Exercise and Sport Nutrition Review
I came across this article while doing some research. It's long but because it is a review article it draws from many sources and has a lot of good information.
ISSN EXERCISE & SPORT NUTRITION REVIEW:
RESEARCH & RECOMMENDATIONS
Richard B. Kreider1, Anthony L. Almada2, Jose Antonio3, Craig Broeder4, Conrad Earnest5, Mike
Greenwood1, Thomas Incledon6, Douglas S. Kalman7, Susan M. Kleiner8, Brian Leutholtz1, Lonnie
M. Lowery9, Ron Mendel10, Jeffrey R. Stout11, Darryn S. Willoughby1, Tim N. Ziegenfuss10
Exercise & Sport Nutrition Lab, Baylor University, Waco, TX1; IMAGINutrition, Laguna Nigel,
CA2; Juvalution, Fort Lauderdale, FL3; Department of Biological Sciences, Clinical Exercise
Physiology Program, Benedictine University, Lisle, IL 4; The Cooper Institute, Dallas, TX5; Human
Performance Specialists, Inc., Chandler, AZ6; Miami Research Associates, Miami, FL7;
Department of Medical History and Ethics, University of Washington, Seattle, WA8; Human
Nutrition Laboratory, Department of Nutrition and Dietetics, Kent State University, Kent, OH9;
Ohio Research Group of Exercise Science & Sports Nutrition, Wadsworth, OH10; Department of
Exercise Science and Health Promotion, Florida Atlantic University, Davie, FL11. Sports Nutrition
Review Journal. 1(1):1-44, 2004. Address correspondence to Richard_Kreider@baylor.edu.
Received May 10, 2004/Accepted May 15, 2004/Published (online)
__________________________________________________ ______________________________
ABSTRACT
Sport nutrition is a constantly evolving field with literally thousands of research papers published annually. For this reason, keeping up to date with the literature is often difficult. This paper presents a well-referenced overview of the current state of the science related to how to optimize
training through nutrition. More specifically, this article discusses: 1.) how to evaluate the scientific merit of nutritional supplements; 2.) general nutritional strategies to optimize performance and enhance recovery; and, 3.) our current understanding of the available science behind weight gain, weight loss, and performance enhancement supplements. Our hope is that ISSN members find this review useful in their daily practice and consultation with their clients. Sports Nutrition Review Journal. 1(1):1-44, 2004.
Key Words: sport nutrition, dietary supplements, ergogenic aids, weight gain, weight loss
__________________________________________________ ______________________________
INTRODUCTION
Sport nutrition professionals need to know
how to evaluate the scientific merit of articles
and advertisements about exercise and
nutrition products so they can separate
marketing hype from scientifically based
training and nutritional practices. In order to
help educate ISSN members about sport
nutrition, we have updated a letter to the
Editor (PEP Online. 6(10), 2003) which
represents a compilation of Dr. Kreider’s
published work in this area for the Sport
Nutrition Review Journal’s inaugural issue.
This paper provides an overview of: 1.) what
are ergogenic aids and dietary supplements;
2.) how dietary supplements are legally
regulated; 3.) how to evaluate the scientific
merit of nutritional supplements; 4.) general
nutritional strategies to optimize performance
and enhance recovery; and, 5.) an overview of
our current understanding of the ergogenic
value weight gain, weight loss, and
performance enhancement supplements. We
have also categorized nutritional supplements
into apparently effective, possibly effective,
too early to tell, and apparently ineffective as
well as describes our general approach to
educating athletes about sport nutrition.
While some may not agree with all of our
interpretations of the literature and/or
categorization of a particular supplement and
some classifications may change over time as
more research is forthcoming, these
interpretations are based on the current
available scientific evidence and have been
well received within the broader scientific
community. Our hope is that ISSN members
find this information useful in their daily
practice and consultation with their clients.
WHAT IS AN ERGOGENIC AID?
