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Right Amount of Protein for Athletes
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The Right Amount of
Protein for Athletes
by Ed Burke, Ph.D.
Without proper dietary support,
metabolically stressful workouts and training regimens can result in more muscle
damage than development, as well as disappointing strength and endurance gains
It's common knowledge that athletes need more carbohydrates than the
average person. Less known is that athletes also need more proteins for the
muscle growth and tissue repair that accompanies the tough physical demands they
place on their bodies. Moreover, athletes need more amino acids—the building
blocks of protein—for the numerous metabolic pathways and processes involved
in exercise. Some amino acids, for example, influence hormone production and
neurotransmission, physiological processes thought to influence athletic fatigue
and performance.1
Basically, athletes need more protein than the average person because their
workouts are more metabolically stressful. During periods of great physical
exertion, the body steps up its use of the Amino
Acids and proteins essential for oxidative energy production. If large
amounts of protein are broken down and not replaced, athletes will go into a
negative amino acid balance. They'll also be unable to compensate for the
nitrogen their bodies lose during hard workouts. (Nitrogen is a byproduct of
protein breakdown.) This, in turn, may have a negative effect on amino acid
synthesis. Bodybuilders and other weight-conscious athletes such as wrestlers,
dancers, gymnasts and female long-distance runners are most likely to be
affected. Under certain circumstances, vegetarian athletes may also be at risk.
Athletes'
Protein
requirements increase during training. According to current knowledge, training
amounts are approximately 1.2 to 2.0 grams of protein per kilogram of body
weight per day for adults,2 compared to the Recommended Dietary
Allowance (RDA) of 0.8 gram/kg. for non training adults. Assuming sufficient
total caloric intake, this desired amount is likely to be present in any mixed
diet that contains 12 percent to 15 percent of its energy as protein.
Interestingly, this value is consistent with most current macronutrient
recommendations for athletes—a diet that is 60 percent to 70 percent
carbohydrates, 12 percent to 15 percent protein and less than 30 percent fat.
Although it is frequently said that high-protein diets may cause liver or kidney
disorders, the possibility is not well documented and isn't a concern at these
modest protein intake levels.3
Although the protein intake of many athletes—especially strength athletes and
bodybuilders—substantially exceeds the RDA, many scientists erroneously
consider these large quantities of dietary protein to be of little value.4
The protein RDA is only a broad-population guideline, however, and is based on
data from relatively sedentary individuals.5 Recent studies using
athletic subjects suggest that protein intake greater than RDAs is appropriate
for some kinds of athletes.
Two decades ago, researchers demonstrated that a protein intake of 1.0 gram/kg.
of body weight per day was sufficient to meet the needs of sedentary subjects.
However, despite adequate total energy intake, this amount of protein was
insufficient when these same subjects began an endurance (cycling) training
program.6 Some reports on moderate exercise training suggest that the
increased protein needs last only a few weeks at the beginning of an exercise
program;7 but two recent studies involving more intense endurance
exercise demonstrated increased protein requirements in individuals who had been
training for several years.8,9
Perhaps both novice and experienced endurance athletes benefit from dietary
protein in excess of the current RDA, but for different reasons. Novice athletes
need protein to minimize loss of blood proteins, whereas conditioned athletes
need it to provide amino acids for exercise fuel or muscle repair.10
If food energy intake isn't enough to support increased energy expenditure
during training, or if food intake is restricted for weight loss, protein needs
may increase.11 Under any of these circumstances, athletes consuming
only 100 percent of the RDA for protein may experience decreases in muscle mass
and strength.
Endurance Exercise And Protein
Needs
Endurance exercise requires greater amounts of several amino acids as exercise
fuel (especially the branched-chain amino acids such as leucine, isoleucine and
valine).12 High exercise intensity, long periods of exertion,
decreased carbohydrate availability and even stresses related to the exercise
environment appear to promote greater amino acid oxidation.13 Such
factors could alter rates of protein synthesis or breakdown and lead to an
elevated dietary protein requirement of 1.2 to 1.4 grams/kg. of body weight per
day.
Muscle damage occurs during endurance exercise, especially if it includes an
eccentric component such as muscle tension that results from running downhill.14
Additional dietary protein might help repair these damaged muscle cells.
Strength Exercise And Protein
Needs
It is well known that carbohydrates are very important for athletes who train
extensively with weights. These athletes need to eat enough dietary
carbohydrates to provide energy for their high-intensity exercises. In contrast,
since strength training consists of short bouts of extremely intense effort, it
would seem unlikely that amino acid oxidation is an important source of energy
for such exercise. However, some published results suggest that additional
dietary protein can also enhance strength gains.
