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Nutrition
The Utilization of Nutrients
to Provide the Various
Biological Systems with
Usable Substances
04/2012
d:\Faculty\Allsen\EXSC 468\Winning Edge\EXSC46808Nutrition
181
I.
Nutrition—the utilization of nutrients to provide the various biological systems with usable
substances
A. Read article on Nutrition and Athletic Performance in appendix at the end of this unit, p. 202
II.
Foods
A. Carbohydrates (CHO)
1. Supply a relatively quick and cheap source of energy
2. Provide dietary fiber
3. May provide water when stored carbohydrate (glycogen) is metabolized by the body
a. Approximately 2.7–3.0 grams of water are stored with each gram of glycogen
B. Fats
1. Stored energy
2. Cushioning and insulation
3. Carry fat-soluble vitamins—A, D, E, K
4. Essential role in cellular membrane structure, hormone synthesis, and prostaglandin
formation
C. Protein
1. Build and rebuild tissue
2. Control metabolic reactions
3. 100,000 different proteins in the human body
4. All protein is metabolized from subunits known as amino acids. There are 20 known amino
acids in the human body
5. Essential amino acids—cannot be produced by the human body
6. Complete proteins—contain all of the essential amino acids
7. Incomplete proteins—don’t contain all of the essential amino acids
Summary of the functions of proteins and amino acids in the human metabolism
Form vital constituents of all cells in the body, such as
contractile muscle proteins
Transport various substances in the blood, such as the
Transport function
lipoproteins for conveying triglycerides
Form almost all enzymes in the body to regulate numerous
Enzyme function
diverse physiological processes
Form various hormones, such as insulin; form various
Hormone and
neurotransmitters, or neuropeptides, that function in the
neurotransmitter function
central nervous system, such as serotonin
Form key components of the immune system, such as
Immune function
antibodies
Buffer acid and alkaline substances in the blood to maintain
Acid-base balance function
optimal pH
Exert osmotic pressure to maintain optimal fluid balance in
Fluid balance function
body tissues, particularly the blood
Provide source of energy to the Krebs cycle when deaminated;
Energy function
excess protein may be converted to glucose or fat for
subsequent energy production
Provide movement when structural muscle proteins use energy
Movement function
to contract
1. Structural function
2.
3.
4.
5.
6.
7.
8.
9.
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D.
Vitamins
1. Control metabolic functions
2. Fat soluble vitamins—A, D, E, K
3. Water soluble vitamins—B complex vitamins and C
Roles of vitamins important to sports performance. A number of B vitamins, including thiamin,
riboflavin, niacin, B6, and pantothenic acid, are essential for the conversion of carbohydrate into energy
for muscular contraction. Vitamin B12 and folic acid are essential for the development of the red blood
cells (RBC), which deliver oxygen to the muscle cell. Vitamin E helps protect the RBC membrane from
destruction by free radicals. Vitamin E and other antioxidant vitamins are theorized to prevent free
radical damage in muscle cells during exercise. Vitamin C is needed for the formation of epinephrine
(adrenaline), a key hormone during strenuous exercise. Niacin may actually block the release of free
fatty acids from the adipose tissue, which could be a disadvantage for ultraendurance athletes. Finally,
several of the B vitamins are also involved in the formation of neurotransmitters in the brain, which may
induce a relaxation effect.
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E.
Minerals
1. Control metabolic functions
2. Give hardness to certain tissues
Minerals contribute to many functions in the body.
Function
Ion balance in cells
Cell metabolism
Bone health
Growth and development
Blood formation and clotting
Nerve impulses
Antioxidant defenses
F.
Minerals
Sodium, potassium, chloride
Calcium, phosphorus, magnesium
Calcium, phosphorus, fluoride, magnesium
Calcium, phosphorus, zinc
Iron, copper, calcium
Sodium, potassium, chloride, calcium
Selenium, zinc, copper, magnesium
Water
1. Control metabolic functions
2. Temperature regulation
3. Elimination of by-productions of metabolism
III.
True Foods—have potential for caloric value to release energy to produce ATP
A. Carbohydrates = 4 kcals per gram
B. Fats = 9 kcals per gram
C. Proteins = 4 kcals per gram
D. Primary energy releasing foods = CHO and fat
IV.
Proteins and Training
A. Protein requirements (USRDA)
1. USRDA = United States Recommended Dietary Allowance
a. A recommendation made for the amount of selected nutrients that a person should have
in the daily diet. The amount is well above the minimum requirements of the daily diet
2. Protein (USRDA) = .8 grams per kilogram of body weight
a. A person in strenuous athletic training may need 1.6 to 2.0 grams per kilogram of body
weight
B. Protein supplements
1. One pound of new muscle per week = 100 grams of protein per week or 14.3 grams per day
2. Recommended daily intake = .8 g/kg/day or about 56 grams per day. 56 + 14.3 = 70.3
grams per day. A recent survey indicated that the average daily protein intake = 105 grams.
Protein supplements to support muscle development in most cases are not needed.
184
C. Amino acid supplements
1. Known as free form and branched chain amino acids
2. Intake may cause an imbalance in the pool of amino acids available. Excess use of one
amino acid may decrease utilization of another
a. Example: Excess leucine may interfere with use of isolucine and valine
3. No research to support the use of excess amino acids
D. Comparison of protein supplements and natural foods
1. Three of the essential amino acids, leucine, isoleucine, and valine are often promoted in
supplements because they compose 35% of muscle protein
2.
Branched Chain
Peanut
Amino Acids
Supplement Egg Milk Beef Fish Beans Butter
E.
F.
Leucine
2016
2400
2700
3140
3200
2700
2400
Isoleucine
1193
2430
2400
2200
2150
2270
1517
Valine
1164
2700
2600
2270
2150
1600
1610
Totals
4373
7530
7700
7610
7500
6570
5527
Values are in milligrams for one serving
Procedure to follow to determine need for protein supplements
1. Determine daily caloric intake
2. Determine percentage that is protein (16% needed to increase LBM)
3. Determine amount of complete and incomplete protein
4. Decide if subject needs increased protein supplementation
5. If needed, consider using natural foods. Examples are egg whites and chocolate milk
Gaining body weight
1. Set a reasonable goal within a certain time period. The greatest gains will be made in the
first three months; in untrained young men, this gain can be approximately 3 pounds per
month. In well-trained athletes and women, the gains will be much less. Gender and
genetics are two of the major controlling factors in how much and how fast the lean body
mass will be gained. After a few years of dietary intervention and training, the gains are
reduced and may be about 1 to 3 percent increase per year
2. An individual on a weight-gain program should follow the same dietary principles
advocated for those who are maintaining or even trying to lose body weight. The only
major difference will be that greater amounts of foods will be consumed to gain weight
3. Increase your caloric intake. To add a pound of muscle tissue per week, you need to
increase your caloric intake by approximately 400 calories and you would need about 14
grams of additional protein per day. One glass of skim milk, 3 slices of whole wheat bread,
and 2 hard-boiled egg whites will provide the necessary calories and about 23 grams of
protein
Many people assume that protein is the important food for increasing muscle mass, but
total energy intake, primarily from carbohydrate, is what allows the body to train and to
bring about the increased gain in muscle size. A more specific guideline for the total amount
of protein needed is that an intake of 1.8 grams of protein per day for each 2.2 pounds of
body weight will adequately meet the needs of a weight gain program.
4. Start a strength-training exercise program. It is important to understand that it is not the
intake of food that provides the stimulus for increased muscle mass; rather, the use of the
overload principle in a strength-training program is what causes the muscle to increase in
size.
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5.
6.
V.
VI.
Use a tape measure to take body measurements. Be sure to take them at the same place
every 1 to 2 weeks. Body parts measured should include the neck, upper and lower arm,
chest, abdomen, thigh, and calf. This measuring is to ensure that body weight gains are
proportionately distributed. You should look for good gains in the chest and limbs, but the
abdominal girth increase should be kept low because that is where fat usually increases the
most. Remember, the weight gain should be in lean body mass, especially muscle, and not
in fat mass.
Be aware of the misleading information concerning dietary supplements that promise to
effectively increase the amount of lean muscle mass. Most advertised claims are
speculative, since very little well-controlled research has been conducted for most of these
purported nutritional supplements
Energy Available for Muscle Contraction
A.
Source
Supply—Kg/Muscle
Energy Kcals/Mole
Total Energy (Kcals)
ATP
PC
Glycogen
FFA (Fat)
4.0 mmoles
15.6 mmoles
15.0 gm
>10% of body weight
10
10.5
700
varies
0.8
3.3
1200
60,000
Energy Releasing Systems and How They Might Be Affected by Nutritional Intervention
A. ATP-PC system
1. (Stored) ATP —÷ ADP + Pi
2. (Stored) PCr —÷ Pi + Cr
8Substrate
B. Anaerobic glycolysis
C6H12O6 ————————÷ Anaerobic Glycolysis ——————÷ Lactic Acid
9
9
heat
buffered in plasma
• CHO overloading
• replenishment of H2O
• Increase the amount
• Decrease time to
of alkaline reserve
replenish CHO
(NaHCO3)
C. Aerobic Systems
CHO
—————————÷ Aerobic Systems ——÷ H2O + CO2
Fats ©
9
heat
• CHO overloading
• replenishment of H2O
• Decrease time to
replenish CHO
VII. Fatigue and Carbohydrate
A. Fatigue may be attributed to:
1. Decreased blood glucose = 3.3 mm or less
2. Decreased muscle glycogen = 50 mm per kg of wet muscle or less
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VIII. Ways Nutritional Intervention Might Affect Performance
A. Carbohydrate (glycogen) overloading
B. Carbohydrate (glycogen) replenishment
C. Water replenishment
D. Increase the alkaline reserve (NaHCO3)
E. Increase creatine to affect ATP-PC system
F. Pre-game meal
IX.
Carbohydrate (Glycogen) Overloading
A. Effect of diet on glycogen stores and endurance
1. Workload = 75% maximum aerobic capacity
2. Normal mixed diet (3 days)
a. Glycogen content = 1.75 grams per 100 grams of wet muscle
b. Maximum work time = 114 minutes
3. Fat and protein diet (100% fat and protein—3 days)
a. Glycogen content = 0.63 grams per 100 grams of wet muscle
b. Maximum work time = 57 minutes
4. High carbohydrate diet (about 80% CHO—3 days)
a. Glycogen content = 3.51 grams per 100 grams of wet muscle
b. Maximum work time = 167 minutes
B. Effect of carbohydrate loading as a function of distance
DISTANCE
LOADING EFFECT (SECONDS SAVED)
10 miles
36.0
15 miles
112.2
20 miles
211.2
26.2 miles
507.6
C. Carbohydrate loading procedure (recommended)
MON
TUE
WED
THU
FRI
SAT
Diet
Mixed
Mixed
High CHO (80%)
High CHO
High CHO
High CHO
Training Heavy
Heavy
Moderate
Light
Light
Event
Note:
Keep the daily caloric constant, just change the percentage of foods
D. One day carbohydrate overloading
1. Work bout before overloading = 5-minute warm-up, 150-second work at 130% VO2 peak,
30-second all-out sprint
2. Carbohydrate loading protocol
a. 10.3 grams of CHO per kg of body weight
b. 12 grams of CHO per kg of lean body mass
c. Start ingesting CHO within 20 minutes after the end of exercise
d. Glycogen increased from 109.1 ± 8.2 mmol per kg of wet muscle to 198.2 ± 13.1 mmol
per kg of wet muscle in 24 hours
3. One-Day Carbohydrate Overloading
a. Physical inactivity—day before contest
b. Ten (10) grams of CHO per kg of body weight
c. High glycemic index for foods and drinks
d. Increased glycogen stores by 90% after one day with no additional significant increase
after two more days of the diet and inactivity intervention.
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E.
F.
Carbohydrate (Glycogen) Replenishment
A. Effects of successive days of training on muscle glycogen content
EFFECTS OF SUCCESSIVE DAYS OF TRAINING ON
MUSCLE GLYCOGEN CONTENT
Blood flow to muscles is enhanced immediately
120
following exercise and muscle cells can pick up
more glucose and are more sensitive to the
High CHO Diet (70%)
100
effects of insulin, a hormone that promotes the
movement of glucose into the muscle cell and
80
the synthesis of glycogen
60
2. Ingestion of Protein—One study indicated that it
Low CHO Diet (40%)
could be helpful to ingest protein with the
40
carbohydrates. A ratio of one gram of protein
per three grams of carbohydrate might be
20
2 hr. Training Bouts
beneficial
0
3. Need about 3.9 grams of CHO per pound of
0
24
48
72
body weight over a 24-hour period
Hours
Studies have shown that consuming carbohydrates
within 15 minutes after exercise restores glycogen levels more rapidly. Glycogen replenishment was 45%
less in athletes who waited 2 hours before consuming carbohydrates
1.
Muscle Glycogen (mmol/kg wet wt.)
X.
Carbohydrate loading procedure (not recommended)
FAT
PROTEIN
EXERCISE
INTENSITY
DAY CHO
1
No
High
Normal
Specific to event
High
2
No
High
Normal
Specific to event
High
3
No
High
Normal
Major muscles in event
Exhaustive
4
High
High
Normal
Anaerobic nonspecific
Moderate
5
High
No
Normal
Anaerobic nonspecific
Moderate
6
High
No
Normal
Active rest
Light
7
High
No
No
Competition
1. Possible risks of non-recommended program
a. Increased production of ketone bodies (acidosis)
b. Increased secretion of nitrogen
c. Glucose deficiency in the depletion phase may cause fatigue, changes in mood,
irritability, slow thinking, lightheadedness, nausea, dizziness, and fainting
d. Sudden increases in CHO may trigger insulin reaction
e. Sudden increases in CHO might cause water retention
Effect of proper training and proper diet on muscle glycogen stores
B.
188
1.
2.
3.
XI.
Carbohydrate replenishment schedule
a. Consume approximately 50–100 grams of carbohydrate immediately after exercise
b. Consume another 50–100 grams of carbohydrate about 2 hours later
c. Then return to a regular, well balanced diet
Carbohydrate replenishment formula
a. 17 Tablespoons of sugar per quart of water = 200 g CHO
b. 8.5 Tablespoons of sugar per quart of water = 100 g CHO
c. Drink 1 pint immediately after exercise
d. Drink 1 pint within 2 hours after exercise
e. Use unsweetened Kool-Aid for flavor
A product that is relatively cheap and might affect protein synthesis is chocolate milk. One pint of
chocolate milk contains 260 calories, 16 grams of complete protein (this means it contains all of the
essential amino acids that can’t be produced by the body), 48 grams of carbohydrate, 4 grams of fat,
and 600 milligrams of calcium. Chocolate milk is preferred over white milk since the high glycemic
index of the carbohydrate may increase the absorption of the protein and carbohydrate.
Milk contains two unique kinds of protein, known as whey protein and casein protein. Whey
protein is absorbed quite rapidly and the casein protein is taken up more slowly. By using milk, the
body now has a product that will provide the muscle cells with an intake of amino acids for an
extended period of time.
It should be noted that milk contains lactose and one should be aware if they are unable to
tolerate lactose.
Comparison of Energy Bars and Other Sources
Size (oz)
Calories
Carbs (g)
Carbs (%)
Protein (g)
Fat (g)
Fat (%)
Price
PowerBar
Chocolate
2.25
225
42
75
10
2
8
$1.69
Gatorbar
Raspberry
1.17
110
25
90
1
1
8
$1.29
Clif Bar
Dark
Chocolate
2.4
250
52
83
5
2
7
$1.69
PR*Bar
Chocolate
Peanut
1.6
190
19
40
14
6
28
$2.50
Exceed
Sports Bar
Oatbran
2.8
280
53
76
12
2
6.5
$1.89
Nature Valley
Lowfat
Granola Bar
1
110
21
76
2
2
16
33 cents
A. Comparison
1. Four fig bars = 44 grams of CHO
2. One medium banana = 25 grams of CHO
3. One large egg = 6 grams of protein
XII. Consumption of Excessive Amounts of Carbohydrate During and Just Before Athletic Contests
A. Negative effects
1. Triggers a release of insulin which reduces the ability of muscle to utilize fat
189
INSULIN RESPONSE
Blood
Muscle Cell
C6H12O6
Insulin
2.
3.
4.
active transport
system
tes
a
iv
act
inactivates
Fat
Metabolism
Rapid intake of blood glucose into muscle tissue may cause mild hypoglycemia
Could reduce exercise time to exhaustion by 19%
Draws fluid in GI tract from other parts of the body and this contributes to dehydration
EFFECT OF SUGAR ON H2O
GI
Tract
Blood
Muscle
Cell
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
Sweating during exercise
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
C6H12O6
C6H12O6
B. Carbohydrate before exercise
1. Once exercise begins, insulin levels fall and blood glucose returns to normal.
Misunderstanding this process leads some people either to avoid carbohydrates or consume
nothing at all before exercising. In reality, eating pre-exercise carbohydrate with ample
water provides additional nutrients for activity. The best time to eat the carbohydrate for
shorter events is about 5 to 10 minutes before exercising. The critical point is to have
adequate carbohydrate replenishment the days preceding the event and to reduce the training
to assure ample glycogen stores
2. Workloads longer than 90 minutes
a. Four hours before event = 4–5 grams of CHO per kg of body weight
b. One hour before event = 1–2 grams of CHO per kg of body weight
(1) Fitness for Life
(a) One fruit exchange = 15 grams CHO
(b) One bread-starch exchange = 15 grams of CHO
c. Ten minutes before event = 50–60 grams of CHO in a 40–50 percent solution
(1) Formula:
(a) One level teaspoon = 5 grams
(b) 50 grams in a 50 percent solution = 10 level teaspoons in 100 milliliters
(about 3–4 ounces) of water
190
C. Carbohydrate during exercise
1. Prolonged strenuous exercise increases plasma concentrations of the hormones epinephrine,
growth hormone, cortisol, and glucagon. Insulin is decreased.
2. Ingestion of carbohydrate during prolonged exercise blunts these hormone responses and
delays fatigue.
3. The blunted hormone response may contribute to a delay in both central (brain) and
peripheral (muscle) fatigue by helping to spare liver and muscle glycogen, maintain blood
glucose, and reduce blood concentrations of free fatty acids, free tryptophan, and ammonia.
4. To prevent a fall in blood glucose concentration and to blunt the hormonal response to
exercise, every 15–20 min athletes should drink 8–12 oz (240–350 ml) of a sports drink that
contains carbohydrate.