An ergogenic aid is any training technique,
mechanical device, nutritional practice,
pharmacological method, or psychological
technique that can improve exercise
performance capacity and/or enhance training
adaptations 1, 2. This includes aids that may
help prepare an individual to exercise,
improve the efficiency of exercise, and/or
enhance recovery from exercise. Ergogenic
aids may also allow an individual to tolerate
heavy training to a greater degree by helping
them recover faster or help them stay healthy
during intense training. Although this
definition seems rather straightforward, there
is considerable debate regarding the ergogenic
value of various nutritional supplements.
Some sport nutrition specialists only consider
a supplement ergogenic if studies show that
the supplement significantly enhances
exercise performance (e.g., helps you run
faster, lift more weight, and/or perform more
work during a given exercise task). On the
other hand, some feel that if a supplement
helps prepare an athlete to perform or
enhances recovery from exercise, it has the
potential to improve training adaptations and
therefore should be considered ergogenic. In
our view, one should take a broader view
about the ergogenic value of supplements.
While we are interested in determining the
performance enhancement effects of a
supplement on a single bout of exercise, we
also realize that one of the goals of training is
to help people tolerate training to a greater
degree. People who tolerate training better
usually experience greater gains from training
over time. Consequently, employing
nutritional practices that help prepare people
to perform and/or enhance recovery from
exercise should also be viewed as ergogenic.
WHAT ARE DIETARY SUPPLEMENTS
AND HOW ARE THEY REGULATED?
According to the Food and Drug
Administration (FDA), dietary supplements
were regulated in the same manner as food
prior to 1994 3. Consequently, the
manufacturing processes, quality, and
labeling of supplements were monitored by
FDA. However, many people felt that the
FDA was too restrictive in regulating dietary
supplements. As a result, Congress passed
the Dietary Supplement Health and Education
Act (DSHEA) in 1994 which placed dietary
supplements in a special category of "foods".
In October 1994, DSHEA was signed into law
by President Clinton. The law defined a
"dietary supplement" as a product taken by
mouth that contains a "dietary ingredient"
intended to supplement the diet. “Dietary
ingredients" may include vitamins, minerals,
herbs or other botanicals, amino acids, and
substances (e.g., enzymes, organ tissues,
glandulars, and metabolites). Dietary
supplements may also be extracts or
concentrates from plants or foods. Dietary
supplements are typically sold in the form of
tablets, capsules, soft gels, liquids, powders,
and bars. Products sold as dietary
supplements must be clearly labeled as a
dietary supplement.
According to DSHEA, dietary supplements
are not drugs. Dietary supplement ingredients
that were sold prior to 1994 are therefore not
required to be shown to be safe and/or
effective in clinical trials prior to being
approved for sale by the FDA. However, new
dietary supplement ingredients introduced
after 1994 must undergo pre-market review
for safety data by the FDA before it can be
legally sold. Supplement companies are
responsible for determining that the dietary
supplements it manufactures or distributes are
safe and that any representations or claims
made about them are substantiated by
Sports Nutrition Review Journal. 1 (1):1-44, 2004. (www.sportsnutritionsociety.org)
3
adequate evidence to show that they are not
false or misleading. Because of this, DSHEA
requires supplement manufacturers to include
on the label that “This statement has not been
evaluated by the FDA. This product is not
intended to diagnose, treat, cure, or prevent
any disease". According to the 1994
Nutrition Labeling and Education Act
(NELA), the FDA has the ability to review
and approve health claims for dietary
supplements and foods. However, since the
law was passed, it has only reviewed a few
claims. The delay in reviewing health claims
of dietary supplements resulted in a law suit
filed by Pearson & Shaw et al v. Shalala et al
in 1993. After years of litigation, U.S. Court
of Appeals for the District of Columbia
Circuit ruled in 1999 that qualified health
claims may now be made about dietary
supplements with approval by FDA as long as
the statements are truthful and based on
science. Supplement companies wishing to
make health claims about supplements can
submit research evidence to the FDA for
approval. Additionally, they must submit an
Investigation of New Drug (IND) application
to FDA if a research study on a nutrient is
designed to treat an illness and/or medical
affliction and/or the company hopes to one
day obtain approval for making a qualified
health claim if the outcome of the study
supports the claim. Studies investigating
structure and function claims, however, do
not need to be submitted to the FDA as an
IND.