Five of 10 elite weight lifters studied by Polish scientists were found by
nitrogen balance methods to be consuming inadequate protein even when their
protein intake was 2.0 grams/kg. of body weight per day.15
Unfortunately, one of these five athletes consumed a diet containing inadequate
total calories. Because insufficient food intake elevates protein needs, the
data from this individual are difficult to interpret. However, even when this
subject is excluded, four of the 10 weight lifters had protein needs exceeding
2.0 grams/kg. of body weight per day.
In another study, five subjects whose diets consisted of 0.8 gram/kg. of body
weight per day of protein and whose total calorie intake was adequate
experienced a decreased cell mass (measured by potassium-40) over six weeks of
strength training.16 With continued training and an increase in
protein intake to 1.6 grams/kg. of body weight per day, their cell mass
increased.
A study of nitrogen balance in bodybuilders demonstrated increased protein needs
relative to controls and estimated the RDA for bodybuilders to be about 0.9
gram/kg. of body weight per day.17
Finally, impressive strength gains of 5 percent and size gains of 6 percent in
world-class weight lifters were observed over several months of strength
training when the athletes increased their dietary Protein
from 1.8 grams/kg. to 3.5 grams/kg. of body weight per day.18
Compared to the protein intakes of most strength athletes, the protein levels
that produced gains in muscle strength and size in the world-class weight
lifters19 are greater than those suggested by most studies that use
the nitrogen-balance technique.20 This may mean that although a
positive nitrogen balance can be maintained during a strength-training program
with a protein intake equal to or slightly above the RDA, higher intakes are
necessary for optimal gains in muscle size and strength. Preliminary evidence
for this exists in a study that found greater nitrogen retention (estimated from
dietary nitrogen minus urinary nitrogen) and greater gains in lean body (muscle)
mass during four weeks of strength training when subjects consumed 2.4 grams of
protein per kg. body weight per day compared to 0.8 gram of protein per kilogram
body weight per day.21
Together, the studies suggest that a protein intake in excess of the RDA will
enhance the muscle strength and size gains induced by a strength program. Such a
conclusion is somewhat speculative, however. Most of the studies use indirect or
incomplete measurements and few subjects. Future studies with larger sample
sizes and more direct measures are needed to confirm the observations.
People attempting to increase muscle strength and size through strength training
might try consuming the equivalent of 1.2 to 2.0 grams protein to kilogram body
weight per day (about 150-250 percent of the current protein RDA for adults).
Sources of Dietary Protein
In general, athletes' use of protein supplements during training is established
and continually fostered. Luke Bucci, Ph.D., in his book, Nutrients As
Ergogenic Aids For Sports and Exercise, says that protein powders are a more
cost-effective source of protein per dollar than vegetables, grains, nuts,
cheeses, fish and most beef products. Protein powders are less cost-effective,
however, than powdered milk, eggs, chicken or pork.22
Except for nonfat powdered milk, foods that are less costly than protein powders
generally contain considerable quantities of fat and excess calories that
athletes such as bodybuilders are trying to avoid. For the cost of a nice dinner
out or a one-week supply of meat, athletes can buy a month's worth of
Protein
Powder—approximately 50 grams per day of supplemental protein. That's why
many athletes view protein powders as a cost-effective and convenient sources of
additional dietary protein. For these reasons alone, protein supplements will
remain in demand.
Two other forms of protein supplementation have recently hit the market23—protein
hydrolysates and free-form amino acid mixtures. Hydrolysates are the single
amino acids, dipeptides and tripeptides, that are made by putting intact
proteins into either an enzyme or acid bath and breaking them apart. Enzymatic
hydrolysis retains the serine, threonine, tryptophan, cysteine and salts that
are often lost during acid hydrolysis.
An ever-increasing number of hydrolysates are commercially available. Despite
the lack of evidence, some companies claim their products improve or hasten
absorption better than dietary proteins or even amino acid mixtures do. However,
such protein hydrolysate products are two to five times more expensive than
protein powders containing the same amount of nitrogenous material.
Amino acid mixtures have lately gained in popularity now that large amounts of
food-grade L-amino acids are readily available. Most free-form amino acids are
produced in Japan by microbial fermentation. That's why relying on free-form
amino acids as a sole dietary nitrogen source gets expensive.24
Proponents of free-form amino acid mixtures claim that absorption is complete
and the mixtures are totally digested. They also claim that absorption of
nitrogen is more rapid than from proteins and that amino acid compositions can
be manipulated to optimize energy or protein synthesis for athletes. Various
physiological parameters such as hormone release are also purported to be
influenced. However, more research is needed to support the claims of
manufacturers of free-form amino acid mixtures.
Other inconclusive data suggest that individual amino acid supplementation may
benefit some types of exercise performance. Branched-chain amino acids,
tryptophan, glutamate, aspartate and potential growth hormone-stimulating amino
acids are among the amino acids being investigated.25 This is an area
where additional research is needed because very few studies have documented
actual performance-enhancing effects.
