Brached Chain Amino Acids for Exercise Performance
Today’s Dietitian
By Leslie K. Kay, MS, RD
Vol. 6 No. 5 p. 48

May is National Physical Fitness and Sports Month, which is designed to increase awareness of the joy and benefits of an active lifestyle. Americans often complement their exercise regimen by consuming a dietary supplement promoted to enhance physical fitness. Approximately one out of 10 supplements sold belong to the sports nutrition category, totaling $1.8 billion annually in an $18 billion industry. Protein powders and pills are athletes’ supplements of choice, capturing the largest piece of the sports supplement pie.

Branched chain amino acids (BCAAs [isoleucine, leucine, and valine]) are promoted to enhance exercise performance, prevent fatigue, improve concentration, and reduce protein and muscle breakdown during intense exercise.
Claims:
• Improves exercise performance
• Increases stamina
• Builds muscle tissue
• Improves mental concentration

BCAAs are a group of essential amino acids that have been studied for their potential role in delaying central nervous system (CNS) fatigue, especially in athletes. The hypothesis is this: If exercise fatigue can be reduced or delayed, then physical performance would be improved as endurance would increase since the athletes’ perception of fatigue would be temporarily altered. Muscular fatigue can obviously prevent an exercise or training session from continuing, but so can the perception of fatigue, or so-called central fatigue.

If an athlete does not feel fatigue, exercise duration can be extended. Following ingestion, BCAAs are not readily broken down by the liver. They instead circulate and compete for absorption into the blood-brain barrier with the amino acids tryptophan, tyrosine, phenylalanine, and methionine for access to the neural amino acid transport system that allows amino acid entry to the brain.

Here’s how it works: Tryptophan is a precursor to serotonin (5-hydroxytryptamine, or 5-HT), which may depress the CNS and produce symptoms of fatigue. Research has shown that exercise increases the ratio of free tryptophan/BCAA, thus raising serotonin levels in the brain. Evidence also exists to show that plasma BCAA levels decline during endurance exercise. Some researchers speculate that supplementing with BCAAs will lower this ratio and result in improved mental and physical performance.

In a placebo-controlled (not blinded) study, 193 experienced runners were randomly assigned to drink 16 grams of BCAA in a 5% glucose beverage or a placebo during a 30- or 42.2-kilometer race. The running performance was improved for the “slower runners” (3.05 to 3.30 hours) when BCAAs were taken during the race. No improvement was seen in the faster runners (<3.05 hours).1 A second part of this study examined the effects of 7.5 grams BCAAs on mental performance during a 30-kilometer cross-country race. Mental performance measured after the race was improved in runners supplemented with BCAA. However, researchers have criticized this study for its choice of performance measures, lack of blinding the study, and lack of dietary control.2

In another study (double-blind, crossover design), seven endurance-trained male cyclists were given a 7-gram BCAA solution or a placebo before cycling for one hour at 70% maximal power output exercise followed by 20 minutes of maximal exercise. Every 10 minutes, subjects rated their perceived exertion and mental fatigue. While there was no difference in physical performance, the ratings of perceived exertion and mental fatigue were significantly lower with the BCAA group.3

SAFETY
There are mixed reviews regarding the safety of taking BCAA orally. It is probably safe when used appropriately and short term. BCAAs have not been associated with significant adverse effects in studies lasting from one to two weeks up to six months; however, side effects of supplementing with high doses of BCAA include an increase in plasma and muscle accumulation of ammonia, which itself can contribute to fatigue. Increased blood concentrations of ammonia can lead to a temporary loss of motor coordination and compromised muscle and brain function.

It is possible that large doses of BCAA (>20 grams) may impair water absorption across the gut and cause gastrointestinal discomfort. The long-term safety of ingesting large doses of “free-form” amino acids is not known. Other essential amino acids may be displaced when high doses of BCAA are administered.

Dietary use of BCAAs in alcoholics has been associated with hepatic encephalopathy.

ADDITIONAL USES FOR BCAAS

Diabetes
Some evidence suggests that BCAAs might stimulate insulin release and therefore, theoretically have an additive hypoglycemic effect with antidiabetic medications. Whether dietary supplementation of BCAAs can increase the efficacy of glucose-lowering medications or reduce dependency on insulin is unknown.

Anorexia
By decreasing the synthesis of serotonin, BCAAs might increase appetite. Supplementing with BCAAs (4 grams three times per day) has been shown to reduce anorexia and improve the overall nutritional status in older malnourished, hemodialysis patients. Preliminary evidence suggests that oral BCAAs might be helpful for anorexia in cancer patients.

SUMMARY
There is evidence that taking BCAAs orally seems to reduce muscle breakdown during exercise.4 If BCAA ingestion reduced the uptake of the amino acid tryptophan from the blood into the brain so that less tryptophan were converted to serotonin in the brain and if a buildup of serotonin in the brain caused early fatigue during exercise, a case could be made for consuming BCAA before and during exercise.

Studies published a few years ago suggested that BCAA supplements could delay fatigue during long-duration endurance exercise. However, these studies were not well-controlled, and several reports since then have not shown any effect of BCAA supplements on delaying fatigue under normal circumstances. There is some evidence that these supplements may work in extreme conditions such as high altitude, but, at best, it appears that ingestion of BCAA is not effective in improving exercise performance.

— Leslie K. Kay, MS, RD, has worked with the dietary supplement industry since 1985 and is a speaker on the topics of dietary supplements, alternative nutrition, and fad diets.

References are available upon request by e-mailing TDeditor@gvpub.com.

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