5. Range = 2.5–10%. Best might be 6–8%
6. Increased performance might be due to the maintaining of the blood glucose levels at a time
when muscle glycogen stores are diminished
7. Replacement drink
a. One quart of water. Warm the water to aid in dissolving the sugar
(1) 4 Tablespoons of sugar = 5% solution
(2) 5 Tablespoons of sugar = 6.3% solution
(3) 6 Tablespoons of sugar = 7.6% solution
b. Add .5 teaspoon of salt per quart of water to aid in water absorption and to stimulate
the thirst mechanism
c. Use unsweetened Kool-Aid for flavor
d. Chill solution to about 40–50ºF to decrease the transit time through GI tract
D. Comparison of commercial replenishment beverages
Beverage
CHO Concentration (%)
CHO Source
Body Fuel 450
Quickick
Gatorade
10-K
Sqwicher
Exceed
Recharge
Coca-Cola
Orange juice
Cranberry juice
4.5
4.7
6.0
6.3
6.8
7.2
7.6
10.7
11.8
15.0
Glucose–Fructose
Fructose–Sucrose
Sucrose–Glucose
Sucrose–Glucose–Fructose
Glucose–Fructose
Glucose–Fructose
Fructose–Glucose
Corn Syrup–Sucrose
Fructose–Sucrose–Glucose
Corn Syrup–Sucrose
191
Some recommended guides for carbohydrate intake as a means to help optimize exercise/sport performance. Carbohydrate intake before
and during exercise may help optimize performance, whereas carbohydrate intake after exercise may facilitate recovery for subsequent
training for competition. In general, the lower the intensity and the shorter the duration of exercise, the less the need for additional
carbohydrate. Recommendations are based on scientific studies. Physically active individuals should consume various types and amounts of
carbohydrate before and during exercise and sport training to determine personal optimal dietary strategies.
Exercise intensity/sport
Duration
Before exercise*
During exercise**
After exercise***
Very high-intensity aerobic (5K run)
< 30 minutes
None needed
None needed
High-intensity aerobic (10K run)
30–90 minutes 20–25 grams
30–60 grams
60–90 minutes 20–25 grams
30–60 grams
Intermittent high-intensity
(Team sports, such as soccer)
Moderate- to high-intensity aerobic
(half-marathon; marathon)
> 90 minutes
Moderate-intensity aerobic
> 6 hours
Ironman-distance triathlon; 140 miles; 226
kilometers)
High-intensity resistance training (Lifting
weights)
1–2 hours
20–50 grams
Carbohydrate loading
20–50 grams
Carbohydrate loading
60–80 grams/
hour
60–100
grams/hour
None needed
None needed
None needed
60–80 grams/hour
for 3–4 hours
60-80 grams/hour
for 3–4 hours
60 grams/hour for
3–4 hours
60–80 grams/hour
for 3–4 hours
60–80 grams/hour
for 3–4 hours
*Within 10–15 minutes of the start of exercise. All individuals should consume a pregame meal sometime between 1–4 hours prior to exercise in order to
ensure normal muscle glycogen and blood glucose levels. Carbohydrate intake 3–4 hours before should average about 3–4 grams per kilogram body weight,
but only 1–2 grams per kilogram body weight if consumed within 1–2 hours exercise.
**Fluids such as sports drinks are recommended. Drinking about 8 ounces (240 milliliters) of a typical sport drink every 15 minutes will provide about 60
grams of carbohydrate per hour.
***For most athletes, consuming a diet with substantial amounts of healthful carbohydrates over the course of 24 hours will replace muscle glycogen levels to
normal. For those who want a speedy recovery of muscle glycogen for subsequent intense training or competition the same or following day, using this rapid
muscle glycogen replacement protocol may be recommended. Athletes may also benefit by consuming some protein with the carbohydrate, about 1 gram of
protein for every 4 grams of carbohydrate.
XIII. Fluid Replacement—proper hydration is important before exercise, during exercise, and after exercise
Effect of water loss on athletic performance
Water Loss as Percent of Body Weight
A.
1.
2.
8 .0 0
6 .0 0
>6%
4 .0 0
4-6%
2 .0 0
3%
0 .0 0
2%
Impaired
Athletic
Ability
Reduced
Muscle
Endurance
Reduced
Muscle
Strength
Heat Cramps
Heat Exhaustion
Effect of Water Loss on Athletic Performance
A loss of more than 2% of body weight, day by day, puts an individual in jeopardy of dehydration
Decreases in plasma volume (10–15%)
a. Increase exercise heart rate
b. Decrease stroke volume
c. Impair thermoregulation
d. Affects hydrolysis—any reaction in which water is one of the reactants
e. Decrease in work capability
192
3.
B.
Most athletes lose substantially more body fluids through sweat than they replace by drinking during
exercise. This so-called “voluntary dehydration” can have serious implications for health and
performance.
4. An athlete’s failure to drink sufficient fluids is caused by many factors, including the physiological
inhibition of thirst that occurs after moistening the mouth with a beverage, the uncomfortable
sensation of fluid in the stomach, poor access to beverages during exercise, poor quality of available
beverages, and a lack of education about the need to drink during exercise.
5. After becoming dehydrated, elderly individuals tend to drink less than their younger counterparts.
6. Athletes can be trained to become “better drinkers” before, during, and after exercise.
7. Improving the flavor of a beverage can dramatically increase the consumption of fluids during
exercise.
8. Although athletes will drink more of a cool beverage than a warm one, the temperature of the drink
has no important effect on core body temperature.
Recommendations for fluid replacement
1. Before exercise (2 hours prior)
a. Drink 500 ml (17 oz)
2. During exercise
a. Drink 600–1200 ml (20 to 40 oz) per hour
b. Drink 150–300 ml (6–10 oz) every 15–20 minutes
3. After exercise
a. Based on pre- and post-body weight
b. Drink 50% over and above the volume needed to restore pre-exercise body weight. This
compensates for urine losses, which may induce hypohydration when only 100% of fluid is
consumed based on weight loss
C. Negative effects of decreases in plasma volume (10–15%)
1. Increase in exercise heart rate
2. Decreased stroke volume
3. Impaired thermoregulation
4. Affects hydrolysis—any reaction in which water is one of the reactants
5. Decreased work capacity
D. Sample heat acclimatization schedule for football and other sports
1.
Tips for Safer Two-A-Days
Injury rates increase during two-a-day workouts whether athletes are in peak physical condition or
not. In fact, many athletes don’t even make starting lineup because of injuries incurred during
preseason training.
Here are some tips to help ensure athletes stay at their best and prevent heat-related injuries
during two-a-days.
Encourage Athletes to Begin Conditioning Before Two-A-Days
Encourage athletes to begin conditioning in the heat two weeks before official practice
begins. This allows athletes’ bodies to cool more efficiently by increasing sweat production
sooner than when they are not acclimated to the heat.
Avoid Workouts During Unusually Hot Temperatures
Practice sessions during unusually hot and humid conditions should be limited to very
moderate workouts, postponed until cooler times of the day or brought inside to avoid the
heat.
193
Make Fluids Part of the Playbook
Before, during and after competition, be
sure to consume adequate amounts of
fluid. Athletes can make sure they are
properly hydrated by checking their
urine color: lighter urine color indicates
athletes are better hydrated. The longer
the workout session, the more frequently
fluids need to be replaced. Research
shows that a sports drink containing a
6% carbohydrate solution, like Gatorade,
can be absorbed as rapidly as water. But
unlike water, a sports drink can provide
energy, delay fatigue and improve
performance.
Signs of Dehydration and Heat Illness
Dehydration can seriously compromise athletic
performance and increase the risk of exertional
heat injury. That’s why it’s important to recognize
the warning signs.
þ Thirst
þ Dizziness
þ Irritability
þ Cramps
þ Headache
þ Nausea
þ Weakness
þ Decreased performance
Use the Shade
Before practice, warm up in the shade and be sure to rest in the shade during breaks. Even
during rest, exposure to heat can raise the body temperature, increase fluid loss and decrease
the blood available to the muscles during workouts.
Recommend Wearing Loose Fitting Clothing
Cotton blend, loose fitting clothing can help promote heat loss. The rule: the less clothing,
the better.
Be Prepared for an Emergency
Always have a cell phone on hand and be familiar with emergency numbers. Also keep ice
and ice towels on hand in case of heat-related emergencies.
2.
Fluid Guidelines for Two-A-Days
Proper hydration is the best safeguard against heat illness. Remember to have athletes drink
before, during and after training and competition.
Before Exercise
T
T
2 to 3 hours before exercise drink at least 17 to 20 oz of water or a sports drink.
10 to 20 minutes before exercise drink another 7 to 10 oz of water or a sports drink.
What to Drink During Exercise
Drink early—Even minimal dehydration compromises performance. In general, every 10 to
20 minutes drink at least 7 to 10 oz of water or a sports drink. To maintain hydration,
remember to drink beyond thirst. Optimally, drink fluids based on amount of sweat and
urine loss.
T Athletes benefit in many situations from drinking a sports drink containing
carbohydrate.
194
T
T
T
T
T
If exercise lasts more than 45 to 50 minutes or is intense, a sports drink should be
provided during the session.
The carbohydrate concentration in the ideal fluid replacement solution should be in the
range of 6% to 8% (14 to 18 g/8 oz).
During events when a high rate of fluid intake is necessary to sustain hydration, sports
drinks with less than 7% carbohydrate should be used to optimize delivery.
Fluids with salt (sodium chloride) are beneficial to increasing thirst and voluntary fluid
intake as well as offsetting the amount in lost sweat.
Cool beverages at temperatures of 50° to 59° F are recommended.
What Not to Drink During Exercise
T
T
Fruit juices, carbohydrate gels, sodas and those sports drinks that have carbohydrate
levels greater than 8% are not recommended as the sole beverage.
Beverages containing caffeine, alcohol and carbonation are discouraged during exercise
because they can dehydrate the body by stimulating excess urine production, or
decrease voluntary fluid intake.
After Exercise
Immediately after training or competition is the key time to replace fluids. Weigh athletes
before and after exercise. Research indicates that for every pound of weight lost, athletes
should drink at least 20 oz of fluid to optimize rehydration. Sports beverages are an
excellent choice.
3.
Managing Two-A-Days
Stay Cool
T Get in shape and acclimate
T Know the warning signs of dehydration and heat illness
T Don’t rely on thirst to drink
T Drink on schedule
T Favor sports drinks
T Monitor body weight
T Watch urine color and caffeine intake
T Key in on meals as an opportunity to increase fluid intake
T Stay cool when you can
From: Eichner, E.R. (1998). Treatment of Suspected Heat Illness. Int. J. Sports Med
19:S150-153.
Stay Healthy
T
T
T
T
T
T
T
Minimize the stresses of life
Eat a well-balanced diet
Avoid overtraining
Sleep well
Avoid rapid weight loss
Avoid people with colds
Keep hands away from nose and mouth
195
T Get a flu shot
T Stay hydrated and ingest carbohydrates during exercise
From: Niemen, D.C. (1998). Immunity in Athletes: Current Issues. Sports Science Exchange
11(2): 1-6.
Stay Hydrated
T
T
T
T
T
T
Drink throughout the day
Drink at least 17 to 20 oz of fluid 2 to 3 hours before a practice or game
Drink an additional 7 to 10 oz of fluid 10 to 20 minutes competition
Drink 28 to 40 oz of fluid per hour of play (at least 7 to 10 oz every 10 to 15 minutes)
to replace sweat loss during exercise
Drink at least 20 oz per pound of weight loss within two hours of finishing training or
competition
Optimal to have fluid intake match sweat and urine loss.
From: Casa, D. et al. Journal of Athletic Training 35(2): 212-224, 2000.
Requirement
Day 1
Day 2
Day 3
Day 4
Day 5
Time—minutes
60
80
100
120
120
Uniform
shorts
shorts
pants
pants-helmet
full gear
Workout
calisthenics
and jogging
calisthenics
and sprints
drills and
sprints
drills and
sprints
full
practice
Frequent breaks and fluid replacement highly recommended
E.
Field tests for adequate water intake
1. Clear urine
2. Relatively large volume of urine
3. Urine doesn’t smell
XIV. Increasing the amount of sodium bicarbonate (NaHCO3) available to buffer lactic acid
A. Gains in performance for tasks of high intensity that last from one to ten minutes or involve
repeated bouts of high intensity exercise with short recovery periods could benefit from an
increase in buffering capacity
B. Effective dosage = 0.3 grams of sodium bicarbonate (baking soda) per kilogram of body weight
taken over a 2-hour period with the performance taking place 2.5 hours after the start of
ingestion. Place 1.5 grams of sodium bicarbonate in each capsule. Also ingest at least one liter
of water during the time period. Example: A 70 kg person would ingest 14 capsules containing
1.5 grams of sodium bicarbonate over a 2-hour period. A capsule would be ingested about every
8.5 minutes
C. Possible negative side effects
1. Large doses of sodium bicarbonate can cause diarrhea and vomiting
2. Be sure to experiment during practice to determine if an individual can tolerate the sodium
bicarbonate
196
XV. Overloading of Creatine (ATP-PC System)
A. Read article on creatine in appendix at the end of this unit, p. 225
B. Creatine
energy to do work
ATP
ADP + Pi
ATP
ADP + Pi
coupled reaction
PCr
Pi + Cr
1. An amino acid found primarily in meat and fish
2. Average daily intake = about 1 gram
3. Daily requirement = about 2 grams
4. Synthesized in the liver, kidneys, and pancreas from the amino acids arginine and glycine
C. Possible benefits
1. Strength training and repeated bouts of high intensity intermittent work
a. Increased creatine might allow the athlete to sustain high intensity workouts for longer
periods which could provide a greater training and enhanced physiological adaptation over
time
b. Might help in allowing a faster recovery between work bouts
D. Creatine and carbohydrate
1. Combining creatine supplementation with carbohydrate may augment creatine accumulation
in the muscle cell and it may increase the storage of glycogen
2. This could be helpful for sports such as hockey, soccer, basketball, and wrestling
E. Possible negative side effects
1. No long term research to determine side effects
2. Subjective observations indicate water retention and athlete may be susceptible to muscle
cramps, pulls, and spasms
3. Make sure the athlete is always well hydrated when taking creatine supplements
F. Creatine dosage (creatine monohydrate)
1. To elevate creatine stores = 20 grams per day for 5 days; .3 grams/kg/day for five days
2. To maintain elevated creatine stores = 3 grams per day; .03 grams/kg/day
XVI. Pre-Event and Pre-Game Nutrition
A. Read article on pre-game meal in appendix at the end of this unit, p. 237
B. Questions to ask subject
1. What is the activity you are training for?
2. What are the outcomes you want?
C. Pre-Event Meals
1. Determine total calories and percentages for a balance diet using Fitness for Life and
ChooseMyPlate.gov materials
2. Explain how to manipulate training and dietary intake to have an effect on replacement of
nutrients, such as fluids, glycogen, protein, and creatine
D. Pre-Game Meal
1. The main purpose of the pre-game meal is to provide the athlete with adequate carbohydrate
and assist in providing optimal hydration
2. When the athlete has a competition scheduled after going without food during the night, the
effect on liver glycogen becomes important. Liver glycogen is the primary endogenous
197
source of carbohydrate to maintain a proper blood glucose level
As a result of this reasoning, it is suggested that approximately 50–100 grams of
carbohydrate should be included in the pre-game meal with only enough fat and protein to
aid in off-setting hunger pangs
It should be emphasized that the eating schedule during the days previous to the event are much
more important than the composition of the pre-game meal
3.
E.
BODY COMPOSITION PROGRAMS
I.
In a one-month survey of newspapers and magazines, the FDA found 435 questionable ads, over half
of which were for weight-loss products
A. Read articles in appendix at end of this unit
1. Diet Plans: Rationale and Reality, p. 238
2. Over-the-Counter Diet Aids: Rationale and Reality, p. 239
II.
Fat Cells—the results of research suggest that:
A. The number of fat cells in the human body is established during periods of rapid growth
1. The latter part of gestation
2. The first year of infancy
3. Adolescence
B. Once established, the number of fat cells is fixed
C. Non-obese adults have about 27 billion fat cells while the obese adults have 42 to 106 billion fat
cells
D. Fat cell size is liable and varies with weight gain or loss
E. Comparing obese and non-obese adults, cell size is only some 40% greater, while the cell
number is about 190% higher in the obese
III.
Obesity (20%+ in males and 30%+ in females)
A. 14% of obese infants become obese adults
B. 40% of obese children (7 years) become obese adults
C. 70% of obese children (10–14 years) become obese adults
CREEPING OBESITY
High
Low
Activity
25
Diet
BMR
35
45
Fatness
55
Age
D. Longevity
1. Females in the U.S. = 79.3 years
2. Females in Okinawa = 82.5 years
a. Diet—(73- to 88-year-old women) = 1360 calories per day
b. 56% carbohydrate, 28% fat, 18% protein
198
E.
IV.
Patterns of obesity
1. Abdominal pattern obesity (apples)
a. Excessive accumulation of fat that is concentrated above the waist, in the nape of the
neck, shoulders, and abdomen
2. Gluteal femoral obesity (pears)
a. Excessive accumulation of fat that is concentrated in the area of the buttocks and thighs
Factors That Cause a Decrease in Body Fat
A. Dietary intervention to manipulate caloric intake
B. Aerobic exercise to increase caloric output by using stored fat
C. Strength program to increase lean body mass and thus increase resting metabolic rate
D. Balanced diet
1. Carbohydrate = 5–6 grams per kg of body weight
2. Fat = 1 gram per kg of body weight
3. Protein = .8–1.5 grams per kg of body weight
4. Percentage of total calories
a. CHO = 60%
b. Fat = 25%
c. Protein = 15%
5. To maintain body weight = 15 kcals per pound
a. 1 gram CHO = 4 kcals
b. 1 gram fat = 9 kcals
c. 1 gram protein = 4 kcals
d. 1 gram = .035 ounces
6. Example
a. 150–lb person = 15 x 150 = 2250 kcals per day
b. CHO = 1350 kcals ÷ 4 = 337.5 grams x .035 = 11.81 ounces
c. Fat = 562.5 kcals ÷ 9 = 62.5 grams x .035 = 2.19 ounces
d. Protein = 337.5 kcals ÷ 4 = 84.38 grams x .035 = 3.0 ounces
7. Research at the City University of New York revealed that 20% of Americans’ calories
come from the following high-carbohydrate foods: cakes, cookies, pies, pastries, ice cream,
pudding, sugar, candy, syrup, soda pop, non-carbonated beverages, corn chips, tortilla chips,
and potato chips.
8. Food Exchange Program—Fitness for Life
a. Average American Diet
(1) 43%
Fat—high in saturated fat
(2) 45%
Carbohydrate—high in simple sugars
(3) 12%
Protein
b. Food Exchange Program
(1) 25%
Fat
(2) 60%
Carbohydrate—high in complex carbohydrates
(3) 15%
Protein
E. Food labels
1. Food labels contain nutrient information that can be valuable in the planning of a balanced
diet
199
Aerobic exercise to increase caloric output by using stored fat
1. Fat metabolism
a. 50% of fatty acids removed each cycle of circulation
b. Increased blood flow during aerobic exercise = increased total amount of fat removed
c. Increased size and number of mitochondria as a result of aerobic training increases the
ability to metabolize fat
d. Increased oxygen transport due to an increase in hemoglobin and total blood volume
brought about by an aerobic exercise program allows more oxygen to be available to
metabolize stored body fat
e. It takes time to turn on fat metabolism and thus the aerobic exercise should be 20
minutes or more in duration
% Fat/CHO in Exercise Metabolism
F.