Manufacturers and distributors of dietary
supplements are not currently required to
record, investigate or forward to FDA any
reports they receive on injuries or illnesses
that may be related to the use of their
products. However, the FDA and other groups
have established phone hotlines and online
adverse event monitoring systems to report
problems they believe may be a result of
taking dietary supplements. While these
reports are unsubstantiated, can be influenced
by media attention to a particular supplement,
and do not necessarily show a cause and
effect, they are used by the FDA to monitor
trends and “signals” that may suggest a
problem. Once a dietary supplement product
is marketed, the FDA has the responsibility
for showing that a dietary supplement is
unsafe before it can take action to restrict the
product's use or removal from the
marketplace. The Federal Trade Commission
(FTC) is responsible to make sure
manufacturers are truthful regarding claims
they make about dietary supplements. The
FDA has the power to remove supplements
from the market if it has sufficient scientific
evidence to show the supplement is unsafe.
Additionally, the FTC has the power to act
against companies who make false and/or
misleading marketing claims about a specific
product. This includes acting against
companies if the ingredients found in the
supplement do not match label claims. While
this does not ensure the safety of dietary
supplements, it does provide a means for
governmental oversight of the dietary
supplement industry if adequate resources are
provided to enforce DSHEA. Since inception
of DSHEA, the FDA has required a number
of supplement companies to submit evidence
showing safety of their products and acted to
remove a number of products sold as dietary
supplements from sale in the U.S. due to
safety concerns. Additionally, the FTC has
acted against a number of supplement
companies for misleading advertisements
and/or structure and function claims.
As can be seen, although some argue that the
dietary supplement industry is “unregulated”
and/or may have suggestions for additional
regulation, manufacturers of dietary
supplements must adhere to a number of
federal regulations before a product can go to
market. Further, they must have evidence that
the ingredients sold in their supplements are
generally safe if requested to do so by the
FDA. For this reason, over the last 10-15
years, most quality supplement companies
have employed a team of researchers (many
of whom are MS or PhD prepared exercise
physiologists or sport nutrition specialists)
who help educate the public about nutrition
and exercise, provide input on product
Sports Nutrition Review Journal. 1 (1):1-44, 2004. (www.sportsnutritionsociety.org)
4
development, conduct preliminary research on
products, and/or assist in coordinating
research trials conducted by independent
research teams (e.g., university based
researchers or clinical research sites). They
also consult with marketing teams with the
responsibility to ensure structure and function
claims do not misrepresent results of research
findings. This has increased job opportunities
for sport nutrition specialists as well as
enhanced opportunities for external funding
for research groups interested in exercise
nutrition research. While it is true that some
companies use borrowed science, suppress
negative findings, and/or exaggerate results
from research studies, the trend in the
nutrition industry is to develop scientifically
sound supplements. This trend toward greater
research support is the result of: 1.) attempts
to honestly and accurately inform the public
about results; 2.) efforts to have data to
support safety and efficacy on products for
FDA and the FTC; and/or, 3.) to provide
scientific evidence to support advertising
claims and increase sales. This trend is due
in large part to greater scrutiny from the FDA
and FTC as a result of increased consumer
expectations and political pressure to ensure
that companies sell quality products that have
been shown to be safe and effective in clinical
trials. In our experience, companies who
adhere to these ethical standards prosper
while those who do not struggle to adhere to
FDA and FTC guidelines and lose consumer
confidence. When this occurs, companies are
often sued by consumers and/or are forced out
of business because ultimately the consumer
has the final word on whether a supplement or
supplement company is credible or not.
HOW TO EVALUATE NUTRITIONAL
ERGOGENIC AIDS
When you evaluate the ergogenic value of a
nutritional supplement or training
device/method, we recommend that you go
through a process of evaluating the validity
and scientific merit of claims made. This can
be accomplished by evaluating the theoretical
rationale behind the supplement/technique
and determining whether there is any wellcontrolled
data showing the
supplement/technique works. Training
devices and supplements based on sound
scientific rationale with supportive research
showing effectiveness may be worth trying
and/or recommending. However, those based
on unsound scientific rationales and/or little
to no data supporting the ergogenic value for
people involved in intense training may not.
