the metabolic nor performance out-
comes of training once 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
benets to performance outcomes are
currently unclear (Figure 1,Question
#10). This possibly relates to the limi-
tations of the few available studies in
which poor periodization of this tactic
within the training program has meant
that any advantages to training adapta-
tions have been counteracted by the
reduction in training intensity and
quality associated with low carbohy-
drate variability. Therefore, a more so-
phisticated approach is needed to
integrate this training/nutrient interac-
tion into the larger training program.
33
Finally, although there is support for
consuming multiple forms of carbohy-
drate which 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 proteins
39,40
as well as enhancing structural
changesinnonmuscletissuessuchas
tendons
41
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 provi-
sion of an exogenous source of amino
acids for incorporation into new pro-
teins.
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
Recommended Dietary Allowance
(RDA)
39
to maximize metabolic adap-
tation to training.
40
Although classical nitrogen balance
work has been useful for determining
protein requirements to prevent de-
ciency in sedentary humans in energy
balance,
45
athletes do not meet this
prole and achieving nitrogen balanceis
secondary to an athlete with the pri-
mary goal of adaptation to training and
performance improvement.
40
The
modern view for establishing recom-
mendations for protein intake in ath-
letes extends beyondthe DRIs. Focus has
clearly shifted to evaluating the benets
of providing enough protein at optimal
times to support tissues with rapid
turnover and augment metabolic adap-
tations initiated by training stimulus.
Future research will further rene rec-
ommendations directed at total daily
amounts, timing strategies, quality of
protein intake, and provide new rec-
ommendations 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/
day. Higher intakes may be indicated for
short periods during intensied training
or when reducing energy intake.
26,39
Daily protein intake goals should be
met with a meal plan providing a reg-
ular 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
exible adjustments with periodized
training and experience.
46,47
Although
general daily ranges are provided, in-
dividuals should no longer be solely
categorized as strength or endur-
ance athletes and provided with static
daily protein intake targets. Rather,
FROM THE ACADEMY
510 JOURNAL OF THE ACADEMY OF NUTRITION AND DIETETICS March 2016 Volume 116 Number 3
guidelines should be based around
optimal adaptation to specicsessions
of training/competition within a perio-
dized program, underpinned by an
appreciation of the larger context of
athletic goals, nutrient needs, energy
considerations, and food choices. Re-
quirements can uctuate based on
trainedstatus (eg, experienced ath-
letes requiring less), training (eg, ses-
sions involving higher frequency and
intensity, or a new training stimulus at
higher end of protein range), carbohy-
drate availability, and most importantly,
energy availability.
46,48
The consump-
tion 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 oc-
curs as a result of injury, elevated pro-
tein intakes as high as 2.0 g/kg/day
or higher
26,50
when spread over the
day may be advantageous in prevent-
ing FFM loss.
39
More detailed reviews
of factors that inuence changing pro-
tein 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 opti-
mizedinresponsetoexercisebythe
consumption of high biological value
protein, providing w10 g essential
amino acids in the early recovery
phase (0 to 2 hours after exercise).
40,53
This translates to a recommended
protein intake of 0.25 to 0.3 g/kg BW
or 15 to 25 g protein across the typical
range of athlete body sizes, although
the guidelines may need to be ne-
tuned for athletes at extreme ends of
the weight spectrum.
54
Higher doses
(ie, >40 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 func-
tional change. Whereas protein
timing affects MPS rates, the magni-
tude of mass and strength changes
over time are less clear.
56
However,
longitudinal training studies currently
suggestthatincreasesinstrength
and muscle mass are greatest with
immediatepostexerciseprovisionof
protein.
57
Whereas traditional protein intake
guidelines focused on total protein
intake over the day (grams per kilo-
gram), newer recommendations now
highlight that the muscle adaptation to
training can be maximized by ingesting
these targets as 0.3 g/kg BW after key
exercise sessions and every 3 to 5
hours over multiple meals.
47,54,58
Question #8 (Figure 1) summarizes
the weight of the current literature
of consuming protein on protein-
specic metabolic responses during
recovery.
Optimal protein sources. High-qual-
ity 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 af-
ter resistance exercise is effective in
increasing muscle strength and favor-
able changes in body composi-
tion.
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 uid-based dairy
foods.