100
Shift From CHO Metabolism Toward Fat Metabolism
During Prolonged Exercise
% Fat
80
60
40
% CHO
20
0
10
30
50
Exercise Time (min)
70
90
200
G. Strength training and control of body fat
1. Resting metabolic rate (RMR) = the amount of energy utilized during rest
a. Fat tissue v. muscle tissue = it requires 3 times more energy at rest to maintain a pound
of muscle tissue than the energy needed to maintain a pound of fat tissue
b. Strength training ÷ 8LBM ÷ 8RMR = 8use of stored fat at rest
(1) Increase of three pounds of muscle = increase of 40 kcals per day
(2) Increase of three pounds of muscle = expenditure of about four pounds of fat per
year
201
APPENDIX
1. Nutrition and Athletic Performance
2. Creatine Controversy
3. Creatine Supplementation and
Performance
4. Pregame Meal: To Eat or Not to
Eat—And What?
5. Diet Plans: Rationale and Reality
6. Over-the-Counter Diet Aids: Rationale
and Reality
202
Nutrition and Athletic
Performance
AMERICAN DIETETIC ASSOCIATION
DIETITIANS OF CANADA
JOINT POSITION STATEMENT
ABSTRACT
the United States, should provide individualized nutrition direction and advice
after a comprehensive nutrition assessment.
It is the position of the American Dietetic Association, Dietitians of Canada,
and the American College of Sports Medicine that physical activity, athletic
performance, and recovery from exercise are enhanced by optimal nutrition.
These organizations recommend appropriate selection of foods and fluids,
timing of intake, and supplement choices for optimal health and exercise
performance. This updated position paper couples a rigorous, systematic,
evidence-based analysis of nutrition and performance-specific literature with
current scientific data related to energy needs, assessment of body
composition, strategies for weight change, nutrient and fluid needs, special
nutrient needs during training and competition, the use of supplements and
ergogenic aids, nutrition recommendations for vegetarian athletes, and the
roles and responsibilities of the sports dietitian. Energy and macronutrient
needs, especially carbohydrate and protein, must be met during times of high
physical activity to maintain body weight, replenish glycogen stores, and
provide adequate protein to build and repair tissue. Fat intake should be
sufficient to provide the essential fatty acids and fat-soluble vitamins and to
contribute energy for weight maintenance. Although exercise performance
can be affected by body weight and composition, these physical measures
should not be a criterion for sports performance and daily weigh-ins are
discouraged. Adequate food and fluid should be consumed before, during,
and after exercise to help maintain blood glucose concentration during
exercise, maximize exercise performance, and improve recovery time. Athletes
should be well hydrated before exercise and drink enough fluid during and
after exercise to balance fluid losses. Sports beverages containing carbohydrates and electrolytes may be consumed before, during, and after exercise to
help maintain blood glucose concentration, provide fuel for muscles, and
decrease risk of dehydration and hyponatremia. Vitamin and mineral supplements are not needed if adequate energy to maintain body weight is consumed
from a variety of foods. However, athletes who restrict energy intake, use
severe weight-loss practices, eliminate one or more food groups from their
diet, or consume unbalanced diets with low micronutrient density may require
supplements. Because regulations specific to nutritional ergogenic aids are
poorly enforced, they should be used with caution and only after careful
product evaluation for safety, efficacy, potency, and legality. A qualified sports
dietitian and, in particular, the Board Certified Specialist in Sports Dietetics in
POSITION STATEMENT
This joint position statement is authored by the American Dietetic
Association (ADA), Dietitians of Canada (DC), and American College of
Sports Medicine (ACSM). The content appears in ADA style. This paper is
being published concurrently in Medicine & Science in Sports & ExerciseÒ
and in the Journal of the American Dietetic Association, and the Canadian
Journal of Dietetic Practice and Research. Individual name recognition is
reflected in the acknowledgments at the end of the statement.
KEY POINTS
0195-9131/09/4103-0709/0
MEDICINE & SCIENCE IN SPORTS & EXERCISEÒ
Copyright Ó 2009 by the American College of Sports Medicine, American
Dietetic Association, and Dietitians of Canada.
The following key points summarize the current energy,
nutrient, and fluid recommendations for active adults and
competitive athletes. These general recommendations can
be adjusted by sports nutrition experts to accommodate the
DOI: 10.1249/MSS.0b013e318190eb86
709
Copyright @ 2009 by the American College of Sports Medicine. Unauthorized reproduction of this article is prohibited.
SPECIAL COMMUNICATIONS
It is the position of the American Dietetic Association,
Dietitians of Canada, and the American College of Sports
Medicine that physical activity, athletic performance, and
recovery from exercise are enhanced by optimal nutrition.
These organizations recommend appropriate selection of
food and fluids, timing of intake, and supplement choices
for optimal health and exercise performance.
This ADA position paper uses ADA’s Evidence Analysis
Process and information from the ADA Evidence Analysis
Library (EAL). Similar information is also available from
DC’s Practice-based Evidence in Nutrition (PEN). The use
of an evidence-based approach provides important added
benefits to earlier review methods. The major advantage of
the approach is the more rigorous standardization of review
criteria, which minimizes the likelihood of reviewer bias
and increases the ease with which disparate articles may be
compared. For a detailed description of the methods used in
the evidence analysis process, access the ADA’s Evidence
Analysis Process at http://adaeal.com/eaprocess/.
Conclusion Statements are assigned a grade by an expert
work group based on the systematic analysis and evaluation
of the supporting research evidence: grade I = good, grade
II = fair, grade III = limited, grade IV = expert opinion only,
and grade V = a grade is not assignable because there is no
evidence to support or refute the conclusion.
Evidence-based information for this and other topics
can be found at www.adaevidencelibrary.com and www.
dieteticsatwork.com/pen and subscriptions for non-ADA
members are purchasable at https://www.adaevidencelibrary.
com/store.cfm. Subscriptions for DC and non-DC members
are available for PEN at http://www.dieteticsatwork.com/
pen_order.asp
203
SPECIAL COMMUNICATIONS
unique concerns of individual athletes regarding health,
sports, nutrient needs, food preferences, and body weight
and body composition goals.
Athletes need to consume adequate energy during
periods of high-intensity and/or long-duration training
to maintain body weight and health and maximize
training effects. Low energy intakes can result in loss
of muscle mass; menstrual dysfunction; loss of or failure
to gain bone density; an increased risk of fatigue, injury,
and illness; and a prolonged recovery process.
Body weight and composition should not be used as
the sole criterion for participation in sports; daily
weigh-ins are discouraged. Optimal body fat levels
depend on the sex, age, and heredity of the athlete and
may be sport-specific. Body fat assessment techniques
have inherent variability and limitations. Preferably,
weight loss (fat loss) should take place during the offseason or begin before the competitive season and
involve a qualified sports dietitian.
Carbohydrate recommendations for athletes range from
6 to 10 gIkgj1 body weightIdj1 (2.7–4.5 gIlbj1 body
weightIdj1). Carbohydrates maintain blood glucose
levels during exercise and replace muscle glycogen.
The amount required depends on the athlete’s total
daily energy expenditure, type of sport, sex, and environmental conditions.
Protein recommendations for endurance and strengthtrained athletes range from 1.2 to 1.7 gIkgj1 body
weightIdj1 (0.5–0.8 gIlbj1 body weightIdj1). These
recommended protein intakes can generally be met
through diet alone, without the use of protein or amino
acid supplements. Energy intake sufficient to maintain
body weight is necessary for optimal protein use and
performance.
Fat intake should range from 20% to 35% of total
energy intake. Consuming e20% of energy from fat
does not benefit performance. Fat, which is a source of
energy, fat-soluble vitamins, and essential fatty acids,
is important in the diets of athletes. High-fat diets are
not recommended for athletes.
Athletes who restrict energy intake or use severe
weight-loss practices, eliminate one or more food
groups from their diet, or consume high- or lowcarbohydrate diets of low micronutrient density
are at greatest risk of micronutrient deficiencies.
Athletes should consume diets that provide at least
the recommended dietary allowance (RDA) for all
micronutrients.
Dehydration (water deficit in excess of 2–3% body
mass) decreases exercise performance; thus, adequate
fluid intake before, during, and after exercise is
important for health and optimal performance. The
goal of drinking is to prevent dehydration from
occurring during exercise and individuals should not
drink in excess of sweating rate. After exercise,
710
Official Journal of the American College of Sports Medicine
approximately 16–24 oz (450–675 mL) of fluid for
every pound (0.5 kg) of body weight lost during
exercise.
Before exercise, a meal or snack should provide
sufficient fluid to maintain hydration, be relatively
low in fat and fiber to facilitate gastric emptying and
minimize gastrointestinal distress, be relatively high
in carbohydrate to maximize maintenance of blood
glucose, be moderate in protein, be composed of
familiar foods, and be well tolerated by the athlete.
During exercise, primary goals for nutrient consumption are to replace fluid losses and provide carbohydrates (approximately 30–60 gIhj1) for maintenance of
blood glucose levels. These nutrition guidelines are
especially important for endurance events lasting
longer than an hour when the athlete has not consumed
adequate food or fluid before exercise or when the
athlete is exercising in an extreme environment (heat,
cold, or high altitude).
After exercise, dietary goals are to provide adequate
fluids, electrolytes, energy, and carbohydrates to replace muscle glycogen and ensure rapid recovery. A
carbohydrate intake of approximately 1.0–1.5 gIkgj1
body weight (0.5–0.7 gIlbj1) during the first 30 min
and again every 2 h for 4–6 h will be adequate to replace glycogen stores. Protein consumed after exercise
will provide amino acids for building and repair of
muscle tissue.
In general, no vitamin and mineral supplements are
required if an athlete is consuming adequate energy
from a variety of foods to maintain body weight.
Supplementation recommendations unrelated to exercise, such as folic acid for women of childbearing
potential, should be followed. A multivitamin/mineral
supplement may be appropriate if an athlete is dieting,
habitually eliminating foods or food groups, is ill or
recovering from injury, or has a specific micronutrient
deficiency. Single-nutrient supplements may be appropriate for a specific medical or nutritional reason (e.g.,
iron supplements to correct iron deficiency anemia).
Athletes should be counseled regarding the appropriate
use of ergogenic aids. Such products should only be
used after careful evaluation for safety, efficacy,
potency, and legality.
Vegetarian athletes may be at risk for low intakes of
energy, protein, fat, and key micronutrients such as
iron, calcium, vitamin D, riboflavin, zinc, and vitamin
B12. Consultation with a sports dietitian is recommended to avoid these nutrition problems.
EVIDENCE-BASED ANALYSIS
Studies used in the development of this position paper
were identified from the PubMed database maintained by
the National Library of Medicine and CENTRAL database,
http://www.acsm-msse.org
Copyright @ 2009 by the American College of Sports Medicine. Unauthorized reproduction of this article is prohibited.
204
as well as through research articles and literature reviews.
Five topic-specific questions were identified for evidencebased analysis (Fig. 1) and incorporated into this position,
updating the prior position on nutrition and performance
(1). Search terms used were athlete, performance, power,
strength, endurance, or competition and macronutrient,
meal, carbohydrate, fat, protein, or energy. For the purpose
of this analysis, inclusion criteria were adults aged 18–
40 yr; all sport settings; and trained athletes, athletes in
training, or individuals regularly exercising. Because the
grading system used provides allowances for consideration
of study design, the evidence-based analysis was not limited
to randomized controlled trials. Study design preferences
were randomized controlled trials or clinical controlled
studies; large nonrandomized observational studies; and
cohort, case–control studies. All sample sizes were included
and study dropout rate could not exceed 20%. The
publication range for the evidence-based analysis spanned
1995–2006. If an author was included in more than one
review article or primary research articles that were similar
in content, the most recent paper was accepted, and earlier
versions were rejected. However, when an author was
included in more than one review article or primary
research article for which content differed, then both
reviews could be accepted for analysis.
The following exclusion criteria were applied to all
identified studies:
Adults older than 40 yr, adults younger than 18 yr,
infants, children, and adolescents
Settings not related to sports
Nonathletes
Critical illness and other diseases and conditions
Drop out rates 920%
NUTRITION AND ATHLETIC PERFORMANCE
Conclusion statements were formulated summarizing the
strength of evidence with respect to each question (Fig. 1).
The strength of the evidence was graded using the
following elements: quality, consistency across studies,
quantity, and generalizability. A more detailed description
of the methodology used for this evidence-based analysis
may be found on the American Dietetic Association’s Web
site at www.eatright.org/cps/rde/xchg/ada/hs.xsl/
8099_ENU_HTML.htm.
ENERGY METABOLISM
Energy expenditure must equal energy intake to achieve
energy balance. The energy systems used during exercise
for muscular work include the phosphagen and glycolytic
(both anaerobic) and the oxidative (aerobic) pathways. The
phosphagen system is used for events lasting no longer than
a few seconds and of high intensity. Adenosine triphosphate
(ATP) and creatine phosphate provide the readily available
energy present within the muscle. The amount of ATP
present in the skeletal muscles (È5 mmolIkgj1 wet weight)
is not sufficient to provide a continuous supply of energy,
especially at high exercise intensities. Creatine phosphate is
an ATP reserve in muscle that can be readily converted to
sustain activity for È3–5 min (2). The amount of creatine
phosphate available in skeletal muscle is approximately four
times greater than ATP and, therefore, is the primary fuel
used for high-intensity, short-duration activities such as the
clean and jerk in weight lifting or the fast break in
basketball.
The anaerobic glycolytic pathway uses muscle glycogen
and glucose that are rapidly metabolized anaerobically
through the glycolytic cascade. This pathway supports
events lasting 60–180 s. Approximately 25%–35% of total
muscle glycogen stores are used during a single 30-s sprint
or resistance exercise bout. Neither the phosphagen nor the
glycolytic pathway can sustain the rapid provision of
energy to allow muscles to contract at a very high rate for
events lasting greater than È2–3 min.
The oxidative pathway fuels events lasting longer than
2–3 min. The major substrates include muscle and liver
glycogen, intramuscular, blood, and adipose tissue triglycerides and negligible amounts of amino acids from muscle,
blood, liver, and the gut. Examples of events for which the
major fuel pathway is the oxidative pathway include a 1500m run, marathon, half-marathon, and endurance cycling or
Q1500-m swimming events. As oxygen becomes more
available to the working muscle, the body uses more of the
aerobic (oxidative) pathways and less of the anaerobic
(phosphagen and glycolytic) pathways. Only the aerobic
pathway can produce much ATP over time via the Krebs
cycle and the electron transport system. The greater
Medicine & Science in Sports & Exercised
Copyright @ 2009 by the American College of Sports Medicine. Unauthorized reproduction of this article is prohibited.
711
SPECIAL COMMUNICATIONS
FIGURE 1—Specific topics and the respective questions used for the
evidence analysis sections of the nutrition and athletic performance
project.
Publication before 1995
Studies by same author, which were similar in content
Articles not in English
205
dependence on aerobic pathways does not occur abruptly,
nor is one pathway ever relied on exclusively. The intensity,
duration, frequency, type of activity, sex, and fitness level of
the individual, as well as prior nutrient intake and energy
stores, determine when the crossover from primarily aerobic
to anaerobic pathways occurs (2).
Conversion of energy sources over time. Approximately 50%–60% of energy during 1–4 h of continuous
exercise at 70% of maximal oxygen capacity is derived
from carbohydrates and the rest from free fatty acid
oxidation (3). A greater proportion of energy comes from
oxidation of free fatty acids, primarily those from muscle
triglycerides as the intensity of the exercise decreases (3).
Training does not alter the total amount of energy expended
but rather the proportion of energy derived from carbohydrates and fat (3). As a result of aerobic training,
the energy derived from fat increases and from carbohydrates decreases. A trained individual uses a greater
percentage of fat than an untrained person does at the same
workload (2). Long-chain fatty aids derived from stored
muscle triglycerides are the preferred fuel for aerobic
exercise for individuals involved in mild- to moderateintensity exercise (4).
SPECIAL COMMUNICATIONS
ENERGY REQUIREMENTS
Meeting energy needs is a nutrition priority for athletes.
Optimum athletic performance is promoted by adequate
energy intake. This section will provide information
necessary to determine energy balance for an individual.
Energy balance occurs when energy intake (the sum of
energy from foods, fluids, and supplement products) equals
energy expenditure or the sum of energy expended as basal
metabolic rate (BMR), the thermic effect of food, the
thermic effect of activity (TEA), which is the energy
expended in planned physical activity, and nonexercise
activity thermogenesis (5). Spontaneous physical activity is
also included in the TEA.
Athletes need to consume enough energy to maintain
appropriate weight and body composition while training for
a sport (6). Although usual energy intakes for many intensely training female athletes might match those of male
athletes per kilogram body weight, some female athletes
may consume less energy than they expend. Low energy
intake (e.g., G1800–2000 kcalIdj1) for female athletes is a
major nutritional concern because a persistent state of
negative energy balance can lead to weight loss and
disruption of endocrine function (7–10).
Inadequate energy intake relative to energy expenditure
compromises performance and negates the benefits of
training. With limited energy intake, fat and lean tissue
will be used for fuel by the body. Loss of lean tissue mass
results in the loss of strength and endurance, as well as
compromised immune, endocrine, and musculoskeletal
function (11). In addition, long-term low energy intake
results in poor nutrient intake, particularly of the micro-
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Official Journal of the American College of Sports Medicine
nutrients, and may result in metabolic dysfunctions associated with nutrient deficiencies as well as lowered resting
metabolic rate (RMR). The newer concept of energy
availability, defined as dietary intake minus exercise energy
expenditure normalized to fat-free mass (FFM), is the
amount of energy available to the body to perform all other
functions after exercise training expenditure is subtracted.
Many researchers have suggested that 30 kcalIkg j1
FFMIdj1 might be the lower threshold of energy availability for females (12–15).
Estimation of energy needs of athletes and active individuals can be done using a variety of methods. The Dietary
Reference Intakes (DRI) (15,17) and the Dietary Guidelines
2005 (16) (http://www.health.gov/dietaryguidelines/
dga2005/report/HTML/D3_Disccalories.htm) provide energy recommendations for men and women who are slightly
to very active, which are based on predictive equations
developed using the doubly labeled water technique
that can also be used to estimate energy needs of athletes
(Fig. 2).
Energy expenditure for different types of exercise is
dependent on the duration, frequency, and intensity of the
exercise, the sex of the athlete, and prior nutritional status.
Heredity, age, body size, and FFM also influence energy
expenditure. The more energy used in activity, the more
calories needed to achieve energy balance.