The sport nutrition specialist should be a
resource to help their clients interpret the
scientific and medical research that may
impact on their welfare and/or help them train
more wisely. The following are the questions
we recommend asking when evaluating the
potential ergogenic value of a supplement.
Does The Theory Make Sense?
Most supplements that have been marketed to
improve health and/or exercise performance
are based on theoretical applications derived
from basic and/or clinical research studies.
Based on these preliminary studies, a training
device or supplement is often marketed to
people proclaiming the benefits observed in
these basic research studies. Although the
theory may sound good, critical analysis of
the theory often reveals flaws in scientific
logic and/or that the claims made don’t quite
match up with the literature cited. If you do
your homework, you can discern whether a
supplement has been based on sound
scientific evidence or not. To do so, we
suggest you read reviews about the training
method, nutrient, and/or supplement from
researchers who have been intimately
involved in this line of research and/or consult
reliable references about nutritional and
herbal supplements 4-8. We also suggest
doing a search on the nutrient/supplement on
the National Library of Medicine’s Pub Med
Online 9. A quick look at these references
will often help you know whether the theory
is plausible or not. In our experience,
proponents of ergogenic aids often overstate
claims made about training devices and/or
nutritional supplements while opponents of
nutritional supplements and ergogenic aids
Sports Nutrition Review Journal. 1 (1):1-44, 2004. (www.sportsnutritionsociety.org)
5
are either unaware and/or ignorant of research
supporting their use. The sport nutrition
specialist has the responsibility to know the
literature and/or search available data bases to
know whether there is merit or not to a
proposed ergogenic aid.
Is There Any Scientific Evidence Supporting
The Ergogenic Value?
The next question suggest asking is whether
there is any well-controlled data showing the
proposed ergogenic aid works as claimed in
athletes or people involved in training. The
first place we look is the list of references
cited in marketing material supporting their
claims. We look to see if the abstracts or
articles cited are general references or specific
studies that have evaluated the efficacy of the
nutrient/supplement. We then critically
evaluate the abstracts and articles by asking a
series of questions.
�� Are the studies simply basic research done
in animals/clinical populations or have the
studies been conducted on athletes?
Studies reporting improved performance
in rats may be insightful but research
conducted on athletes is much more
convincing.
�� Were the studies well controlled? For
ergogenic aid research, the study should
be a placebo controlled, double blind, and
randomized clinical trail if possible. This
means that neither the researcher’s nor the
subject’s were aware which group
received the supplement or the placebo
during the study and that the subjects were
randomly assigned into the placebo or
supplement group. At times, supplement
claims have been based on poorly
designed studies (i.e., small groups of
subjects, no control group, use of
unreliable tests, etc) and/or testimonials
which may make interpretation much
more difficult. Studies that are well
controlled clinical trials provide stronger
evidence as to the potential ergogenic
value than those that are not well
controlled.
�� Do the studies report statistically
significant results or are claims being
made on non-significant means or trends
reported? Appropriate statistical analysis
of research results allows for an unbiased
interpretation of data. Although studies
reporting statistical trends may be of
interest and lead researchers to conduct
additional research, studies reporting
statistically significant results are
obviously more convincing. With this
said, sport nutrition specialist must be
careful not to commit type II statistical
error (i.e., indicating that no differences
were observed when a true effect was seen
but not detected statistically). Since many
studies on ergogenic aids (particularly in
high level athletes) evaluate small
numbers of subjects, results may not reach
statistical significance even though large
mean changes were observed. In these
cases, additional research is warranted to
further examine the potential ergogenic
aid before conclusions can be made.
�� Do the results of the studies cited match
the claims made about the supplement?
It is not unusual for marketing claims to
greatly exaggerate the results found in the
actual studies. Therefore, you should
compare results observed in the studies to
marketing claims. Reputable companies
accurately report results of studies so that
consumers can make informed decisions
about whether to try a product or not.
�� Were results of the study presented at a
reputable scientific meeting and/or
published in a peer-reviewed scientific
journal? At times, claims are based on
research that has either never been
published or only published in an obscure
journal. The best research is typically
presented at respected scientific meetings
and/or published in reputable peerreviewed
journals.