62
However, further studies are
warranted to assess other intact high-
quality protein sources (eg, egg, beef,
pork, and concentrated vegetable pro-
tein) and mixed meals on the stimula-
tion of mammalian target of rapamycin
(mTOR) 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 impor-
tant to conduct a thorough assessment
of the athletes specic nutrition goals
when considering protein supple-
ments. Recommendations regarding
protein supplements should be con-
servative 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, essen-
tial elements of cell membranes, and
facilitation of the absorption of fat-
soluble vitamins. The Dietary Guide-
lines for Americans
8
and Eating Well
with Canadas Food Guide
63
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 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 sub-
strate that is both relatively plentiful
and increased in availability to the
muscle as a result of endurance
training. However, exercise-induced
adaptations do not appear to maxi-
mize oxidation rates because they can
be further enhanced by dietary stra-
tegies such as fasting; acute pre-
exercise intake of fat; and chronic
exposure to high-fat, low-carbohy-
drate diets.
3
Although there has been
historical
64
and recently revived
65
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/perfor-
mance achieved by diets or strategies
promoting high carbohydrate availabil-
ity at moderate intensities,
64
whereas
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 war-
ranted both in view of the current dis-
cussions
65
and the failure of current
studies to include an adequate con-
trol diet that includes contemporary
periodized dietary approaches.
68
Although specic scenarios may exist
where high-fat diets may offer some
benets or at least the absence of
disadvantages for performance, in gen-
eral they appear to reduce rather than
enhance metabolic exibility by
reducing carbohydrate availability and
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March 2016 Volume 116 Number 3 JOURNAL OF THE ACADEMY OF NUTRITION AND DIETETICS 511
capacity to use carbohydrate effectively
as an exercise substrate. Therefore,
competitive athletes would be unwise
to sacrice 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 BW or improve body
composition. Athletes should be
discouraged from chronic imple-
mentation 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 well-chosen 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 per-
formance 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 compro-
mise the achievement of body compo-
sition goals. Research in this area is
fraught with study design concerns
that limit direct translation to athletes.
Available evidence warns against
intake of signicant amounts of alcohol
during the pre-exercise period and
during training due to the direct nega-
tive 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 into-
xication or hangover are no longer
present. In the postexercise 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
antidiuretic hormone,
72
and impairing
the MPS desired for adaptation and
repair.
69,73,74
In cold environments,
alcohol consumption increases periph-
eral vasodilation resulting in core tem-
perature dysregulation
75
and there are
likely to be other effects on body func-
tion such as disturbances in acid-base
balance and cytokine-prostaglandin
pathways, and compromised glucose
metabolism and cardiovascular func-
tion.
76
Binge drinking may indirectly
affect recovery goals due to inattention
to guidelinesfor recovery. Binge drinking
is also associated with high-risk behav-
iors leading to accidents and antisocial
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
during the postexercise period when
issues of recovery and injury repair are
apriority.
Micronutrients. Exercise stresses
many of the metabolic pathways in
which micronutrients are required, and
training may result in muscle bio-
chemical 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 suboptimal
amounts of micronutrients and benet
from micronutrient supplementa-
tion.
77
This occurs most frequently in
the case of calcium, vitamin D, iron,
and some antioxidants.
78-80
Single-
micronutrient supplements are gener-
ally only appropriate for correction of
a clinically dened medical reason
(eg, iron supplements for iron de-
ciency anemia [IDA]).
Micronutrients of key interest:
Iron. Iron deciency, 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 (approxi-
mately 6 mg iron is consumed per
w1,000 kcal).
82
Periods of rapid
growth, training at high altitudes,
menstrual blood loss, foot-strike he-
molysis, blood donation, or injury can
negatively inuence iron status.
79,81
Some athletes in intense training may
also have increased iron losses in
sweat, urine, feces, and from intravas-
cular hemolysis.
Regardless of the etiology, a
compromised iron status can nega-
tively inuence 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, >18 mg for women
and >8 mg for men).
81,85
Athletes with IDA should seek clin-
ical follow-up, with therapies,
including oral iron supplementation,
86
improvements in diet, and a possible
reduction in activities that inuence
iron loss (eg, blood donation or a
reduction in weight-bearing training to
lessen erythrocyte hemolysis).
87
The
intake of iron supplements in the
period immediately after strenuous
exercise is contraindicated because
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 advan-
tageous to begin nutrition intervention
before IDA develops.
78,81
Athletes who
are concerned about iron status or have
iron deciency 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 and
nonheme ironþvitamin C foods) as the
rst line of defense. Although there is
some evidence that iron supplements
can achieve performance improve-
ments 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 he-
modilution, known as dilutional or
FROM THE ACADEMY
512 JOURNAL OF THE ACADEMY OF NUTRITION AND DIETETICS March 2016 Volume 116 Number 3
sports anemia, and may not respond to
nutrition intervention. These changes
appear to be a benecial adaptation to
aerobic training and do not negatively
inuence performance.