Typical laboratory facilities are usually not equipped to
determine total energy expenditure. Therefore, predictive
equations are often used to estimate BMR or RMR. The two
prediction equations considered to most closely estimate
energy expenditure are the Cunningham equation (1980)
(18) and the Harris–Benedict equation (19). Because the
Cunningham equation requires that lean body mass be
known, sports dietitians typically use the Harris–Benedict
equation. To estimate total energy expenditure, BMR or
RMR is then multiplied by the appropriate activity factor of
1.8–2.3 (representing moderate to very heavy physical activity levels, respectively). Numeric guidelines such as these
(8) only provide an approximation of the average energy
needs of an individual athlete. An alternative method
for estimating exercise energy expenditure is to use metabolic equivalents (METs) recorded during a 24-h period
(20). Any of these methods can be used to estimate energy expenditure for the determination of energy intake
requirements and provide the sports dietitian with a basis to
guide the athletes or active individuals in meeting their
energy needs.
BODY COMPOSITION
Body composition and body weight are two of the many
factors that contribute to optimal exercise performance.
Taken together, these two factors may affect an athlete’s
potential for success for a given sport. Body weight can
influence an athlete’s speed, endurance, and power, whereas
body composition can affect an athlete’s strength, agility,
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206
FIGURE 2—The Dietary Reference Intake (DRI) method for estimating energy requirement for adults (17).
NUTRITION AND ATHLETIC PERFORMANCE
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SPECIAL COMMUNICATIONS
and appearance. A lean body, i.e., one with greater muscle/
fat ratio, is often advantageous in sports where speed is
involved.
Athletic performance cannot be accurately predicted
based solely on body weight and composition given that
many factors affect body composition (21). Some sports
dictate that athletes make changes in body weight and
composition that may not be best for the individual athlete.
Athletes who participate in weight-class sports—such as
wrestling or lightweight rowing—may be required to lose or
gain weight to qualify for a specific weight category.
Athletes who participate in body-conscious sports, such as
dance, gymnastics, figure skating, or diving, may be pressured to lose weight and body fat to have a lean physique,
although their current weight for health and performance is
appropriate. With extreme energy restrictions, losses of both
muscle and fat mass may adversely influence an athlete’s
performance.
Individualized assessment of an athlete’s body composition and body weight or body image may be advantageous
for the improvement of athletic performance. Age, sex,
genetics, and the requirements of the sport are factors that
impact the individual athlete’s body composition. An optimal competitive body weight and relative body fatness
should be determined when an athlete is healthy and
performing at his or her best.
Methodology and equipment to perform body composition assessments must be accessible and cost-effective. Not
all of the following methods meet these criteria for the
practitioner. In addition, athletes and coaches should know
that there are errors associated with all body composition
techniques and that it is not appropriate to set a specific
body fat percentage goal for an individual athlete. Rather, a
range of target percentages of body fat values should be
recommended.
Assessment methodology. Three levels of assessment techniques are used to assess body composition (22).
Direct assessment based on analysis of cadavers, although
not used in clinical practice, is designated as a Level 1
technique. The other two technique levels are indirect assessments (Level II) and doubly indirect assessments (Level
III). Hydrodensitometry, or underwater weighing, dualenergy x-ray absorptiometry (DXA), and air displacement
plethysmography are Level II techniques, and skinfold
measurements and bioelectrical impedance analysis (BIA)
are Level III techniques. Levels II and III techniques are
used in practice by sports dietitians.
Underwater weighing, once considered the criterion
standard, is no longer common. DXA, originally developed
to assess bone mineral, can be used for body composition
analysis (21). Although DXA is fairly accurate, quick, and
noninvasive, the cost of and access to the instrument limits
its use in practice. Air displacement plethysmography
(BodPod; Life Measurement, Inc, Concord, CA) is also
used to determine body composition by body density (22),
and body fat percentage is calculated using the equation of
either Siri (23) or Brozek (24). Although this method
provides valid and reliable assessment of body composition, it may underestimate body fat in adults and children
by 2%–3% (25).
Two of the most commonly used Level III methods are
skinfold measurements and BIA. In addition, measures of
body weight, height, wrist and girth circumferences, and
skinfold measurements are routinely used by sports dietitians
to assess body composition. Usually, seven skinfold sites are
used including abdominal, biceps, front thigh, medial calf,
subscapular, supraspinale, and triceps. The standard techniques and definitions of each of these sites are provided by
Heymsfield et al. (22) and Marfell-Jones et al. (26).
Prediction equations using skinfold measurements to determine body fat content are numerous (22). Approximately
50%–70% of the variance in body density is accounted for
by this measurement. In addition, population differences
limit the ability to interchange the prediction equations and
standardization of skinfold sites and skinfold measurement
techniques vary from investigator to investigator. Even the
skinfold caliper is a source of variability (22). Despite the
inherent problems of skinfold measurement, this technique
remains a method of choice because it is convenient and
inexpensive. The US Olympic Committee (USOC) is using
the International Society for Advances in Kinanthropometry
(ISAK) techniques (26) as efforts are underway to standardize measures worldwide. The USOC advocates using
the sum of seven skinfolds (mm) based on ISAK landmarks, marking skinfold sites on the body, reporting
duplicate measures, and communicating the results as a
range, rather than percentage of body fat.
BIA is based on the principle that an electrical signal is
more easily conducted through lean tissue than fat or bone
(22). Fat mass is estimated by subtracting the BIAdetermined estimate of FFM from total body mass. Whole
body resistance to the flow of an electrical current conducted through the body by electrodes placed on wrists and
ankles can provide fairly accurate estimates of total body
water and FFM (22). Bioelectrical impedance analysis is
dependent on several factors that can cause error in the
measurement and must be taken into account to obtain a
fairly accurate estimate. Hydration status is the most important factor that may alter the estimated percentage body
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SPECIAL COMMUNICATIONS
fat. The prediction accuracy of BIA is similar to skinfold
assessments, but BIA may be preferable because it does not
require the technical skill associated with skinfold measurements (27). Currently, upper and lower body impedance
devices have been developed but have not been evaluated in
an athletic population.
Body composition and sports performance. Body
fat percentage of athletes varies depending on the sex of the
athlete and the sport. The estimated minimal level of body
fat compatible with health is 5% for males and 12% for
females (22); however, optimal body fat percentages for an
individual athlete may be much higher than these minimums and should be determined on an individual basis. The
ISAK sum of seven skinfolds indicates that the range of
values for the athletic population is 30–60 mm for males
and 40–90 mm for females (26). Body composition analysis
should not be used as a criterion for selection of athletes for
athletic teams. Weight management interventions should be
thoughtfully designed to avoid detrimental outcomes with
specific regard for performance, as well as body composition (i.e., loss of lean body mass). See Figure 3for practical
guidelines for weight management of athletes.
FIGURE 3—Weight management strategies for athletes. Modified with
permission from: Manore MM. Chronic dieting in active women: what
are the health consequences? Womens Health Issues. 1996;6:332–41.
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Official Journal of the American College of Sports Medicine
Conclusion statement. Four studies have reported
inconclusive findings related to the effects of energy and
protein restriction on athletic performance, but carbohydrate
restriction has been shown to be detrimental. For weightclass athletes, two studies show that weight loss preceding
athletic competition may have no significant effect on
measures of performance, depending on refeeding protocol.
(Evidence Grade III = Limited). (www.adaevidencelibrary.com/conclusion.cfm?conclusion_statement_ id
=250448).
MACRONUTRIENT REQUIREMENTS
FOR EXERCISE
Athletes do not need a diet substantially different from
that recommended in the Dietary Guidelines for Americans
(16) and Eating Well with Canada’s Food Guide (28).
Although high-carbohydrate diets (more than 60% of
energy intake) have been advocated in the past, caution is
recommended in using specific proportions as a basis for
meal plans for athletes. For example, when energy intake is
4000–5000 kcalIdj1, even a diet containing 50% of the
energy from carbohydrate will provide 500–600 g of
carbohydrate (or approximately 7–8 gIkgj1 (3.2–3.6 gIlbj1)
for a 70-kg (154 lb) athlete), an amount sufficient to
maintain muscle glycogen stores from day to day (29).
Similarly, if protein intake for this plan was 10% of energy
intake, absolute protein intake (100–125 gIdj1) could
exceed the recommended protein intake for athletes (1.2–
1.7 gIkgj1Idj1 or 84–119 g in a 70-kg athlete). Conversely,
when energy intake is less than 2000 kcalIdj1, a diet
providing 60% of the energy from carbohydrate may
not be sufficient to maintain optimal carbohydrate stores
(4–5 gIkgj1 or 1.8–2.3 gIlbj1) in a 60-kg (132 lb) athlete.
Protein. Protein metabolism during and after exercise is
affected by sex, age, intensity, duration, and type of
exercise, energy intake, and carbohydrate availability. More
detailed reviews of these factors and their relationship to
protein metabolism and needs of active individuals can be
found elsewhere (30,31). The current recommended dietary
allowance (RDA) is 0.8 gIkgj1 body weight and the acceptable macronutrient distribution range (AMDR) for
protein intake for adults older than 18 yr is 10%–35% of total
calories (15). Because there is not a strong body of evidence
documenting that additional dietary protein is needed by
healthy adults who undertake endurance or resistance exercise, the current DRI for protein and amino acids does not
specifically recognize the unique needs of routinely active individuals and competitive athletes. However, recommending
protein intakes in excess of the RDA to maintain optimum
physical performance is commonly done in practice.
Endurance athletes. An increase in protein oxidation
during endurance exercise, coupled with nitrogen balance
studies, provides the basis for recommending increased
protein intakes for recovery from intense endurance training
(32). Nitrogen balance studies suggest that dietary protein
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NUTRITION AND ATHLETIC PERFORMANCE
essential fatty acids. Athletes should follow these general
recommendations. Careful evaluation of studies suggesting
a positive effect of consuming diets for which fat provides
Q70% of energy intake on athletic performance (43,44) does
not support this concept (45).
VITAMINS AND MINERALS
Micronutrients play an important role in energy production, hemoglobin synthesis, maintenance of bone health,
adequate immune function, and protection of body against
oxidative damage. They assist with synthesis and repair of
muscle tissue during recovery from exercise and injury.
Exercise stresses many of the metabolic pathways where
micronutrients are required, and exercise training may result
in muscle biochemical adaptations that increase micronutrient needs. Routine exercise may also increase the turnover
and loss of these micronutrients from the body. As a result,
greater intakes of micronutrients may be required to cover
increased needs for building, repair, and maintenance of
lean body mass in athletes (46).
The most common vitamins and minerals found to be of
concern in athletes’ diets are calcium and vitamin D, the B
vitamins, iron, zinc, magnesium, as well as some antioxidants such as vitamins C and E, A-carotene, and selenium
(46–50). Athletes at greatest risk for poor micronutrient
status are those who restrict energy intake or have severe
weight-loss practices, who eliminate one or more of the
food groups from their diet, or who consume unbalanced
and low micronutrient-dense diets. These athletes may
benefit from a daily multivitamin-and-mineral supplement.
Use of vitamin and mineral supplements does not improve
performance in individuals consuming nutritionally adequate diets (46–48, 50).
B Vitamins:Thiamin, Riboflavin, Niacin, Vitamin B6,
Pantothenic Acid, Biotin, Folate, Vitamin B12
Adequate intake of B vitamins is important to ensure
optimum energy production and the building and repair of
muscle tissue (48,51). The B-complex vitamins have two
major functions directly related to exercise. Thiamin, riboflavin, niacin, pyridoxine (B6), pantothenic acid, and biotin
are involved in energy production during exercise (46,51),
whereas folate and vitamin B12 are required for the production of red blood cells, for protein synthesis, and in
tissue repair and maintenance including the CNS. Of the B
vitamins, riboflavin, pyridoxine, folate, and vitamin B12 are
frequently low in female athletes’ diets, especially those
who are vegetarian or have disordered eating patterns
(47,48).
Limited research has been conducted to examine whether
exercise increases the need for the B-complex vitamins
(46,48). Some data suggest that exercise may slightly
increase the need for these vitamins as much as twice
the current recommended amount (48); however, these
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SPECIAL COMMUNICATIONS
intake necessary to support nitrogen balance in endurance
athletes ranges from 1.2 to 1.4 gIkgj1Idj1 (29–31). These
recommendations remain unchanged, although recent studies have shown that protein turnover may become more
efficient in response to endurance exercise training (29,32).
Ultra-endurance athletes who engage in continuous activity
for several hours or consecutive days of intermittent
exercise should also consume protein at or slightly above
1.2–1.4 gIkgj1Idj1 (32). Energy balance, or the consumption of adequate calories, particularly carbohydrates, to
meet those expended, is important to protein metabolism so
that amino acids are spared for protein synthesis and not
oxidized to assist in meeting energy needs (33,34). In
addition, discussion continues as to whether sex differences
in protein-related metabolic responses to exercise exist
(35,36).
Strength athletes. Resistance exercise may necessitate
protein intake in excess of the RDA, as well as that needed
for endurance exercise, because additional protein, essential
amino acids in particular, is needed along with sufficient
energy to support muscle growth (30,31). This is particularly true in the early phase of strength training when the
most significant gains in muscle size occurs. The amount of
protein needed to maintain muscle mass may be lower for
individuals who routinely resistance train because of more
efficient protein use (30,31). Recommended protein intakes
for strength-trained athletes range from approximately 1.2
to 1.7 gIkgj1Idj1 (30,32).
Protein and amino acid supplements. High-protein
diets have been popular throughout history. Although
earlier investigations in this area involved supplementation
with individual amino acids (37,38), more recent work has
shown that intact high-quality proteins such as whey,
casein, or soy are effectively used for the maintenance,
repair, and synthesis of skeletal muscle proteins in response
to training (39). Protein or amino acids consumed near
strength and endurance exercise can enhance maintenance
of, and net gains in, skeletal muscle (39,40). Because
protein or amino acid supplementation has not been shown
to positively impact athletic performance (41,42),
recommendations regarding protein supplementation are
conservative and directed primarily at optimizing the
training response to and the recovery period after exercise.
From a practical perspective, it is important to conduct a
thorough nutrition assessment specific to the athlete’s goals
before recommending protein powders and amino acid
supplements to athletes.
Fat. Fat is a necessary component of a normal diet,
providing energy and essential elements of cell membranes
and associated nutrients such as vitamins A, D, and E. The
acceptable macronutrient distribution range (AMDR) for fat
is 20%–35% of energy intake (17). The Dietary Guidelines
for Americans (16) and Eating Well with Canada’s Food
Guide (28) make recommendations that the proportion of
energy from fatty acids be 10% saturated, 10% polyunsaturated, 10% monounsaturated, and include sources of
209
increased needs can generally be met with higher energy
intakes. Although short-term marginal deficiencies of B
vitamins have not been observed to impact performance,
severe deficiency of vitamin B12, folate, or both may result
in anemia and reduced endurance performance (46,47,52).
Therefore, it is important that athletes consume adequate
amounts of these micronutrients to support their efforts for
optimal performance and health.
Vitamin D
Vitamin D is required for adequate calcium absorption,
regulation of serum calcium and phosphorus levels, and
promotion of bone health. Vitamin D also regulates the
development and homeostasis of the nervous system and
skeletal muscle (53–55). Athletes who live at northern
latitudes or who train primarily indoors throughout the year,
such as gymnasts and figure skaters, are at risk for poor
vitamin D status, especially if they do not consume foods
fortified with vitamin D (50,56,57). These athletes would
benefit from supplementation with vitamin D at the DRI
level (5 KgIdj1 or 200 IU for ages 19–49 yr) (54,56,58–61).
A growing number of experts advocate that the RDA for
vitamin D is not adequate (53,62,63).
SPECIAL COMMUNICATIONS
Antioxidants: Vitamins C and E, A-Carotene, and
Selenium
The antioxidant nutrients, vitamins C and E, A-carotene,
and selenium, 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 long-term exercise produces a constant
‘‘oxidative stress’’ on the muscles and other cells (49)
leading to lipid peroxidation of membranes. Although
short-term exercise may increase levels of lipid peroxide
by-products (64), habitual exercise has been shown to result
in an augmented antioxidant system and reduced lipid
peroxidation (50,65). Thus, a well-trained athlete may have
a more developed endogenous antioxidant system than a
sedentary person. Whether exercise increases the need for
antioxidant nutrients remains controversial. There is little
evidence that antioxidant supplements enhance physical
performance (49,50,64,66). Athletes at greatest risk for poor
antioxidant intakes are those following a low-fat diet,
restricting energy intakes, or limiting dietary intakes of
fruits, vegetables, and whole grains (29,66).
The evidence that a combination of antioxidants or single
antioxidants such as vitamin E may be helpful in reducing
inflammation and muscle soreness during recovery from
intense exercise remains unclear (42,67). Although the
ergogenic potential of vitamin E concerning physical
performance has not been clearly documented, endurance
athletes may have a higher need for this vitamin. Indeed,
vitamin E supplementation has been shown to reduce
lipid peroxidation during aerobic/endurance exercise and
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Official Journal of the American College of Sports Medicine
have a limited effect with strength training (66). There is
some evidence that vitamin E may attenuate exerciseinduced DNA damage and enhance recovery in certain
active individuals; however, more research is needed (66).
Athletes should be advised not to exceed the tolerable upper
intake levels (UL) for antioxidants because higher doses
could be pro-oxidative with potential negative effects
(46,64,68).
Vitamin C supplements do not seem to have an ergogenic
effect if the diet provides adequate amounts of this nutrient.
Because strenuous and prolonged exercise has been shown
to increase the need for vitamin C, physical performance
can be compromised with marginal vitamin C status or
deficiency. Athletes who participate in habitual prolonged,
strenuous exercise should consume 100–1000 mg of vitamin C daily (47,69,70).
Minerals: Calcium, Iron, Zinc, and Magnesium
The primary minerals low in the diets of athletes, especially female athletes, are calcium, iron, zinc, and magnesium (47). Low intakes of these minerals are often due to
energy restriction or avoidance of animal products (70).
Calcium. Calcium is especially important for growth,
maintenance and repair of bone tissue, maintenance of
blood calcium levels, regulation of muscle contraction,
nerve conduction, and normal blood clotting. Inadequate
dietary calcium and vitamin D increase the risk of low bone
mineral density and stress fractures. Female athletes are at
greatest risk for low bone mineral density if energy intakes
are low, dairy products and other calcium-rich foods are
inadequate or eliminated from the diet, and menstrual
dysfunction is present (47,52,55,71–73).
Supplementation with calcium and vitamin D should be
determined after nutrition assessment. Current recommendations for athletes with disordered eating, amenorrhea, and
risk for early osteoporosis are 1500 mg of elemental
calcium and 400–800 IU of vitamin D per day (50,72,73).