�� Have the research findings been replicated
at several different labs? The best way to
know an ergogenic aid works is to see that
results have been replicated in several
studies preferably by a number of
researchers. The most reliable ergogenic
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6
aids are those in which a number of
studies, conducted at different labs, have
reported similar results.
Is The Supplement Legal And Safe?
The final question we ask is whether the
supplement is legal and/or safe. Some
athletic associations have banned the use of
various nutritional supplements (e.g.,
prohormones, ephedra, etc). Obviously, if the
supplement is banned, the sport nutrition
specialist should discourage its use. In
addition, many supplements have not been
studied for long-term safety. People who
consider taking nutritional supplements
should be well aware of the potential side
effects so that they can make an informed
decision regarding whether to use a
supplement or not. Additionally, they should
consult with a knowledgeable physician to see
if there are any underlying medical problems
that may contraindicate use. When evaluating
the safety of a supplement, we suggest
looking to see if any side effects have been
reported in the scientific or medical literature.
In particular, we suggest determining how
long a particular supplement has been studied,
the dosages evaluated, and whether any side
effects were observed. We also recommend
consulting the PDR for nutritional
supplements and herbal supplements to see if
any side effects have been reported and/or
there are any known drug interactions. If no
side effects have been reported in the
scientific/medical literature, we generally will
view the supplement as safe for the length of
time and dosages evaluated.
CLASSIFYING AND CATEGORIZING
SUPPLEMENTS
Dietary supplements may contain
carbohydrate, protein, fat, minerals, vitamins,
herbs, and/or various plant/food extracts.
Supplements can generally be classified as
convenience supplements (e.g., energy bars,
meal replacement powders, ready to drink
supplements) designed to provide a
convenient means of meeting caloric needs
and/or managing caloric intake, weight gain
supplements, weight loss supplements, and
performance enhancement supplements.
Based on the above criteria, we generally
categorize nutritional supplements into the
following categories:
I. Apparently Effective. Supplements that
help people meet general caloric needs
and/or the majority of research studies
show is effective and safe.
II. Possibly Effective. Supplements that
initial studies support the theoretical
rationale but that more research is needed
to determine how the supplement may
affect training and/or performance.
III. Too Early To Tell. Supplements that the
theory may make sense but there is
insufficient research to support the use at
this time.
IV. Apparently Ineffective. Supplements
that the theoretical rationale makes little
scientific sense and/or research has clearly
shown to be ineffective.
When a sport nutrition specialist councils
people who train, they should first evaluate
their diet and training program. They should
make sure that the athlete is eating an energy
balanced, nutrient dense diet and that they are
training intelligently. This is the foundation
to build a good program. Following this, we
recommend that they generally only
recommend supplements in category I. If
someone is interested in trying supplements in
category II, they should make sure that they
understand that these supplements are more
experimental and that they may or may not
see the type of results claimed. We
recommend discouraging people from trying
supplements in category III because there
isn’t enough data available on whether they
work or not. However, if someone wants to
try one of these supplements, they should
understand that although there is some
theoretical rationale, there is little evidence to
support use at this time. Obviously, we do
not support athletes taking supplements in
categories IV. We believe that this approach
is a more scientifically supportable and
Sports Nutrition Review Journal. 1 (1):1-44, 2004. (www.sportsnutritionsociety.org)
7
balanced view than simply dismissing the use
of all dietary supplements out of hand.
GENERAL DIETARY GUIDELINES
FOR ACTIVE INDIVIDUALS
A well-designed diet that meets energy intake
needs and incorporates proper timing of
nutrients is the foundation upon which a good
training program can be developed. Research
has clearly shown that athletes that do not
ingest enough calories and/or do not consume
enough of the right type of macronutrients
may impede training adaptations while
athletes who consume a good diet can help
the body adapt to training. Moreover,
maintaining an energy deficient diet during
training may lead to loss of muscle mass,
increased susceptibility to illness, and
increase prevalence of overreaching and/or
overtraining. Incorporating good dietary
practices as part of a training program is one
way to help optimize training adaptations and
prevent overtraining. The following
overviews energy intake and major nutrient
needs of active individuals.
