Essentials of Nutrition for Sports

Amino acid supplements may interfere with synthesis of body
protein by creating imbalances. Amino acids compete for absorption; large quantities of free amino acids at the intestinal mucosal surface reduce the amount that can be abso

rbed from the available supply.

A large US nutritional retailer was fined $2.4 million by the

Federal Trade Commission for promoting free-form amino acids as a stimulator of growth hormone production.

There is little evidence that any amino acids or biochemical

enzyme supplements have any valu

e. Here is a brief summary of

some amino acids studies of the last decade:

Amino acid supplement

was found to reduce some hormonal

changes associated with overtraini

ng in a study sponsored by the

manufacturer.

Amino-Vital

, a proprietary product, was shown to have mixed

performance effect in 30 female college students. These students were fed 30 minutes before exercise with branched chain amino acids. Unfortunately, the placebo group received no calories. After three months of steady supplementation, no effect on aerobic capacity was found.

Arginine

in a dose of 5 grams increased growth hormone levels.

Branched-chain amino acids

are purported to be a fuel source, to

decrease tryptophan uptake by the brain, to change serotonin levels in the brain, or to improve immunity. The brain hormone level changes are supposed to reduce exercise fatigue. Roughly 1 study out of 10 has found marginal benefit.

Citrulline malate:

This is an amino acid found in watermelon

and milk protein. Improved aerobic capacity was found in one study.

Leucine

supplementation: No effect on performance.

Methionine:

No change in strength was found in 21 well-trained

weight lifters.

Tyrosine

, an amino acid and dopamine precursor, added to

carbohydrate was found not to improve cycling performance.

Bottom Line

Review the key points. Aim for good quality protein intake up to a maximum of 20% of

calories or 1.5 grams of protein per kilogram (0.7 grams per pound).

Nutrition for Sports, Essentials of 64