Iron. Iron is required for the formation of oxygencarrying proteins, hemoglobin and myoglobin, and for
enzymes involved in energy production (50,74). Oxygencarrying capacity is essential for endurance exercise as well
as normal function of the nervous, behavioral, and immune
systems (64,74). Iron depletion (low iron stores) is one of
the most prevalent nutrient deficiencies observed among
athletes, especially females (75). Iron deficiency, with or
without anemia, can impair muscle function and limit work
capacity (47,58,75,76). Iron requirements for endurance
athletes, especially distance runners, are increased by approximately 70% (58,74). Athletes who are vegetarian or
regular blood donors should aim for an iron intake greater
than their respective RDA (i.e., 18 mg and 8 mg, for men
and women respectively).
The high incidence of iron depletion among athletes is
usually attributed to inadequate energy intake. Other factors
that can impact iron status include vegetarian diets that have
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NUTRITION AND ATHLETIC PERFORMANCE
be cautioned against single-dose zinc supplements because
they often exceed this amount, and unnecessary zinc supplementation may lead to low HDL cholesterol and nutrient
imbalances by interfering with absorption of other nutrients
such as iron and copper (47). Further, the benefits of zinc
supplementation to physical performance have not been
established.
Magnesium. Magnesium plays a variety of roles in
cellular metabolism (glycolysis, fat, and protein metabolism) and regulates membrane stability and neuromuscular,
cardiovascular, immune, and hormonal functions (47,55).
Magnesium deficiency impairs endurance performance by
increasing oxygen requirements to complete submaximal
exercise. Athletes in weight-class and body-conscious
sports, such as wrestling, ballet, gymnastics, and tennis,
have been reported to consume inadequate dietary magnesium. Athletes should be educated about good food sources
of magnesium. In athletes with low magnesium status,
supplementation might be beneficial (47).
Sodium, Chloride, and Potassium
Sodium is a critical electrolyte, particularly for athletes
with high sweat losses (80–83). Many endurance athletes
will require much more than the UL for sodium (2.3 gIdj1)
and chloride (3.6 gIdj1). Sports drinks containing sodium
(0.5–0.7 gILj1) and potassium (0.8–2.0 gILj1), as well as
carbohydrate, are recommended for athletes especially in
endurance events (92 h) (50,80,82,83).
Potassium is important for fluid and electrolyte balance,
nerve transmission, and active transport mechanisms. During
intense exercise, plasma potassium concentrations tend to
decline to a lesser degree than sodium. A diet rich in a variety
of fresh vegetables, fruits, nuts/seeds, dairy foods, lean meats,
and whole grains is usually considered adequate for maintaining normal potassium status among athletes (32,83).
HYDRATION
Being well hydrated is an important consideration for
optimal exercise performance. Because dehydration
increases the risk of potentially life-threatening heat injury
such as heat stroke, athletes should strive for euhydration
before, during, and after exercise. Dehydration (loss of 92%
body weight) can compromise aerobic exercise performance, particularly in hot weather, and may impair
mental/cognitive performance (83).
The American College of Sports Medicine’s (ACSM)
Position Stand on exercise and fluid replacement (83)
provides a comprehensive review of the research and
recommendations for maintaining hydration before, during,
and after exercise. In addition, ACSM has published
position stands specific to special environmental conditions
(84,85). The major points from these position stands are the
basis for the following recommendations.
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SPECIAL COMMUNICATIONS
poor iron availability, periods of rapid growth, training at
high altitudes, increased iron losses in sweat, feces, urine,
menstrual blood, intravascular hemolysis, foot-strike hemolysis, regular blood donation, or injury (50,75,77). Athletes,
especially women, long-distance runners, adolescents, and
vegetarians should be screened periodically to assess and
monitor iron status (75,77,78).
Because reversing iron deficiency anemia can require
3–6 months, it is advantageous to begin nutrition intervention before iron deficiency anemia develops (47,75).
Although depleted iron stores (low serum ferritin) are
more prevalent in female athletes, the incidence of iron
deficiency anemia in athletes is similar to that of the
nonathlete female population (50,75,77). Chronic iron
deficiency, with or without anemia, that results from
consistently poor iron intake can negatively impact health,
physical, and mental performance and warrants prompt
medical intervention and monitoring (76,78).
Some athletes may experience a transient decrease in
serum ferritin and hemoglobin at the initiation of training
due to hemodilution after an increase in plasma volume
known as ‘‘dilutional’’ or ‘‘sports anemia’’ and may not
respond to nutrition intervention. These changes seem to be
a beneficial adaptation to aerobic training, which do not
negatively impact performance (50).
In athletes who are iron-deficient, iron supplementation
not only improves blood biochemical measures and iron
status but also increases work capacity as evidenced by
increasing oxygen uptake, reducing heart rate, and decreasing lactate concentration during exercise (47). There is
some evidence that athletes who are iron-deficient but do
not have anemia may benefit from iron supplementation
(50,75). Recent findings provide additional support for
improved performance (i.e., less skeletal muscle fatigue)
when iron supplementation was prescribed as 100-mg
ferrous sulfate for 4–6 wk (76). Improving work capacity
and endurance, increasing oxygen uptake, reducing lactate
concentrations, and reducing muscle fatigue are benefits of
improved iron status (50).
Zinc. Zinc plays a role in growth, building and repair of
muscle tissue, energy production, and immune status. Diets
low in animal protein, high in fiber and vegetarian diets, in
particular, are associated with decreased zinc intake (50,52).
Zinc status has been shown to directly affect thyroid
hormone levels, BMR, and protein use, which in turn can
negatively affect health and physical performance (50).
Survey data indicate that a large number of North
Americans have zinc intakes below recommended levels
(74,75,79). Athletes, particularly females, are also at risk for
zinc deficiency (79). The impact of low zinc intakes on zinc
status is difficult to measure because clear assessment
criteria have not been established and plasma zinc concentrations may not reflect changes in whole-body zinc status
(47,79). Decreases in cardiorespiratory function, muscle
strength, and endurance have been noted with poor zinc
status (47). The UL for zinc is 40 mg (74). Athletes should
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Fluid and Electrolyte Recommendations
Before exercise
At least 4 h before exercise, individuals should drink
j1
approximately 5–7 mLIkgj1 body weight (È2–3 mLIlb )
of water or a sport beverage. This would allow enough time
to optimize hydration status and for excretion of any excess
fluid as urine. Hyperhydration with fluids that expand
the extra- and intracellular spaces (e.g., water and glycerol
solutions) will greatly increase the risk of having to void
during competition (83) and provides no clear physiologic
or performance advantage over euhydration. This practice
should be discouraged (83).
SPECIAL COMMUNICATIONS
During exercise
Athletes dissipate heat produced during physical activity
by radiation, conduction, convection, and vaporization of
water. In hot, dry environments, evaporation accounts for
more than 80% of metabolic heat loss. Sweat rates for any
given activity will vary according to ambient temperature,
humidity, body weight, genetics, heat acclimatization state,
and metabolic efficiency. Depending on the sport and
condition, sweat rates can range from as little as 0.3 to as
much as 2.4 LIhj1 (83). In addition to water, sweat also
contains substantial but variable amounts of sodium. The
average concentration of sodium in sweat approximates
50 mmolILj1 or approximately 1 gILj1 (although concentrations vary widely). There are modest amounts of
potassium and small amounts of minerals such as
magnesium and chloride lost in sweat.
The intent of drinking during exercise is to avert a water
deficit in excess of 2% of body weight. The amount and rate
of fluid replacement is dependent on the individual athlete’s
sweat rate, exercise duration, and opportunities to drink
(83). Readers are referred to the ACSM position stand for
specific recommendations related to body size, sweat rates,
types of work, etc., and are encouraged to individualize
hydration protocols when possible (83).
Consumption of beverages containing electrolytes and
carbohydrates can help sustain fluid and electrolyte balance
and endurance exercise performance (83). The type,
intensity, and duration of exercise and environmental
conditions will alter the need for fluids and electrolytes.
Fluids containing sodium and potassium help replace sweat
electrolyte losses, whereas sodium stimulates thirst and
fluid retention and carbohydrates provides energy. Beverages containing 6%–8% carbohydrate are recommended for
exercise events lasting longer than 1 h (83).
Fluid balance during exercise is not always possible
because maximal sweat rates exceed maximal gastric
emptying rates that in turn limit fluid absorption, and most
often, rates of fluid ingestion by athletes during exercise fall
short of amounts that can be emptied from the stomach and
absorbed by the gut. Gastric emptying is maximized when
the amount of fluid in the stomach is high and reduced with
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Official Journal of the American College of Sports Medicine
hypertonic fluids or when carbohydrate concentration is
greater than 8%.
Disturbances of fluid and electrolyte balance that can
occur in athletes include dehydration, hypohydration, and
hyponatremia (83). Exercise-induced dehydration develops
because of fluid losses that exceed fluid intake. Although
some individuals begin exercise euhydrated and dehydrate
over an extended duration, athletes in some sports might
start training or competing in a dehydrated state because
the interval between exercise sessions is inadequate for
full rehydration (82). Another factor that may predispose an
athlete to dehydration is ‘‘making weight’’ as a prerequisite
for a specific sport or event. Hypohydration, a practice of
some athletes competing in weight-class sports (i.e.,
wrestling, boxing, lightweight crew, martial arts, etc.), can
occur when athletes dehydrate themselves before beginning
a competitive event. Hypohydration can develop by fluid
restriction, certain exercise practices, diuretic use, or sauna
exposure before an event. In addition, fluid deficits may
span workouts for athletes who participate in multiple or
prolonged daily sessions of exercise in the heat (84).
Hyponatremia (serum sodium concentration less than
130 mmolILj1) can result from prolonged, heavy sweating
with failure to replace sodium, or excessive water intake.
Hyponatremia is more likely to develop in novice marathoners who are not lean, who run slowly, who sweat less, or who
consume excess water before, during, or after an event (83).
Skeletal muscle cramps are associated with dehydration,
electrolyte deficits, and muscle fatigue. Non–heat-acclimatized
American football players commonly experience dehydration
and muscle cramping particularly during formal preseason
practice sessions in late summer. Athletes participating in
tennis matches, long-cycling races, late-season triathlons,
soccer, and beach volleyball are also susceptible to dehydration and muscle cramping. Muscle cramps also occur in
winter-sport athletes such as cross-country skiers and ice
hockey players. Muscle cramps are more common in profuse
sweaters who experience large sweat sodium losses (83).
After exercise
Because many athletes do not consume enough fluids
during exercise to balance fluid losses, they complete their
exercise session dehydrated to some extent. Given adequate
time, intake of normal meals and beverages will restore
hydration status by replacing fluids and electrolytes lost
during exercise. Rapid and complete recovery from excessive dehydration can be accomplished by drinking at least
16–24 oz (450–675 mL) of fluid for every pound (0.5 kg) of
body weight lost during exercise. Consuming rehydration
beverages and salty foods at meals/snacks will help replace
fluid and electrolyte losses (83).
Special Environmental Conditions
Hot and humid environments. The risk for dehydration and heat injury increases dramatically in hot, humid
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212
environments (84). When the ambient temperature exceeds
body temperature, heat cannot be dissipated by radiation.
Moreover, the potential to dissipate heat by evaporation of
sweat is substantially reduced when the relative humidity is
high. There is a very high risk of heat illness when temperature and humidity are both high. If competitive events occur
under these conditions, it is necessary to take every precaution
to ensure that athletes are well hydrated, have ample access to
fluids, and are monitored for heat-related illness.
Cold environments. It is possible for dehydration to
occur in cool or cold weather (85). Factors contributing to
dehydration in cold environments include respiratory fluid
losses and sweat losses that occur when insulated clothing
is worn during intense exercise. Dehydration can also occur
because of low rates of fluid ingestion. If an athlete is
chilled and available fluids are cold, the incentive to drink
may be reduced. Finally, removal of multiple layers of
clothing to urinate may be inconvenient and difficult for
some athletes, especially women, and they may voluntarily
limit fluid intake (86).
Altitude. Fluid losses beyond those associated with
any exercise performed may occur at altitudes 92500 m
(8200 ft) consequent to mandatory diuresis and high
respiratory water losses, accompanied by decreased appetite. Respiratory water losses may be as high as 1900
mLIdj1 (1.9 LIdj1) in men and 850 mLIdj1 (0.85 LIdj1) in
women (87,88). Total fluid intake at high altitude
approaches 3–4 LIdj1 to promote optimal kidney function
and maintain urine output of È1.4 L in adults (87).
THE TRAINING DIET
NUTRITION AND ATHLETIC PERFORMANCE
Pre-Exercise Meal
Eating before exercise, as opposed to exercising in the
fasting state, has been shown to improve performance
(89,90). The meal or snack consumed before competition or
an intense workout should prepare athletes for the upcoming activity and leave the individual neither hungry nor
with undigested food in the stomach. Accordingly, the following general guidelines for meals and snacks should be
used: sufficient fluid should be ingested to maintain hydration, foods should be relatively low in fat and fiber to
facilitate gastric emptying and minimize gastrointestinal
distress, high in carbohydrate to maintain blood glucose and
maximize glycogen stores, moderate in protein, and familiar
to the athlete.
The size and timing of the pre-exercise meal are interrelated. Because most athletes do not like to compete on a full
stomach, smaller meals should be consumed near the event to
allow for gastric emptying, whereas larger meals can be consumed when more time is available before exercise or competition. Amounts of carbohydrate shown to enhance
performance have ranged from approximately 200 to 300 g
of carbohydrate for meals consumed 3–4 h before exercise. Studies report either no effect or beneficial effects of
Medicine & Science in Sports & Exercised
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SPECIAL COMMUNICATIONS
The fundamental differences between an athlete’s diet
and that of the general population are that athletes require
additional fluid to cover sweat losses and additional energy to fuel physical activity. As discussed earlier, it is
appropriate for much of the additional energy to be supplied
as carbohydrate. The proportional increase in energy
requirements seems to exceed the proportional increase in
needs for most other nutrients. Accordingly, as energy
requirements increase, athletes should first aim to consume
the maximum number of servings appropriate for their
needs from carbohydrate-based food groups (bread, cereals
and grains, legumes, milk/alternatives, vegetables, and
fruits). Energy needs for many athletes will exceed the
amount of energy (kcalIdj1) in the upper range of servings for these food groups. Conversely, athletes who are
small and/or have lower energy needs will need to pay
greater attention to making nutrient-dense food choices
to obtain adequate carbohydrate, protein, essential fats, and
micronutrients.
With regard for the timing of meals and snacks, common
sense dictates that food and fluid intake around workouts be
determined on an individual basis with consideration for an
athlete’s gastrointestinal characteristics as well as the
duration and intensity of the workout. For example, an
athlete might tolerate a snack consisting of milk and a
sandwich 1 h before a low-intensity workout but would be
uncomfortable if the same meal was consumed before a
very hard effort. Athletes in heavy training or doing
multiple daily workouts may need to eat more than three
meals and three snacks per day and should consider every
possible eating occasion. These athletes should consider
eating near the end of a workout, having more than one
afternoon snack, or eating a substantial snack before bed.
Conclusion statement. Twenty-three studies investigating consumption of a range of macronutrient composition
during the training period on athletic performance were
evaluated. Nine studies have reported that the consumption
of a high-carbohydrate diet (960% of energy) during
the training period and the week before competition results
in improved muscle glycogen concentrations and/or significant improvements in athletic performance. Two studies
reported no additional performance benefits when consuming level above 6 g carbohydratesIkgj1 body weight. Two
studies report sex differences; women may have less ability
to increase muscle glycogen concentrations through increased carbohydrate consumption, especially when energy
intake is insufficient. One study based on the consumption
of a high-fat diet (965% of energy) for 10 d followed by
a high-carbohydrate diet (965% of energy) for 3 d reported
a significant improvement in athletic performance. Nine
studies report no significant effects of macronutrient composition on athletic performance during the training period
and week before competition. (Evidence Grade II = Fair).
(www.adaevidencelibrary.com/conclusion.cfm?conclusion_
statement_id=250447).
213
pre-event feeding on performance (91–98). Data are equivocal concerning whether the glycemic index of carbohydrate
in the pre-exercise meal affects performance (92,99–102).
Although the above guidelines are sound and effective,
the athlete’s individual needs must be emphasized. Some
athletes consume and enjoy a substantial meal (e.g., pancakes, juice, and scrambled eggs) 2–4 h before exercise or
competition; however, others may experience severe gastrointestinal distress after such a meal and need to rely on
liquid meals. Athletes should always ensure that they know
what works best for themselves by experimenting with new
foods and beverages during practice sessions and planning
ahead to ensure they will have access to these foods at the
appropriate time.
Conclusion statement. Nineteen studies investigating
the consumption of a range of macronutrient composition
during the 24 h before competition on athletic performance
were evaluated. Of eight studies, six reported no significant
effect of meal consumption 90 min to 4 h before trials on
athletic performance. Six studies that focused on the
consumption of food or beverage within the hour before
competition reported no significant effects on athletic
performance, despite hyperglycemia, hyperinsulinemia,
increased carbohydrate oxidation, and reduced free fatty
acid availability. Variations in research methodology on
glycemic index of meals consumed before competition have
led to inconclusive findings. (Evidence Grade II = Fair).
(www.adaevidencelibrary.com/conclusion.cfm?conclusion_
statement_id=250452).
SPECIAL COMMUNICATIONS
During Exercise
Current research supports the benefit of carbohydrate
consumption in amounts typically provided in sport drinks
(6%–8%) to endurance performance in events lasting 1 h or
less (103–105), especially in athletes who exercise in the
morning after an overnight fast when liver glycogen levels
are decreased. Providing exogenous carbohydrate during
exercise helps maintain blood glucose levels and improve
performance (106).
For longer events, consuming 0.7 g carbohydratesIkgj1
body weightIhj1 (approximately 30–60 gIhj1) has been
shown unequivocally to extend endurance performance
(107,108). Consuming carbohydrates during exercise is
even more important in situations when athletes have not
carbohydrate-loaded, not consumed pre-exercise meals, or
restricted energy intake for weight loss. Carbohydrate
intake should begin shortly after the onset of activity;
consuming a given amount of carbohydrate as a bolus after
2 h of exercise is not as effective as consuming the same
amount at 15- to 20-min intervals throughout the 2 h of
activity (109). The carbohydrate consumed should yield
primarily glucose; fructose alone is not as effective and may
cause diarrhea, although mixtures of glucose and fructose,
other simple sugars and maltodextrins, seem effective (107).
If the same total amount of carbohydrate and fluid is
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Official Journal of the American College of Sports Medicine
ingested, the form of carbohydrate does not seem to matter.
Some athletes may prefer to use a sport drink, whereas
others may prefer to consume a carbohydrate snack or
sports gel and consume water. As described elsewhere in
this document, adequate fluid intake is also essential for
maintaining endurance performance.
