Glutamine unlikely to boost athletic performance

NEW YORK (Reuters Health) - There is little evidence that supplements containing the amino acid glutamine can enhance athletes' performance, according to a research review.

Glutamine is a non-essential amino acid, which means that the body synthesizes its own supply. However, glutamine is also found in a range of foods -- from meat and cheese to yogurt and spinach -- and in dietary supplements marketed as performance enhancers, according to Dr. George C. Phillips of the University of Iowa Children's Hospital in Iowa City.

Amino acids are the building blocks for proteins in the body, and one of the functions of glutamine is to help produce energy. Research shows that a person's blood levels of glutamine decline after exercise, but that long-term training boosts athletes' resting glutamine levels.

Glutamine aids in the synthesis of white blood cells of the immune system, which theoretically could counter the drain on the immune system that can occur with intense training.

All of this suggests that increasing glutamine levels with supplements could enhance athletic performance, Phillips notes. However, studies have not borne this out, he writes in the journal Current Sports Medicine Reports.

Phillips looked at a number of studies that tested whether glutamine supplements can increase muscle strength, speed up post-workout recovery or prevent colds by boosting immune function in hard-training athletes.

There was no consistent evidence of any of these benefits. This, coupled with the fact that glutamine supplements may raise cholesterol, "calls into serious question the appropriateness of glutamine as a dietary supplement," he writes.

"Unfortunately," Phillips concludes, "this appears to be another example of commercial marketing trumping scientific evidence that in this case demonstrates how nonessential glutamine supplementation is to athletic performance."

SOURCE: Current Sports Medicine Reports, August 2007.