Summary
It is safe to say that serious athletes require protein levels that exceed the
RDA. Although definitive dietary recommendations for various athlete groups must
await future study, much current evidence suggests that strength athletes and
bodybuilders should consume up to 2.0 grams/kg. of body weight per day (250
percent of RDA) and endurance athletes up to 1.4 grams/kg. of body weight per
day (175 percent of RDA). These quantities can be obtained from a diet that
consists of 12 percent to 15 percent energy from protein, unless total dietary
energy intake is insufficient. It should be noted, however, that too much of an
increase in dietary protein over the long run may have some detrimental effects.
Such a program should be overseen by a physician.
References
1. Lemon, P.W.R. "Effect of exercise on protein requirements," Journal
of Sports Sciences, 9: 53-70, 1991.
2. Brouns, F. Nutritional Needs of Athletes: 37-47.
New York: John Wiley & Sons, 1993.
3. Durnin, J.V.G.A. "Protein requirements and physical
activity," In V.A. Parizkova, & D.D. Rogozkin, eds., Nutrition,
Physical Fitness and Health: 53-63. Baltimore, Md.: University Park Press,
1978.
4. Shils, M.E., & Young, V.R. Modern Nutrition in
Health and Disease: 147-153. Philadelphia, Pa.: Lea & Febiger, 1988.
5. U.S. Food and Nutrition Board. Recommended Dietary
Allowances: 52-77. Washington, D.C.: National Academy of Sciences, 1989.
6. Gontzea, I., Sutzescu, P., et al. "The influence of
muscular activity on nitrogen balance and on the need of man for protein," Nutrition
Reports International, 10: 35-43, 1974.
7. Butterfield, G.E. "Whole-body protein utilization in
humans," Medicine and Science in Sports and Exercise, 19 (no. 5
suppl.): S157-S165, 1987.
8. Friedman, J.E., & Lemon, P.W.R. "Effect of
chronic endurance exercise on retention of dietary protein," International
Journal of Sports Medicine, 10: 118-223, 1989.
9. Tarnopolsky, M.A., MacDougall, J.D., et al.
"Influence of protein intake and training status on nitrogen balance and
lean mass," Journal of Applied Physiology, 64: 187-193, 1988.
10. Lemon, P.W.R. "Nutrition for muscular development of
young athletes," In C.V. Gisolfi, & D.R. Lamb, eds., Perspectives in
Exercise Science and Sports Medicine, Vol 11, Youth, Exercise, and Sport:
2-3. Indianapolis, Ind.: Benchmark Press, 1989.
11. Goranzon, H., & Forsum, E. "Effect of reduced
energy intake versus increased physical activity on the outcome of nitrogen
balance experiments in man," American Journal of Clinical Nutrition,
41: 919-928, 1985.
12. Lemon, P.W.R., & Nagle, E.J., et al. "In vivo
leucine oxidation at rest and during two intensities of exercise," Journal
of Applied Physiology, 53: 947-954, 1982.
13. Lemon, P.W.R. "Protein and exercise: update
1987," Medicine and Science in Sports and Exercise, 19 (no. 5 suppl.):
S179-S190, 1987.
14. Armstrong, R.B., Ogilvie, R.W., et al. "Eccentric
exercise-induced injury to skeletal muscle," Journal of Applied
Physiology, 54: 80-93. 1983.
15. Celejowa, I., & Homa, M. "Food intake, nitrogen
and energy balance in Polish weight lifters during a training camp," Nutrition
and Metabolism, 12: 259-274, 1970.
16. Torun, B., Scrimshaw. N.S., et al. "Effect of
isometric exercises on body potassium and dietary protein requirements of young
men," American Journal of Clinical Nutrition, 30: 1983-93, 1977.
17. Tarnopolsky and MacDougall, loc. cit.
18. Hi Dragan, G.L., Vasiliu, V., et al. "Effect of
increased supply of protein on elite weight lifters," In T. E. Galesloot.
& B.J. Tinbergen, eds. Milk Proteins: 99-103. Wageningen, The
Netherlands: Pudoc, 1985.
19. Dragan and Vasiliu, loc. cit.
20. Tarnopolsky and MacDougall, loc. cit.
21. Marable, N.L., Hickson, J.F. et al. "Urinary
nitrogen excretion as influenced by a muscle-building exercise program and
protein intake variation," Nutritional Reports International, 19:
795-805, 1979.
22. Bucci. L. Nutrients as Ergogenic Aids for Sports and
Exercise: 14-18. Boca Raton, Fla.: CRC Press, 1993.
23. Bucci, loc. cit.
24. Bucci, loc. cit.
25. Lemon, P.W.R. "Do athletes need more dietary protein
and amino acids?" International Journal of Sports Nutrition, 5:
S39-S61, 1995.
Edmund R. Burke, Ph.D., is an associate
professor of biology at the University of Colorado, Colorado Springs, as well as
a lecturer and co-author of Training Nutrition. Burke also serves as
director of sports sciences for the U.S. Cycling Team.
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