79
There is no
agreement on the serum ferritin level
that corresponds to a problematic
level of iron depletion/deciency, with
various suggestions ranging from <10
to <35 ng/mL.
86
A thorough clinical
evaluation in this scenario is war-
ranted because ferritin is an acute-
phase protein that increases with
inammation, but in the absence of
inammation, still serves as the best
early indicator of compromised iron
status. Other markers of iron status
and other issues in iron metabolism
(eg, the role of hepcidin) are currently
being explored.
88
Micronutrients of key interest:
Vitamin D. Vitamin D regulates cal-
cium and phosphorus absorption and
metabolism, and plays a key role in
maintaining bone health. There is also
emerging scientic interest in the bio-
molecular role of vitamin D in skeletal
muscle
90
where its role in mediating
muscle metabolic function
91
may have
implications for supporting athletic
performance. A growing number of
studies have documented the relation-
ship between vitamin D status and
injury prevention,
92
rehabilitation,
93
improved neuromuscular function,
94
increased type II muscle ber size,
94
reduced inammation,
93
decreased
risk of stress fracture,
92,95
and acute
respiratory illness.
95
Athletes who live at latitudes >35th
parallel or who primarily train and
compete indoors are likely at higher
risk for vitamin D insufciency (25(OH)
D¼20 to 30 ng/mL [50 to 75 nmol/L])
and deciency (25(OH) D <20 ng/mL
[<50 nmol/L]). Other factors and life-
style habits such as dark complexion,
high body fat content, undertaking of
training in the early morning and eve-
ning when ultraviolet B light (UVB)
levels are low, and aggressive blocking
of UVB exposure (eg, clothing, equip-
ment, and screening/blocking lotions)
increase the risk for insufciency and
deciency.
93
Because athletes tend to
consume little vitamin D from the
diet
93
and dietary interventions alone
have not been shown to be a reliable
means to resolve insufcient status,
96
supplementation above the current
RDA and/or responsible UVB exposure
may be required to maintain sufcient
vitamin D status. A recent study of
National Collegiate Athletic Association
Division 1 swimmers and divers re-
ported that athletes who started at
52 ng/mL (130 nmol/L) and received
daily doses of 4,000 IU vitamin D (100
m
g) were able to maintain sufcient
status over 6 months (mean
change þ1 ng/mL [þ2.5 nmol/L]),
whereas athletes receiving placebo
experienced a mean loss of 20 ng/mL
[50 nmol/L].
97
Unfortunately, deter-
mining vitamin D requirements for
optimal health and performance is a
complex process. Vitamin D blood
levels from 32 ng/mL (80 nmol/L) and
up to 40 ng/mL (100 nmol/L)
93
to 50
ng/mL (125 nmol/L)
94
have been
recognized as prudent goals for
optimal training-induced adaptation.
Although proper assessment and
correction of deciency is likely vital
to athlete well-being and athletic suc-
cess, current data do not support
vitamin D as an ergogenic aid for ath-
letes. Empirical data are still needed to
elucidate the direct role of vitamin D in
musculoskeletal health and function
to help rene recommendations for
athletes. Until then, athletes with a
history of stress fracture, bone or joint
injury, signs of overtraining, muscle
pain or weakness, and a lifestyle
involving low exposure to UVB may
require assessment
98
to determine if
an individualized vitamin D supple-
mentation protocol is required.
Micronutrients of key interest: Cal-
cium. 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 frac-
tures is increased by low energy avail-
ability 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 specic avoidance of dairy
products or other calcium-rich foods.
Calcium supplementation should be
determined after a thorough assess-
ment of usual dietary intake. Calcium
intakes of 1,500 mg/day and 1,500 to
2,000 IU/day vitamin D are needed to
optimize bone health in athletes with
low energy availability or menstrual
dysfunctions.
12
Micronutrients of key interest: Anti-
oxidants. 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 oxida-
tive stress on cells.
101
Acute exercise is
known to increase levels of lipid
peroxide byproducts,
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
benet from antioxidant supplemen-
tation, especially if consuming a diet
high in antioxidant-rich foods. There is
little evidence that antioxidant sup-
plements enhance athletic perfor-
mance
101
and the interpretation of
existing data is confounded by issues of
study design (eg, a large variability in
subject characteristics, training pro-
tocols, and the doses and combinations
of antioxidant supplements as well as
the scarcity of crossover designs).
There is also some evidence that anti-
oxidant supplementation may nega-
tively inuence training adaptations.
103