Conclusion statement. Thirty-six studies investigating the consumption of a range of macronutrient composition during competition on athletic performance were
evaluated. Seven studies based on carbohydrate consumption during exercise lasting less than 60 min show
conflicting results on athletic performance. However, of
17 studies based on carbohydrate consumption during
exercise lasting greater than 60 min, 5 reported improved
metabolic response, and 7 of 12 studies reported improvements in athletic performance. Evidence is inconclusive regarding the addition of protein to carbohydrate
during exercise on athletic performance. Seven studies
based on consumption of pre-exercise meals in addition to
carbohydrate consumption during exercise suggest enhanced athletic performance. (Evidence Grade II = Fair).
(www.adaevidencelibrary.com/conclusion.cfm?conclusion_
statement_id=250453).
Recovery
The timing and composition of the postcompetition or
postexercise meal or snack depend on the length and
intensity of the exercise session (i.e., whether glycogen
depletion occurred) and on when the next intense workout
will occur. For example, most athletes will finish a
marathon with depleted glycogen stores, whereas glycogen
depletion would be less marked after a 90-min training run.
Because athletes competing in a marathon are not likely to
perform another race or hard workout the same day, the
timing and composition of the postexercise meal is less
critical for these athletes. Conversely, a triathlete participating in a 90-min run in the morning and a 3-h cycling
workout in the afternoon needs to maximize recovery
between training sessions. The postworkout meal assumes
considerable importance in meeting this goal.
Timing of postexercise carbohydrate intake affects
glycogen synthesis over the short term (110). Consumption
of carbohydrates within 30 min after exercise (1.0–1.5 g
carbohydrateIkgj1 at 2-h intervals up to 6 h is often
recommended) results in higher glycogen levels after
exercise than when ingestion is delayed for 2 h (111). It is
unnecessary for athletes who rest one or more days between
intense training sessions to practice nutrient timing about
glycogen replenishment provided sufficient carbohydrates
are consumed during the 24-h period after the exercise bout
(112). Nevertheless, consuming a meal or snack near the
end of exercise may be important for athletes to meet daily
carbohydrate and energy goals.
The type of carbohydrate consumed also affects postexercise glycogen synthesis. When comparing simple sugars,
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214
glucose and sucrose seem equally effective when consumed
at a rate of 1.0–1.5 gIkgj1 body weight for 2 h; fructose
alone is less effective (113). With regard to whole foods,
consumption of carbohydrate with a high glycemic index
results in higher muscle glycogen levels 24 h after a
glycogen-depleting exercise as compared with the same
amount of carbohydrates provided as foods with a low glycemic index (114). Application of these findings, however,
must be considered in conjunction with the athlete’s overall
diet. When isocaloric amounts of carbohydrates or carbohydrates plus protein and fat are provided after endurance
(115) or resistance exercise (116), glycogen synthesis rates
are similar. Including protein in a postexercise meal,
however, may provide needed amino acids for muscle
protein repair and promote a more anabolic hormonal
profile (33).
Conclusion statement. Twenty-five studies investigating the consumption of a range of macronutrient composition during the recovery period were evaluated. Nine
studies report that consumption of diets higher in carbohydrate (965% carbohydrate or 0.8–1.0 g carbohydratesIkgj1
body weightIhj1) during the recovery period increases
plasma glucose and insulin concentrations and increases
muscle glycogen resynthesis. Provided that carbohydrate
intake is sufficient, four studies show no significant benefit
of additional protein intake and two studies show no
significant effect of meal timing on muscle glycogen
resynthesis during the recovery period. Studies focusing
on carbohydrate consumption during recovery periods of 4
h or more suggest improvements in athletic performance.
(Evidence Grade II = Fair). (www.adaevidencelibrary.com/
conclusion.cfm?conclusion_statement_id=250451).
DIETARY SUPPLEMENTS AND
ERGOGENIC AIDS
NUTRITION AND ATHLETIC PERFORMANCE
Medicine & Science in Sports & Exercised
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721
SPECIAL COMMUNICATIONS
The overwhelming number and increased availability of
sports supplements presents an ongoing challenge for the
practitioner and the athlete to keep up-to-date about the
validity of the claims and scientific evidence. Although
dietary supplements and nutritional ergogenic aids, such as
nutritional products that enhance performance, are highly
prevalent, the fact remains that very few improve performance (117–119) and some may cause concern.
In the United States, the Dietary Supplements and Health
Education Act of 1994 allows supplement manufacturers to
make health claims regarding the effect of products on body
structure or function but not therapeutic claims to ‘‘diagnose, mitigate, treat, cure, or prevent’’ a specific disease or
medical condition (117,120). As long as a special supplement label indicates the active ingredients and the entire
ingredients list is provided, claims for enhanced performance can be made, valid or not. The Act, however, made
the FDA responsible for evaluating and enforcing safety. In
2003, the US/FDA Task Force on Consumer Health
Information for Better Nutrition proposed a new system
for evaluating health claims that uses an evidence-based
model and is intended to help consumers determine
effectiveness of ergogenic aids and dietary supplements
more reliably (117). Although all manufacturers are
required by the FDA to analyze the identity, purity, and
strength of all of their products’ ingredients, they are not
required to demonstrate the safety and efficacy of their
products.
Canada regulates supplements as medicine or as natural health products (NHP). Products regulated in Canada
as NHP must comply with Natural Health Products
Regulations (2003) and manufacturers are allowed to make
a full range of claims (structure/function, risk reduction,
treatment, prevention) as supported by scientific evidence
(117). In Canada, sports supplements such as sport drinks,
protein powders, energy bars, and meal replacement products/beverages are regulated by Health Canada’s Canadian
Food Inspection Agency, whereas energy drinks, vitamin/
mineral and herbal supplements, vitamin-enhanced water,
and amino acid supplements fall under the NHP Regulations.
Anabolic steroids are considered drugs and are tightly
regulated under the Controlled Drugs & Substances Act.
Sports dietitians should consider the following factors in
evaluating nutrition-related ergogenic aids: validity of the
claims relative to the science of nutrition and exercise, quality
of the supportive evidence provided (double-blinded, placebocontrolled scientific studies vs testimonials), and health and
legal consequences of the claim (121,122). The safety of
ergogenic aids remains in question. Possible contamination
of dietary supplements and ergogenic aids with banned or
nonpermissable substances remains an issue of concern.
Therefore, sports dietitians and athletes must proceed with
caution when considering the use of these types of products.
Ultimately, athletes are responsible for the product they
ingest and any subsequent consequences. Dietary supplements or ergogenic aids will never substitute for genetic
makeup, years of training, and optimum nutrition.
Both national [National Collegiate Athletic Association
(NCAA; www.ncaa.org), United States Anti-Doping Agency
(www.usantidoping.org)] and international sports organizations
[World Anti-Doping Agency (WADA; (www.wada-ama.org)]
limit the use of certain ergogenic aids and require random urine
testing of athletes to ensure that certain products are not
consumed. In Canada, the Canadian Centre for Ethics in Sport
(www.cces.ca) is the organization which checks for banned
substances.
The ethical use of performance-enhancing substances is a
personal choice and remains controversial (117). Therefore,
it is important that the qualified sports nutrition professional
keep an open mind when working with elite athletes to
effectively assess, recommend, educate, and monitor athletes who contemplate using or actively take dietary supplements and/or ergogenic aids (117). Credible and
responsible information regarding the use of these products
should be made available by qualified health professionals
215
such as Board Certified Specialists in Sports Dietetics
(CSSD) who carefully evaluate the risk–benefit ratio,
including a complete dietary assessment.
It is beyond the scope of this article to address the
multitude of ergogenic aids used by athletes in North
America. From a practical perspective, however, most
ergogenic aids can be classified into one of four categories:
1. those that perform as claimed; 2. those that may perform
as claimed but for which there is insufficient evidence of
efficacy at this time; 3. those that do not perform as
claimed; and 4. those that are dangerous, banned, or illegal
and, therefore, should not be used (122).
SPECIAL COMMUNICATIONS
1. Ergogenic aids that perform as claimed
Creatine. Creatine is currently the most widely used
ergogenic aid among athletes wanting to build muscle and
enhance recovery (118,123–125). Creatine has been shown
to be effective in repeated short bursts of high-intensity
activity in sports that derive energy primarily from the
ATP-CP energy system such as sprinting and weight lifting
but not for endurance sports such as distance running
(32,117,126–128). Most of the researches on creatine have
been conducted in a laboratory setting with male athletes.
The most common adverse effects of creatine supplementation are weight (fluid) gain, cramping, nausea, and
diarrhea (32,117,129). Although widely debated, creatine is
generally considered safe for healthy adults, despite
anecdotal reports of dehydration, muscle strains/tears, and
kidney damage (130–132). Although the effects of longterm use of creatine remain unknown, studies to date do not
show any adverse effects in healthy adults from creatine
supplementation (133). Nevertheless, health care professionals should carefully screen athletes using creatine for any
risk of liver or kidney dysfunction or, in rare instances,
anterior compartment syndrome.
Caffeine. The potential ergogenic effects of caffeine may
be more closely related to its role as a CNS stimulant and the
associated decreased perception of effort as opposed to its
role in mobilizing of free fatty acids and sparing of muscle
glycogen (117,134). In 2004, WADA moved caffeine from
the restricted list to its Monitoring Programme. However,
caffeine is still a restricted substance by the NCAA, where a
positive doping test would be a caffeine level 915 KgImLj1
of urine. New evidence shows that caffeine, when used in
moderation, does not cause dehydration or electrolyte
imbalance (135–138). However, when rapid hydration is
necessary, athletes should rely on noncaffeinated and
nonalcoholic beverages.
The use of high-energy drinks containing caffeine can be
ergolytic and potentially dangerous when used in excess or
in combination with stimulants or alcohol or other unregulated herbals and should be discouraged (32,117,139–
141). Adverse effects of caffeine are anxiety, jitteriness,
rapid heartbeat, gastrointestinal distress, and insomnia, and
it could be ergolytic for novice users (134,142). There is
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Official Journal of the American College of Sports Medicine
little evidence to promote use of caffeine alone as a weightloss aid (118).
Sports drinks, gels, and bars. Sports drinks, gels, and
bars are commonly used as convenient dietary supplements
or ergogenic aids for busy athletes and active people. It is
important that qualified nutrition professionals educate
consumers about label reading, product composition, and
appropriate use of these products (before, during, and after
training and competition).
Sodium bicarbonate. Sodium bicarbonate may be an
effective ergogenic aid as a blood buffer (role in acid–base
balance and prevention of fatigue), but its use is not
without unpleasant adverse effects such as diarrhea
(117,143).
Protein and amino acid supplements. Current evidence indicates that protein and amino acid supplements are
no more or no less effective than food when energy is
adequate for gaining lean body mass (30,31,117). Although
widely used, protein powders and amino acid supplements
are a potential source for illegal substances such as
nandrolone, which may not be listed on the ingredient label
(144,145).
2. Ergogenic aids that may perform as claimed but for
which there is insufficient evidence
The ergogenic aids that have claims as health and
performance enhancers include glutamine, A-hydroxymethylbutyrate, colostrum, and ribose (117). Preliminary
studies concerning these ergogenic aids are inconclusive
as performance enhancers. These substances are not banned
from use by athletes (www.wada-ama.org/en/prohibited
list.ch2).
3. Ergogenic aids that do not perform as claimed
The majority of ergogenic aids currently on the market
are in this category (122). These include amino acids, bee
pollen, branched chain amino acids, carnitine, chromium
picolinate, cordyceps, coenzyme Q10, conjugated linoleic
acid, cytochrome C, dihydroxyacetone, F-oryzanol, ginseng, inosine, medium-chain triglycerides, pyruvate, oxygenated water, and vanadium. This list is by no means
exhaustive, and it is likely that other substances would be
best placed in this category. Similarly, it is possible for any
of these compounds to eventually move from this to another
category after appropriate scientific inquiry and evaluation. To date, however, none of these products has been
shown to enhance performance and many have had adverse
effects (122).
4. Ergogenic aids that are dangerous, banned, or illegal
The ergogenic aids in this category should not be used
and are banned by WADA. Examples are androstenedione,
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216
dehydroepiandrosterone, 19-norandrostenedione, 19-norandrostenediol, and other anabolic, androgenic steroids,
Tribulus terrestris, ephedra, strychnine, and human growth
hormone. Because this is an evolving field, sports dietitians
need to consistently consider the status of various nutritional ergogenic aids.
The Vegetarian Athlete
NUTRITION AND ATHLETIC PERFORMANCE
Roles and Responsibilities of the Sports Dietitian
As nutrition information advances in quantity and
complexity, athletes and active individuals are presented
with a myriad of choices and decisions about appropriate
and effective nutrition for activity and performance.
Increasingly, athletes and active individuals seek professionals to guide them in making optimal food and fluid
choices. Although many athletes and active individuals
view winning or placing in an event to be the ultimate
evidence of the effectiveness of their dietary regimens,
sports dietitians should address the combined goals of
health and fitness, enhanced capacity to train, and optimal
athletic performance. Therefore, sports dietitians should be
competent in the following areas:
Roles
Conduct comprehensive nutrition assessment and
consultation
Educate in food selection, purchasing, and preparation
Provide medical nutrition therapy in private practice,
health care, and sports settings
Identify and treat nutritional issues that impact health
and performance
Address energy balance and weight management issues
Address nutritional challenges to performance (gastrointestinal disturbances, iron depletion, eating disorders,
female athlete triad, food allergies, and supplement use)
Track and document measurable outcomes of nutrition
services
Promote wound and injury healing
Oversee menu planning and design, including pre- and
postevent and travel
Develop and oversee nutrition polices and procedures
Evaluate the scientific literature and provide evidencebased assessment and application
Responsibilities
Apply sports nutrition science to fueling fitness and
performance
Develop personalized nutrition and hydration strategies
Advise on dietary supplements, ergogenic aids, meal
and fluid replacement products, sports drinks, bars,
and gels
Medicine & Science in Sports & Exercised
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723
SPECIAL COMMUNICATIONS
The Position Statement of the American Dietetic Association and Dietitians of Canada on vegetarian diets (2003)
provides appropriate dietary guidance for vegetarian athletes. This article provides additional considerations for
vegetarians who participate in exercise. Well-planned vegetarian diets seem to effectively support parameters that
influence athletic performance, although studies on this
population are limited (31,146). Plant-based high-fiber diets
may reduce energy availability. Monitoring body weight and
body composition is the preferred means of determining
whether energy needs are met. Some individuals, especially
women, may switch to vegetarianism as a means of avoiding
red meat and/or restricting energy intake to attain a lean body
composition favored in some sports. Occasionally, this may
be a red flag for disordered eating and increase the risk for
the female athlete triad (72,73). Because of this association,
coaches, trainers, and other health professionals should be
alert when an athlete becomes a vegetarian and should ensure
that appropriate weight is maintained.
Although most vegetarian athletes meet or exceed
recommendations for total protein intake, their diets often
provide less protein than those of nonvegetarians (31).
Thus, some individuals may need more protein to meet
training and competition needs (31). Protein quality of
plant-based diets should be sufficient provided a variety of
foods that supply adequate energy is consumed (31).
Protein quality is a potential concern for individuals who
avoid all animal proteins such as milk and meat (i.e.,
vegans). Their diets may be limited in lysine, threonine,
tryptophan, or methionine (39).
Because plant proteins are less well digested than animal
proteins, an increase in intake of approximately 10%
protein is advised (15). Therefore, protein recommendations
for vegetarian athletes approximate 1.3–1.8 gIkgj1Idj1
(52). Vegetarians with relatively low energy intakes should
choose foods wisely to ensure protein intakes are consistent
with these recommendations.
Vegetarian athletes may be at risk for low intakes of
energy, fat, vitamins B12, riboflavin, and D, calcium, iron,
and zinc, which are readily available from animal proteins.
Iron is of particular concern because of the low bioavailability of nonheme plant sources. Iron stores of vegetarians
are generally lower than omnivores (52). Vegetarian athletes, especially women, may be at greater risk for developing iron deficiency or anemia. Routine monitoring of
iron status is recommended for vegetarian athletes, especially during periods of rapid growth (i.e., adolescence
and pregnancy). Very low fat diets or avoidance of all
animal protein may lead to a deficiency of essential fatty
acids. Sport dietitians should educate novice vegetarian
athletes on resources for menu planning, cooking, and
shopping—especially high-quality plant protein combinations and acceptable animal sources (i.e., dairy and eggs) as
well as foods rich in or fortified with key nutrients (calcium,
vitamins D, B12, and riboflavin, iron, and zinc) (52).
217
SPECIAL COMMUNICATIONS
Evaluate dietary supplements and sports foods for
legality, safety, and efficacy
Provide nutrition strategies to delay fatigue during
exercise and speed recovery from training
Help enhance athletic training capacity and performance
Participate in identifying and treating disordered eating
patterns
Provide nutrition strategies to reduce risk of illness/
injury and facilitate recovery
Promote career longevity for collegiate and professional athlete and all active individuals
Recruit and retain clients and athletes in practice
Provide sports nutrition as member of multidisciplinary/medical/health care teams
Provide reimbursable services (diabetes medical nutrition therapy)
Design and conduct sports team education
Serve as a mentor for developing sports dietetics
professionals
Maintain credential(s) by actively engaging in profession-specific continuing education activities
The aforementioned responsibilities should be routine
expectations of sporting and sports medicine organizations
that employ qualified sports dietitians and of clients and
athletes seeking valid sports nutrition information and advice.
In 2005, the Commission on Dietetic Registration (CDR;
the credentialing agency of the American Dietetic Association) created a specialty credential for food and nutrition
professionals who specialize in sports dietetic practice. The
Board Certification Specialist in Sports Dietetics (CSSD)
credential is designed as the premier professional sports
nutrition credential in the United States. Specialists in Sports
Dietetics provide safe, effective, evidence-based nutrition
assessment, guidance, and counseling for health and performance for athletes, sport organizations, and physically active
individuals and groups. The credential requires current
Registered Dietitian (RD) status, maintenance of RD status
for a minimum of 2 yr, and documentation of 1500 sports
specialty practice hours as an RD within the past 5 yr. For
more information, readers are referred to the following Web
site: www.cdrnet.org/whatsnew/Sports.htm.
ADA/DC/ACSM position adopted by the ADA House of
Delegates Leadership Team on July 12, 2000 and reaffirmed on May 25, 2004; approved by Dietitians of Canada
on July 12, 2000 and approved by the American College of
Sports Medicine Board of Trustees on October 17, 2000.
The Coaching Association of Canada endorses this position
paper. This position is in effect until December 31, 2012.
ADA/DC/ACSM authorizes republication of the position, in
its entirety, provided full and proper credit is given. Readers
may copy and distribute this article, providing such
distribution is not used to indicate an endorsement of
product or service. Commercial distribution is not permitted
without the permission of ADA. Requests to use portions
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Official Journal of the American College of Sports Medicine
of the position must be directed to ADA headquarters at
800/877-1600, ext 4835, or [email protected].