Energy Intake
The first component to optimize training and
performance through nutrition is to ensure the
athlete is consuming enough calories to offset
energy expenditure 1, 10-12. People who
participate in a general fitness program (e.g.,
exercising 30 - 40 minutes per day, 3 times
per week) can generally meet nutritional
needs following a normal diet (e.g., 1,800 –
2,400 kcals/day or about 25 - 35 kcals/kg/day
for a 50 – 80 kg individual) because their
caloric demands from exercise are not too
great (e.g., 200 – 400 kcals/session) 1.
However, athletes involved in moderate levels
of intense training (e.g., 2-3 hours per day of
intense exercise performed 5-6 times per
week) or high volume intense training (e.g.,
3-6 hours per day of intense training in 1-2
workouts for 5-6 days per week) may expend
600 – 1,200 kcals or more per hour during
exercise 1, 13. For this reason, their caloric
needs may approach 50 – 80 kcals/kg/day
(2,500 – 8,000 kcals/day for a 50 – 100 kg
athlete). For elite athletes, energy
expenditure during heavy training or
competition may be enormous. For example,
energy expenditure for cyclists to compete in
the Tour de France has been estimated as high
as 12,000 kcals/day (150 - 200 kcals/kg/d for
a 60 – 80 kg athlete) 13-15. Additionally,
caloric needs for large athletes (i.e., 100 – 150
kg) may range between 6,000 – 12,000
kcals/day depending on the volume and
intensity of different training phases 13.
Although some argue that athletes can meet
caloric needs simply by consuming a wellbalanced
diet, it is often very difficult for
larger athletes and/or athletes engaged in high
volume/intense training to be able to eat
enough food in order to meet caloric needs 1,
11, 13-15. Maintaining an energy deficient diet
during training often leads to significant
weight loss (including muscle mass), illness,
onset of physical and psychological
symptoms of overtraining, and reductions in
performance 12. Nutritional analyses of
athletes’ diets have revealed that many are
susceptible to maintaining negative energy
intakes during training. Susceptible
populations include runners, cyclists,
swimmers, triathletes, gymnasts, skaters,
dancers, wrestlers, boxers, and athletes
attempting to lose weight too quickly 11.
Additionally, female athletes have been
reported to have a high incidence of eating
disorders 11. Consequently, it is important for
the sport nutrition specialist working with
athletes to ensure that athletes are well-fed
and consume enough calories to offset the
increased energy demands of training and
maintain body weight. Although this sounds
relatively simple, intense training often
suppresses appetite and/or alters hunger
patterns so that many athletes do not feel like
eating 11. Some athletes do not like to
exercise within several hours after eating
because of sensations of fullness and/or a
predisposition to cause gastrointestinal
distress. Further, travel and training
schedules may limit food availability and/or
Sports Nutrition Review Journal. 1 (1):1-44, 2004. (www.sportsnutritionsociety.org)
8
the types of food athletes are accustomed to
eating. This means that care should be taken
to plan meal times in concert with training as
well as make sure athletes have sufficient
availability of nutrient dense foods
throughout the day for snacking between
meals (e.g., drinks, fruit, carbohydrate/protein
bars, etc) 1, 10, 11. For this reason, sport
nutritionists’ often recommend that athletes
consume 4-6 meals per day and snack in
between meals in order to meet energy needs.
Use of nutrient dense energy bars and high
calorie carbohydrate/protein supplements
provides a convenient way for athletes to
supplement their diet in order to maintain
energy intake during training.
Carbohydrate
The second component to optimizing training
and performance through nutrition is to
ensure that athletes consume the proper
amounts of carbohydrate, protein and fat in
their diet. Individuals engaged in a general
fitness program can typically meet
macronutrient needs by consuming a normal
diet (i.e., 45-55% carbohydrate [3-5
grams/kg/day], 10-15% protein [0.8 – 1.0
gram/kg/day], and 25-35% fat [0.5 – 1.5
grams/kg/day]). However, athletes involved
in moderate and high volume training need
greater amounts of carbohydrate and protein
in their diet to meet macronutrient needs. For
example, in terms of carbohydrate needs,
athletes involved in moderate amounts of
intense training (e.g., 2-3 hours per day of
intense exercise performed 5-6 times per
week) typically need to consume a diet
consisting of 55-65% carbohydrate (i.e., 5-8
grams/kg/day or 250 – 1,200 grams/day for
50 – 150 kg athletes) in order to maintain
liver and muscle glycogen stores 1, 10.