AUTHORS
- American College of Sports Medicine: Nancy R. Rodriguez, PhD,
RD, CSSD, FACSM (University of Connecticut, Storrs, CT)
- American Dietetic Association: Nancy M. DiMarco, PhD, RD,
CSSD, FACSM (Texas Woman’s University, Denton, TX)
- Dietitians of Canada: Susie Langley, MS, RD, CSSD (69 McGill
Street, Toronto, ON, Canada)
REVIEWERS
- American Dietetic Association:
Sharon Denny, MS, RD (ADA Knowledge Center, Chicago, IL);
Mary H. Hager, PhD, RD, FADA (ADA Government Relations,
Washington, DC)
Melinda M. Manore, PhD, RD, CSSD (Oregon State University,
Corvallis, OR)
Esther Myers, PhD, RD, FADA (ADA Scientific Affairs, Chicago, IL);
Nanna Meyer, PhD, RD, CSSD (University of Colorado, Colorado
Springs, CO)
James Stevens, MS, RD (Metropolitan State College of Denver,
Denver, CO)
Jennifer A. Weber, MPH, RD (ADA Government Relations,
Washington, DC)
- Dietitians of Canada:
Rennie Benedict, MSc, RD (Department of Kinesiology & Applied
Health, University of Winnipeg, Winnipeg, MB)
Marilyn Booth, MSc, RD (Registered Dietitian and Exercise
Consultant, Ottawa, ON)
Patricia Chuey, MSc, RD (Manager Nutrition Affairs, Overwaitea
Food Group, Vancouver, BC)
Kelly Anne Erdman, MSc, RD (University of Calgary Sport
Medicine Centre, Calgary AB)
Marielle Ledoux, PhD, PDt (Department of Nutrition, Faculty of
Medicine, Université de Montréal, QC)
Heather Petrie, MSc, PDt (Nutrition Cosultant, Halifax, NS)
Pamela Lynch, MHE, PDt (Nutrition Counseling Services &
Associates; Mount Saint Vincent University, Department of Applied
Human Nutrition, Halifax, NS)
Elizabeth (Beth) Mansfield, MSc, RD, PhD Candidate (McGill
University, Montreal, QC)
American College of Sports Medicine:
Susan Barr, PhD, RDN (University of British Columbia, Vancouver, BC)
Dan Benardot, PhD, DHC, RD (Georgia State University, Atlanta,
GA)
Jacqueline Berning, PhD, RD (University of Colorado Springs,
Colorado Springs, CO)
Andrew Coggan, PhD (Washington University School of Medicine, St. Louis, MO)
Melinda Manore, PhD, RD (Oregon State University, Corvallis,
OR)
Brian Roy, PhD (Brock University, St. Catharines, ON)
Assistance from Lisa M. Vislocky, PhD, University of Connecticut,
Storrs, CT, in preparing the references is acknowledged.
APC WORKGROUP
Christine M. Palumbo, MBA, RD (chair); Pat M. Schaaf, MS, RD;
Doug Kalman, PhD, RD, FACN (content advisor); Roberta Anding,
MS, RD, LD, CDE, CSSD (content advisor).
The authors thank the reviewers for their many constructive
comments and suggestions. The reviewers were not asked to
endorse this position or the supporting paper.
http://www.acsm-msse.org
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218
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Strength and Conditioning Journal: Vol. 21, No. 1, pp. 14–23.
Creatine Controversy?
Steven S. Plisk, MS, CSCS
Department of Athletics, Physical Education and Recreation, Yale University
Richard B. Kreider, PhD, FACSM
Department of Human Movement Sciences and Education, University of Memphis
Description and Function
Many nutritional supplements-and accompanying performance/ health claims-come and go without much commotion,
but none has ever generated the kind of interest or debate surrounding creatine (Cr). Some proponents advocate it as a
panacea, whereas opponents assert that it is harmful, and of course plenty of rumor and half-truth always arises
between such polarized viewpoints. Compounding the problem is the fact that, in addition to its bioenergetic role, Cr
has muscle-building properties, thereby contributing to the misperception of it as just another crash weight-gain
powder or steroid alternative. This article is intended to clarify what is known about Cr's physiologic role and the
effects of supplementation. Directions for further research and hypothetical guidelines on its use will also be
proposed.
It is important to know the why’s before the how’s, so let's review some basic background information (1, 9,
10–13, 17, 26, 38, 39):
•
Cr is present in meat, fish and poultry (3–9 g/kg) and is absorbed intact by the gut when ingested (with a
mixed diet usually accounting for about half the daily need).
•
Cr is synthesized in the kidney, liver, and pancreas (2 g/d) from amino acid precursors arginine, glycine,
and methionine.
•
Once released into the bloodstream, CR is taken up via insulin-modulated active transport, stored (at a
ratio of 3:2 [PCr]/[Cr]), and used by tissues with explosive or variable energy demands, especially the
neuromuscular system and heart (accounting for 95%, with the remainder in the brain and testes).
Although it is commonly known that Cr participates in the high-energy phosphagen system (6), this is an
oversimplification that does not fully explain its function.
PCr Circuit
A muscle cell's interior is a designed system of integrated, coadaptive processes where metabolites are channeled
through coupled reactions and multi-enzyme complexes (14, 15, 30–34, 40, 41, 43). Intrinsic to this model is the
creatine kinase–phosphocreatine (CK-PCr) system, a highly organized and compartmentalized circuit with at least two
distinct functions (2, 3, 5, 17, 18, 23, 27, 29–35, 39–43).
Energy Buffering. Adenine nucleotides, including ADP and ATP, are maintained in relatively low
concentrations because they are heavy, negatively charged compounds that would disrupt ionic/osmotic balance if
present in high concentrations (6, 15). This has strategic importance in terms of metabolic control because the ratio of
tissue ATP: ADP concentrations (i.e., [ATP]/[ADP]) is a key modulator of many fundamental pathways, and
regulatory sensitivity is improved by storing them at low levels. However, Cr and PCr are smaller and less negatively
charged compounds (allowing them to be stored at resting concentrations several-fold that of ATP) that are involved
in only one reaction (CK), making it another ideal control pathway. In terms of buffering high-energy demands, PCr
is the capacitor of choice by virtue of its free energy of hydrolysis and other properties (6, 14, 15), including the
following:
•
Stability at high concentrations.
•
Rapid mobilization.
•
Minimal effect on ATP pools (or osmotic/ionic balance).
•
Nondeleterious end products.
•
Useful ancillary roles (e.g., in oxidative metabolism, as described below).
226
Energy Transport/Distribution.. The high concentration and diffusibility of PCr and Cr in comparison with
ATP and ADP allow the CK-PCr system to effectively channel phosphagens between sites of energy production (i.e.,
mitochondria, glycolysis) and consumption (i.e., ATPases). [ATP] and [ADP] are thereby stabilized, improving
thermodynamic efficiency and metabolic regulation (18, 30–34, 40, 41, 43).
The CK-PCr system can be considered nonessential at low workloads because of its reserve capacity, but its
importance increases with power output. Furthermore, although both functions operate at the same time, one might
prevail over the other, depending on metabolic demands. For example, its energy buffering role is more prominent in
Type II FT fibers; whereas its transport/ distribution role is more pronounced in Type I ST as well as cardiac tissue
(30–34, 40, 41, 43).
This system's efficiency, flexibility, and responsiveness provide functional advantages over one based
exclusively on ATP and ADP. It enables much higher power output than would otherwise be possible (on the order of
a 100-fold increase in muscular energy flux, corresponding to a 40-fold systemic increase) and also accelerates and
smooths the transition between workloads (2, 3, 30–34, 40, 41, 43). As part of the CK-PCr pathway, the PCr circuit
constitutes a sophisticated intracellular regulatory network with additional fringe benefits (30–34, 40, 41, 43):
•
By keeping [ADP] low, mitochondrial function is up-regulated.
•
ATPase inhibition is prevented, as is the net loss of adenine nucleotides.
•
Acidification is buffered during high workloads (at least initially, until PCr is depleted).
•
Glycogenolysis-glycolysis is indirectly stimulated.
“Creatine Trigger” Theory
The PCr circuit seems to be a rare example of a complex biologic system with simple kinetics. The first-order
exponential VO2 on-response indicates that there is one rate-limiting reaction in the involved pathways, and CK is the
likely candidate (8, 24, 25, 42). Furthermore, tissue VO2 appears to change in parallel with Cr, leading several
research groups to theorize that cellular metabolic activity is triggered by fluctuations in [Cr] and [PCr] rather than
[ATP], [ADP], and Pi or the ratios between them (as proposed in classic kinetic and equilibrium control models,
respectively) (8, 24, 25, 29, 32, 34, 35, 42).
Proponents of this Cr control model contend, quite convincingly, that it is the only viable explanation for
oxygen uptake kinetics as well as their proportionality with the [Cr]/[PCr] ratio (8, 24, 25, 29, 32, 34, 35, 42). If so,
this has profound physiologic implications: Indeed, it would indicate that other factors affecting cellular respiration
(pH, PCO2, PO2) and circulation (K+, Pi, H+) intervene only as modulators (8, 24, 25, 42). In any case, the CK-PCr
system appears to play a much more significant role in muscle metabolism than is apparent from the popular but
simplistic three-energy-system scheme.
Protein Synthesis
Cr stimulates myofibrillar protein synthesis, with its normal resting concentrations usually at the low end of the range
required to maximize this effect (possibly explaining why the process can be augmented by elevated tissue Cr) (4, 11,
18, 39). Likewise, Cr-depleted muscle demonstrates atrophic and other structural/metabolic changes (1, 2, 4, 11, 32,
38). Possible mechanisms for this include the following:
•
Loss of protein-bound Cr.
•
Reduced Cr-cofactor effect on myosin synthesis.
•
Impaired energy supply from the PCr circuit (i.e., for endergonic functions, such as protein synthesis,
contraction, ion transport, and amino acid uptake).
Consistent with these hypotheses is the possibility that increased tissue [Cr] might stimulate GTP production,
which in turn is required to initiate protein synthesis (35) . Alternatively, it has been proposed that the cellular
swelling (or so-called volumizing) effect resulting from Cr's osmotic activity might partially explain the mechanism
by which various hormones and amino acids regulate metabolic control, and in turn modulate anabolic activity, via
hydration status (20, 21, 38). In any case, it appears likely that optimal but as yet undetermined tissue [Cr] is needed
to maximize its biosynthetic action. Further research is needed to clarify this issue.
227
Summary
The PCr circuit is a feature of the CK-PCr system that allows it to serve a dual role: It is an energy capacitor as well as
a conduit through which cellular energy flux is coordinated in muscle. This establishes the theoretical groundwork for
up-regulating its function through combined training and nutritional strategies.
Ergogenic Effects
Cr supplementation can be viewed as a means of loading intramuscular Cr and PCr in a manner similar to
carbohydrate loading. Based on the central role of the CK-PCr system during high-power output, Cr loading could
theoretically improve the ability to produce energy-thereby increasing work capacity-for intense activity and the
subsequent rate of recovery.
As can be seen in this article's references section, considerable research has addressed the function of the
CK-PCr system and the effects of Cr supplementation on energy production and exercise performance. In fact,
carbohydrate is the only ergogenic nutrient that has been studied more extensively (about 80 original
research articles on Cr supplementation have been published in peer-reviewed journals as of this writing, and another
70 or so have been presented at various scientific meetings) (20, 21).
Collectively, the scientific literature indicates that short-term Cr loading (15–30 g/d, or 0.3 g/kg/d for 5–7
days) increases tissue [Cr] and [PCr] by 15–30% and 10–40%, respectively (1, 10–13, 16, 19, 20, 21, 26, 28, 38). It is
interesting to note that the upper storage limit is thought to be 150 to 160 mmol/kg dry
muscle and that few training studies demonstrated increases in tissue Cr and PCr deposition until creatine
monohydrate supplementation arrived on the scene. In any case, the greatest uptake has been shown to occur during
an initial 3- to 5-day loading phase, with elevated [Cr] and [PCr] maintained thereafter by ingesting 2 to 5 g/d (20,
21). Several research groups have observed that these levels return to baseline 4 to 5 weeks after cessation of
supplementation (Febbraio et al., Acta Physiol. Scand. 155:387–395, 1995; Lemon et al., Med. Sci. Sports Exerc.
27:S204, 1995; Vanderberghe et al., J. Appl. Physiol. 83:2055–2063, 1997).
Performance
Cr supplementation appears to enhance the rates of ATP and PCr resynthesis following intense exercise (1, 10–13, 16,
19, 20, 21, 26, 38). Although it does not seem to affect pre-exercise [ATP], the elevated [Cr] and [PCr] maintains ATP
to a greater degree during activities of maximal or near-maximal effort (20, 21). Most (70–80%) studies investigating
the ergogenic value of short-term (1 week) or long-term (20 week) Cr supplementation (20–25 g/d for 5–7 days and
2–25 g/d thereafter) report significant increases in strength, power, single and repetitive sprint performance, and work
performed during multiple high-intensity efforts (1, 10–13, 16, 19–21, 26, 28, 38). The higher the athlete's initial
tissue [Cr] and [PCr], the less dramatic the performance effects of short-term supplementation appear to be.
Short-term Cr supplementation seems to have no significant effect on submaximal endurance performance (1,
10–13, 16, 19, 20, 21, 26, 28, 38). Although no long-term studies have as yet addressed this issue, there might be
some potential benefits for endurance activities that warrant additional research. Because Cr supplementation has been
reported to enhance repetitive sprint performance, muscle mass, and glycogen uptake when ingested with large
amounts of carbohydrates (20, 21), it is tenable that endurance athletes could benefit from Cr supplementation by
virtue of improved interval training quality, muscle mass retention, and/ or muscle glycogen loading (reloading).
Additionally, Cr supplementation has been shown to improve training tolerance, with possible effects on endurance
performance capacity and/or likelihood of overtraining (20, 21).
Some well-controlled studies have reported no ergogenic benefits from Cr supplementation (1, 10–13, 16,
19–21, 26, 28, 38). The reasons for this are unclear, but possibilities include individual variability in response to
supplementation and differences in experimental design. Other potential limitations are as follows (20, 21):
•
Low (2–3 g/d) dosages without initial high-dose loading, or dosages <20 g/d for 5 days, appear to be less
ergogenic than those with longer- and/or higher-dosage protocols.
•
Studies using small sample sizes (e.g., <6 subjects/group) or crossover experimental designs with
<5-week washout periods between trials typically exhibit no ergogenic benefit.
•
Cr's ergogenic effect can also vary, depending on the amount of work performed and rest/recovery
allowed between repetitive work bouts.
•
Cr supplementation seems to have no effect on repetitive (60 seconds) sprint performance when
prolonged (5–25 minutes) recovery is allowed.
228
•
As previously mentioned, short-term Cr supplementation does not enhance submaximal endurance
performance.
Thus, although many Cr supplementation studies have demonstrated ergogenic effects (especially in
high-intensity and/or brief recovery situations), there are several notable exceptions.
Body Composition
Short-term Cr supplementation (20–25 g/d for 5–7 days) tends to increase total body mass by approximately 0.7–1.6
kg during resistance training (1, 10–13, 16, 19, 20, 21, 26, 28, 38). In addition, a number of long-term (20 week)
studies report significantly greater gains in fat-free as well as total body mass (20, 21). Depending on the length and
amount of supplementation, such gains tend to be 0.8 to 3.0 kg greater than those observed in matched-paired
controls.
Collectively, the existing research provides convincing evidence that Cr supplementation augments muscle
hypertrophy during strength/power training (1, 4, 9–13, 16, 17, 19–21, 26, 38, 39). There are three prevailing theories
about the underlying mechanism of this effect (20, 21).
Fluid Retention.. Long-term Cr supplementation increases total body water in proportion to weight gain (i.e.,
total body water might increase, but percentage total body water does not significantly change). Although initial gains
in body mass can be explained to some degree by fluid, the magnitude of change in muscle mass during chronic Cr
supplementation and training (e.g., mean changes up to 5.5 kg over 6 weeks) argues against this theory. This is
especially true when one considers the accompanying improvements in strength, power, and/or sprint capacity.
Protein Synthesis.. As previously mentioned, this theory suggests that anabolic/catabolic activity during
training is stimulated by the osmotic effect of Cr-induced intracellular water retention (especially during the initial
loading phase). In effect, this might indicate an autoregulatory mechanism whereby the cell maintains equilibrium
between its wet and dry constituents.
Improved Training Quality, in Turn, Providing a More Potent Adaptive Stimulus.. This is an attractive theory
that might explain results from long-term studies. However, it should be noted that significant increases in lean mass
have been demonstrated in as little as 1 week of Cr supplementation.
Each of these theories has supporting evidence, and none is mutually exclusive. Thus, it might be that a
combination of them best explains Cr's hypertrophic effect. More research is needed to clarify this issue.
By virtue of increasing lean body mass (as an end in itself or a means of improving strength and power), Cr's
indirect thermogenic effect is also worth consideration. Fats generally are not believed to be the preferred fuel during
such high-intensity activities (6), but one of the potential advantages of gaining lean tissue is an increase in basal
metabolism. All things being equal, the greater the athlete's muscle mass, the more calories he or she burns around the
clock. A fringe benefit of Cr-augmented hypertrophy is that it can be achieved without the concomitant body fat
deposition associated with hypercaloric diets. Although this is an intuitive suggestion that needs further research, it is
tenable that Cr supplementation can play a valuable role in body fat control/reduction when combined with sound
training.
Summary
The scientific community seems to be unified on two points regarding Cr supplementation. First, it works under
certain training/performance conditions. Second, ongoing studies are needed to better understand its mechanism(s) of
action as well as to continue evaluating its medical uses and safety (discussed below).
Clinical Effects
PCr Administration
Because of ionic properties that tend to stabilize cellular membranes and prevent ischemic/hypoxic damage-as well as
enzyme and nucleotide loss-intravenous or intramuscular PCr administration is used medically (8–12, 20, 21, 30):
•
As an antiarrhythmic agent and in the treatment of ischemic heart disease and myocardial infarction.
•
As a cardioplegic/cardioprotective agent (e.g., during heart surgery).
•
To prevent postsurgical lean mass wasting.
229
Because dietary creatine monohydrate supplementation increases the tissue [Cr] as well as [PCr] pools-and
heavy (especially eccentric) training is notorious for causing muscle cell disruption (6), albeit through a different
mechanism than that associated with myocardial pathology-it is possible that some indirect benefit might be achieved
by scheduling its intake in concert with recovery periods involving the greatest adaptive tissue remodeling (as
proposed in the Practical Issues and Guidelines discussion). Accordingly, it is interesting that Eastern European
coaches and sport scientists claim to have been administering Cr to athletes, mainly as a means of recovery, since the
1960s.