Research has also shown that athletes
involved in high volume intense training (e.g.,
3-6 hours per day of intense training in 1-2
workouts for 5-6 days per week) may need to
consume 8-10 grams/day of carbohydrate
(i.e., 400 – 1,500 grams/day for 50 – 150 kg
athletes) in order to maintain muscle glycogen
levels 1, 10. This would be equivalent to
consuming 0.5 – 2.0 kg of spaghetti.
Preferably, the majority of dietary
carbohydrate should come from complex
carbohydrates with a low to moderate
glycemic index (e.g., grains, starches, fruit,
maltodextrins, etc). However, since it is
physically difficult to consume that much
carbohydrate per day when an athlete is
involved in intense training, many
nutritionists and sport nutrition specialist
recommend that athletes consume
concentrated carbohydrate juices/drinks
and/or consume high carbohydrate
supplements to meet carbohydrate needs.
While consuming this amount of carbohydrate
is not necessary for the fitness minded
individual who only trains 3-4 times per week
for 30-60 minutes, it is essential for
competitive athletes engaged in intense
moderate to high volume training.
Protein
There has been considerable debate
regarding protein needs of athletes 16-20.
Initially, it was recommended that athletes
do not need to ingest more than the RDA
for protein (i.e., 0.8 to 1.0 g/kg/d for
children, adolescents and adults). However,
research over the last decade has indicated
that athletes engaged in intense training
need to ingest about 1.5 – 2 times the RDA
of protein in their diet (1.5 to 2.0 g/kg/d) in
order to maintain protein balance 16-20. If an
insufficient amount of protein is obtained
from the diet, an athlete will maintain a
negative nitrogen balance which can
increase protein catabolism and slow
recovery. Over time, this may lead to lean
muscle wasting and training intolerance 1, 12.
For people involved in a general fitness
program, protein needs can generally be met
by ingesting 0.8 – 1.0 grams/kg/day of
protein. It is generally recommended that
athletes involved in moderate amounts of
intense training consume 1 – 1.5
grams/kg/day of protein (50 – 225
grams/day for a 50 – 150 kg athlete) while
athletes involved in high volume intense
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9
training consume 1.5 – 2.0 grams/kg/day of
protein (75 – 300 grams/day for a 50 – 150
kg athlete) 21. This protein need would be
equivalent to ingesting 3 – 11 servings of
chicken or fish per day for a 50 – 150 kg
athlete 21. Although smaller athletes
typically can ingest this amount of protein
in their normal diet, larger athletes often
have difficulty consuming this much dietary
protein. Additionally, a number of athletic
populations have been reported to be
susceptible to protein malnutrition (e.g.,
runners, cyclists, swimmers, triathletes,
gymnasts, dancers, skaters, wrestlers,
boxers, etc). Therefore, care should be
taken to ensure that athletes consume a
sufficient amount of quality protein in their
diet in order to maintain nitrogen balance
(e.g., 1.5 - 2 grams/kg/day).
However, it should be noted that not all
protein is the same. Proteins differ based on
the source that the protein was obtained, the
amino acid profile of the protein, and the
methods of processing or isolating the
protein 22. These differences influence
availability of amino acids and peptides that
have been reported to possess biological
activity (e.g., α-lactalbumin, ßlactoglobulin,
glycomacropeptides,
immunoglobulins, lactoperoxidases,
lactoferrin, etc). Additionally, the rate and
metabolic activity of the protein 22. For
example, different types of proteins (e.g.,
casein and whey) are digested at different
rates which directly affect catabolism and
anabolism 22-25. Therefore, care should be
taken not only to make sure the athlete
consumes enough protein in their diet but
also that the protein is high quality. The
best dietary sources of low fat and high
quality protein are light skinless chicken,
fish, egg white and skim milk (casein and
whey) 22. The best sources of high quality
protein found in nutritional supplements is
whey, colostrum, casein, milk proteins and
egg protein 21, 22. Although some athletes
may not need to supplement their diet with
protein and some sport nutrition specialists
may not think that protein supplements are
necessary, suggestions that it is unethical
for an sport nutrition specialist to
recommend that some athletes supplement
their diet with protein in order to meet
dietary protein needs and/or provide
essential amino acids following exercise in
order to optimize protein synthesis is clearly
not supported by the literature.
Fat
The dietary recommendations of fat intake
for athletes are similar to or slightly greater
than those recommended for non-athletes in
order to promote health. Maintenance of
energy balance, replenishment of
intramuscular triacylglycerol stores and
adequate consumption of essential fatty
acids are of greater importance among
athletes and allow for somewhat increased
intake 26. This depends on the athlete’s
training state and goals. For example,
higher-fat diets appear to maintain
circulating testosterone concentrations
better than low-fat diets 27-29. This has
relevance to the documented testosterone
suppression which can occur during
volume-type overtraining 30. Generally, it is
recommended that athletes consume a
moderate amount of fat (approximately 30%
of their daily caloric intake), while increases
up to 50% of kcal can be safely ingested by
athletes during regular high-volume training
26. For athletes attempting to decrease body
fat, however, it has been recommended that
they consume 0.5 to 1 g/kg/d of fat 1. The
reason for this is that some weight loss
studies indicate that people who are most
successful in losing weight and maintaining
the weight loss are those who ingest less
than 40 g/d of fat in their diet 31, 32 although
this is not always the case 33. Certainly, the
type of dietary fat (e.g. n-6 versus n-3;
saturation state) is a factor in such research
and could play an important role in any
discrepancies 34, 35. Strategies to help
athletes manage dietary fat intake include
teaching them which foods contain various
types of fat so that they can make better
Sports Nutrition Review Journal. 1 (1):1-44, 2004. (www.sportsnutritionsociety.org)
10
food choices and how to how to count fat
grams 1, 11.
Strategic Eating and Refueling
In addition to the general nutritional
guidelines described above, research has also
demonstrated that timing and composition of
meals consumed may play a role in
optimizing performance, training adaptations,
and preventing overtraining 1, 10, 36, 37. In this
regard, it takes about 4 hours for carbohydrate
to be digested and begin to be stored as
muscle and liver glycogen. Consequently,
pre-exercise meals should be consumed about
4 to 6 h before exercise 10. This means that if
an athlete trains in the afternoon, breakfast is
the most important meal to top off muscle and
liver glycogen levels. Research has also
indicated that ingesting a light carbohydrate
and protein snack 30 to 60 min prior to
exercise (e.g., 50 g of carbohydrate and 5 to
10 g of protein) serves to increase
carbohydrate availability toward the end of an
intense exercise bout 38, 39. This also serves to
increase availability of amino acids and
decrease exercise-induced catabolism of
protein 36, 38, 39.
When exercise lasts more than one hour,
athletes should ingest glucose/electrolyte
solution (GES) drinks in order to maintain
blood glucose levels, help prevent
dehydration, and reduce the
immunosuppressive effects of intense
exercise 10, 40-45. Following intense
exercise, athletes should consume
carbohydrate and protein (e.g., 1 g/kg of
carbohydrate and 0.5 g/kg of protein) within
30 min after exercise as well as consume a
high carbohydrate meal within two hours
following exercise 1, 36, 37. This nutritional
strategy has been found to accelerate
glycogen resynthesis as well as promote a
more anabolic hormonal profile that may
hasten recovery 46-48. Finally, for 2 to 3
days prior to competition, athletes should
taper training by 30 to 50% and consume
200 to 300 g/d of extra carbohydrate in their
diet. This carbohydrate loading technique
has been shown to supersaturate
carbohydrate stores prior to competition and
improve endurance exercise capacity 1, 10, 37.
Thus, the type of meal and timing of eating
are important factors in maintaining
carbohydrate availability during training
and potentially decreasing the incidence of
overtraining.