Cr Administration
Dietary Cr administration is used in treating mitochondrial cytopathies, and inborn Cr synthesis errors in infants (20,
21). Kreider et al. (Med. Sci. Sports Exerc. 30(1):73–82, 1998) and Earnest et al. (Clin. Sci. 91:113–118, 1996) have
also demonstrated that Cr ingestion can positively affect blood lipid profiles in trained athletes and hypertriglyceremic
subjects, respectively. Further research is needed, but these findings suggest that Cr supplementation might have
potential health benefits.
Possible Side Effects
Attention to this issue is growing at a fever pitch, and on one hand the concern is understandable. Indeed, how can
something that is purported to work so well not have a downside? Although many health-related concerns are being
reported anecdotally in the popular media, they are also being expressed by respected members of the sports medicine
community and thereby warrant further investigation. In any case, it should be kept in mind that clinical researchers
must report any unusual signs, symptoms, or adverse/ unexpected findings in their results. As of this writing,
however, increased lean body mass has been the only side effect reported in studies investigating Cr dosages up to 25
g/d for durations up to 1 year (4, 9, 10, 12, 13, 20, 21, 26, 28, 38, 39).
Fluid Retention/Weight Gain
Because Cr has been shown to modulate muscle protein synthesis (as previously mentioned), it is possible that the
osmotic effect that this would have on the cell accounts, at least in part, for the apparent fluid retention. However, it is
important to note that skeletal muscle is 70% water (6) . In light of the tightly regulated metabolic control strategies at
work, it is unlikely that one constituent would change in dissociation from the others, even during adaptive
hypertrophy. By comparison, it is interesting that intracellular glycogen is bound with water (via a different
mechanism) (6) and that glucose and Cr uptake are both modulated by insulin (1, 9, 10, 20, 21, 38, 39). However,
there does not seem to be the same concern regarding carbohydrate-loading techniques as is the case with Cr.
Muscle Cramps/Pulls
There are anecdotal claims that athletes training in hot and/or humid conditions might have a greater incidence of
severe muscle cramps and/or injuries when taking Cr. However, no Cr supplementation studies, including those
evaluating highly trained athletes undergoing intense training in such environments, report cramping, dehydration,
changes in electrolyte concentrations, or increased susceptibility to muscle strains or pulls (20, 21).
Our current research indicates that Cr users taking 8.3 g/d experienced less incidence of muscle cramps,
strains, or pulls than nonusers during triple-session preseason football camp in intense heat (these data are currently
unpublished but are being prepared as an ACSM abstract). Furthermore, the NCAA is presently funding several
research groups addressing the physiologic effects of Cr supplementation in collegiate athletes (these studies are
scheduled for completion in late 1999). Thus, more information on this issue is forthcoming.
Following is a working hypothesis that might account for the emerging perception of a causal effect between
Cr intake and muscle problems. The hydration and cramping issues have arisen mainly in American football. The
scene is not ubiquitous, but it is still too familiar: Athletes who pay the price in terms of off-season training and
nutrition report to preseason camp, only to encounter a coach who is determined to run them into shape for
consecutive days or weeks in full pads and summer heat. Football is a tough sport, and athletes must practice the way
they are going to play. Let us step back and think about this: By virtue of sound training and Cr supplementation, an
athlete is capable of generating greater heat, acid-base disturbances, dehydration, electrolyte washout, and substrate
230
depletion problems. Even in a well-fed and trained state, excessive work demands can do more to wear athletes down
than can be done to prevent or treat it.
Even the most effective and aggressive means of recovery or restoration cannot replete fuels, fluids,
electrolytes, and overall homeostasis if unrealistic workloads are inflicted over successive days (or weeks) in extreme
environmental conditions. It follows that significant metabolic problems and/or muscle dysfunctions can arise, and in
fact such athletes might be lucky if cramps or strains are the only negative result.
Adverse/Long-Term Health Effects
Concerns about possible long-term health problems are usually centered on sites of endogenous Cr production and/or
clearance as well as down-regulation of tissue uptake transporters. On the one hand, it seems unlikely that such
chronic problems would arise without forewarning from some type of clinical marker(s). The existing research on
acute hematological, hepatic, and renal responses to Cr supplementation is limited but does not indicate any problems
(1, 9, 10, 20, 21). Furthermore, as was previously mentioned, some potential health benefits might even exist.
Intense exercise—and certain disease states such as muscle degeneration and/or liver damage-can increase
serum CK (creatine kinase) and LDH (lactate dehydrogenase) levels as well as liver enzyme efflux. Cr
supplementation has little or no effect on liver ALT (alanine amino transferase), AST (aspartate amino
transferase), or GGT (gamma glutamyl transferase) efflux but might slightly elevate muscle CK and LDH efflux (20,
21). However, these values are well within normal limits for athletes engaged in heavy training and might simply
reflect higher CK activity and/or ability to tolerate greater training workloads. This is consistent with the fact that Cr
supplementation in the absence of training does not appear to influence serum muscle enzyme efflux (20, 21).
In terms of biosynthesis, Cr is produced via two sequential reactions which are suppressed (via feedback
inhibition from elevated plasma [Cr]) during periods of high intake (1, 2, 9–13, 17, 26, 38, 39). Although these
pathways are readily reactivated when supplementation is discontinued (1, 2, 11–13, 39), this finding, as well as
possible tissue transporter down-regulation, would seem to justify the use of cycling strategies that periodically clear
Cr from the blood (in turn promoting high biosynthetic/transport activity). Some hypothetical dosage distribution
tactics will be proposed in the Practical Issues and Guidelines discussion, but more research is needed to establish
optimal strategies.
In terms of excretion by the kidney, Cr is nonenzymatically degraded to creatinine and filtered from the
bloodstream via passive diffusion (neither of which is an energy-dependent step) (2, 12, 13, 16, 38). It seems unlikely
that the intake levels reported in the literature (i.e., <1 oz daily) would be problematic for healthy individuals. To date,
the only published study examining the effects of Cr loading on renal function supports this hypothesis: Poortmans et
al. (Eur. J. Appl. Physiol. 76:566–567, 1997) observed that arterial creatinine content, glomerular filtration rates
(indicative of creatinine clearance), and total protein and albumin excretion rates remained within normal ranges
despite a 3.7-fold increase in plasma Cr levels following supplementation (20 g/d for 5 days). Interestingly, 60% of
the ingested Cr was excreted without being converted to creatinine, with the kidneys reacting normally to elevated
levels. These researchers hypothesized that short-term Cr feeding has no detrimental effect on kidney function in
healthy subjects.
Summary
Serum and urinary Cr increase for several hours after Cr ingestion. During training, there might be an increase in
serum creatinine and muscle enzyme efflux. These changes appear to be related to excess Cr excretion and/or greater
training intensity (with a subsequent increase in net protein degradation). There might also be some positive effects on
blood lipid profiles. In the absence of training, there appears to be little or no effect on serum and urinary creatinine,
muscle and liver enzymes, or blood pressure. This provides some indirect evidence that the elevated creatinine is
related to greater training workload rather than some sort of pathology. Although additional research is necessary to
evaluate long-term effects on medical status, the existing scientific literature suggests that up to 2 years of PCr or Cr
administration is medically safe. No side effects (other than weight gain) have been documented in numerous studies,
and in fact there might be specific health benefits for certain populations.
231
Practical Issues and Guidelines
The strength and conditioning scene is replete with training methods or techniques for which inherent benefits and
risks are a function of the dosage more so than the medicine itself. For the purposes of this discussion, the acquisition
and skillful application of quality Cr products might be the central issues.
A Buyer's Market?
Because creatine monohydrate arrived on the U.S. market in the early 1990s, a growing number of vendors have been
targeting various athletic programs in an effort to build their customer list. The situation is compounded by the fact
that the market is being flooded with low-quality product of overseas origin and possibly with domestic product
which is being cut by unscrupulous distributors or importers (often accompanied by a bogus/photocopied certificate of
analysis or none at all). As prices continue to drop, the key when making a purchase is to establish the vendor's
credibility as well as the source and quality of the product.
Although this seems like a no-brainer, unfortunately the adages “read the label” and “buyer beware” are
inadequate. The importance of quality control can be appreciated when considering how synthetic creatine
monohydrate is manufactured from its raw materials (cyanamide, sarcosine, and water). Cyanamide is very irritating,
caustic, and acutely toxic when ingested (7) and could be hazardous if present in the final product because of inferior
manufacturing processes. In any case, because there is no way to know precisely how serious the counterfeit/impure
Cr problem has become, it is advisable to use discretion in selecting a product.
Quality Assurance
It is possible to hold a vendor's feet to the fire and acquire high-quality Cr products by requiring the following
documentation:
1. The product should be manufactured in a USFDA-inspected facility complying with pharmaceutical
“Current Good Manufacturing Practices” (the code of federal regulations describing methods, equipment, facilities,
and controls used for manufacturing, processing, packing, or holding drugs and foods) (36) . This also means that it
should comply with “Manufacturing Practices for Nutritional Supplements” cited in the following (37) :
•
U.S. Pharmacopeia 23 (standards for purity, quality, and strength)/National Formulary 18 (standards for
packaging, labeling, and storage).
•
Selected portions of the Federal Food, Drug & Cosmetic Act related to dietary supplements
2. A manufacturer's (not distributor's or importer's) certificate of analysis should be provided for random
samples from the same batch/lot number on the containers being purchased. Different laboratories might not test for
each physical constant listed below, and typical values might vary slightly (thus none are indicated here). However,
the vendor takes a big step toward establishing credibility simply by providing this type of documentation:
•
Appearance (white to pale cream solid).
•
Assay (determined with HPCE or HPLC methods).
•
Bulk density.
•
Mesh size.
•
Microbiological/pathogenic contamination (e.g., coliforms, E. coli, salmonella, Staph. aureus,
yeasts/molds), and plate count.
•
Poisons (e.g., arsenic) and heavy metals (e.g., lead, mercury).
•
Residual moisture/loss on drying.
•
Residue on ignition (for inorganic materials).
Reputable manufacturers who adhere to these industry standards typically do not hesitate to share this
information with potential distributors or vendors. Indeed, it would be foolish to invest the effort and money involved
in such quality control/assurance measures without advertising it. Information is power when it is acted on, so hold
them accountable for providing it, and walk away or hang up if they claim that it is not available!
Supplementation Suggestions
The decision of whether to use any food supplement (and how to do so) is ultimately a matter of personal discretion.
The following suggestions are intended to illustrate a selective “rifle” approach to Cr supplementation with respect to
a few precepts.
232
Depending on lean mass, an athlete's musculature can usually be Cr saturated via a 5-day loading phase
consisting of three or four daily servings of 5 g each, or about a teaspoonful at a time (equivalent to that contained in
1 kg of lean, raw meat, so a little goes a long way) (1, 9–12, 16, 19–21, 26, 38). Furthermore, elevated [Cr] is retained
for several weeks after supplementation lapses because leakage from the tissues occurs very slowly (i.e., at a 3% daily
turnover rate) (1, 9–12, 16, 19–21, 26, 38, 39). Thus, it might not be necessary to go on a set daily maintenance
dosage once saturation is achieved, and so, after tissue loading is completed, possible maintenance strategies might
include the following:
•
Ingesting Cr with meals to fully exploit the insulin uptake effect (38, 39).
•
Minimizing caffeine intake, which might counteract its ergogenic action (Vandenberghe et al., J. Appl.
Physiol. 80: 452–457, 1996).
•
Discontinuing Cr use during cessation of training.
•
Cycling Cr intake to coincide with the periods of greatest recovery/adaptation (as described below).
This last guideline is intuitive advice that is not currently supported by scientific research. Theoretically,
however, a zigzag approach can optimize Cr's benefits while minimizing accommodation problems. It is also
consistent with its membrane stabilization and intracellular retention properties, the negative-feedback effect of
elevated plasma [Cr], and the concept of integrating periodized training with nutritional supplementation.
Table 1 Hypothetical Daily Cr Servings With Respect to Body Mass
Table 1 is an example of how to apportion daily Cr servings with respect to body mass during 4 d/wk resistance
training consisting of structural lower-body exercises on Monday and Thursday and non-weight-bearing upper-body
exercises on Tuesday and Friday. This approach can obviously be adapted to different workout schedules. In this way,
Cr intake is scheduled to coincide with recovery from workloads involving the greatest muscle mass and most
profound training effects. Some alternative approaches might be the following:
•
Use Cr in conjunction only with heavy workouts, discontinuing its intake during the last half of each
week (comprised of explosive workouts with less of a structural training effect).
•
Use Cr during weeks/phases coinciding with the most intensive (or extensive) training, with regular cyclic
breaks from supplementation, depending on how the program is periodized.
•
Simply reduce the size of each Cr serving in conjunction with any of these tactics.
Summary and Conclusions
1. Cr participates in the CK-PCr system, which acts as a capacitor as well as a conduit for intramuscular
energy flux.
2.
•
•
Short-term Cr supplementation can improve the following:
Maximal strength/power (5–15%) and work performed during sets of maximal efforts (5–15%)
Single-effort sprint performance (1–5%), and work performed during repetitive sprints (5–15%)
3. Long-term Cr supplementation can promote significantly greater gains in strength, sprint performance,
and lean mass during training than in matched-paired controls.
4. Ergogenic benefits of Cr supplementation have not been found in all studies, possibly because of
differences in the following:
•
Individual subject response.
•
Dosage and/or duration of supplementation protocol.
•
Exercise criterion evaluated.
•
Recovery allowance between work bouts.
233
5. Based on existing scientific information, Cr administration appears to be a safe and effective nutritional
strategy to enhance high-intensity exercise performance and muscle hypertrophy. Weight gain is the only reported
side effect of Cr supplementation in studies lasting up to 2 years.
6. Cr products should be accompanied by documentation verifying the manufacturer's compliance with
certain industry standards for quality control and assurance.
7.
•
•
•
Ongoing research of Cr supplementation should address the following:
Mechanism of ergogenic action.
Clinical uses.
Dose-response relationships and cycling/distribution strategies during training.
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Steven Plisk is the Director of Sports Conditioning at Yale University. His previous experiences include the
University of Memphis, U.S. Olympic Training Center, James Madison University, Dartmouth College, Austin
Peay State University and the University of Colorado. He received his B.S. in Sport & Exercise Science from
SUNY-Buffalo in 1987 and his M.S. in Kinesiology from the University of Colorado in 1990, and is a Certified
Strength & Conditioning Specialist through the NSCA as well as a Level I coach through USA Weightlifting.
His current NSCA activities include the Strength & Conditioning Journal Review Board and Power Systems
Scholarship Selection Committee.
Richard B. Kreider, PhD, serves as Associate Professor, Assistant Department Chair, and Director of the
Exercise & Sport Nutrition Laboratory in the Department of Human Movement Sciences & Education at the
University of Memphis. Dr. Kreider has published more than 100 research articles /abstracts and has conducted
six studies on the safety and efficacy of creatine supplementation among athletes. Dr. Kreider serves as
Research Digest Editor for the International Journal of Sport Nutrition, serves on the editorial board of JSCR, is
a Fellow of the American College of Sport Medicine (ACSM), is ACSM certified as an Exercise Specialist and
Health/Fitness Director, and is an active member of the NSCA.
© Copyright by National Strength and Conditioning Association 1999
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The Newsletter of Athletic Performance
Vol. 3 No. 1 September 1994
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The Physician and Sports Medicine—February 1976
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PREGAME MEAL: TO EAT OR NOT TO EAT—AND WHAT?
The content of the pregame meal is usually based on tradition passed on from coach to coach, without much
consideration of its value to the players. The traditional precompetition meal--steak, scrambled eggs, green beans,
toast, honey, and tea--is still widely used today because most coaches are not aware that this is not wise for
physiological reasons. Rose and Fuenning1 at the University of Nebraska found that this type of meal was still in the
stomach after the game was over, and it could only have acted as an extra weight or bolus of no nutritional value to
many players.
There are several other types of precompetition meals. We think it is probably best for an athlete to eat an easily
digestible, high carbohydrate pregame meal if he feel he needs to eat at all. The protein dominated meal takes about
5% to 10% more oxygen to metabolize or even start to digest. In addition, the kidneys have to excrete the ammonium
acid and urea that is the waste product of protein metabolism, and any athlete worth his salt will be shunting the
majority of his blood away from the kidneys to the muscles. This means the waste products just circulate until after
the game and may contribute to more early signs of fatigue. The breakdown products of carbohydrate metabolism
end up as carbon dioxide, which can be excreted easily through the lungs. The kidneys aren't necessarily involved.
We recommend a precompetition meal of orange juice, pancakes with a small amount of butter and syrup, dry
toast, honey, fruit, fruit cup of Jell-O, milk or tea with sugar.2
Several years ago during a regular football season we studied the effect of a liquid pregame meal and found that
athletes experienced no nausea, vomiting, or stomach cramps, and that their stamina was not adversely affected.3
This regimen is still used by many schools and it certainly has merit. Many good athletes have no desire to eat, and
we agree that the pregame meal is not essential. In fact, we have observed over many years that some of the truly
great athletes ate absolutely nothing before competition.
We do agree with Astrand that the food consumption of the athlete should probably be somewhat modified before
competition. We think he should try to eat a diet with an increased amount of carbohydrates the day before
competition to improve his stamina for prolonged exercise. The pregame meal advocated by Astrand consists of
porridge, bread, eggs, butter, coffee, and milk.
In a study testing three different pregame meals (steak and eggs, pancakes, and oatmeal and eggs), no significant
difference was found in the athlete's performances in the two-mile run.
A questionnaire completed by the
participants suggested that the psychological factors surrounding the pregame meal may be more significant than the
food.5
We feel that the content of the pregame meal is not critical as long as it does not make the athlete sick,
uncomfortable, irritate his gastrointestinal tract, or markedly delay the emptying time of his stomach. Far more
important is the combination of diet and exercise during the week preceding competition. By working extremely hard
on Tuesday and Wednesday, thus exhausting the muscle glycogen; and having light workouts on Thursday, very little
or no work on Friday, and a diet higher in carbohydrate foods these latter two days, the athlete should be ready for
competition and a maximum effort on Saturday.
What the athlete eats as his pregame meal is probably not going to influence physiological performance a great
deal. But it may very well have an important psychological impact. The main thing is not to handicap the athlete's
chances for an optimum performance and not to worry if he prefers to eat nothing.
______________________________________
References
1. Rose KD, Fuenning SI: Pre-game Emotional Tension, Gastrointestinal Motility and the Feeding of Athletes. Neb Med J
45:575-579, 1960.
2. Cooper DL: Athlete's Diet Must Match His Sports' Caloric Demands. Medical Tribune, Oct, 1965.
3. Cooper DL, Bird B, Blair J: Use of a liquid meal in a football training program. J Okl State Med Assoc 55:484-486, 1962.
4. Astrand PO: Diet and Athletic Performance, Federation Nov, Dec, 1967.
5. Fair JD: Effects of Three Pre-Competition Meals Upon Subsequent Performance in a Two-Mile Run. M V Thesis. U North
Dakota, 1974.
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