From Sup Watch
Branched chain amino acids are three essential amino acids; leucine, valine and isoleucine. The recommended dietary allowance for the BCAA is about 3 grams per day – an amount that should be easily obtained from protein foods. Supplemental levels have been used at levels around 5-20 grams per day.
Claims
Increased endurance
Prevention of fatigue
Improved mental performance
Increased energy levels
Theory
The idea behind BCAA supplements relates to a phenomenon known as central fatigue, which holds that mental fatigue in the brain can adversely affect physical performance in endurance events. The central fatigue theory suggests that low blood levels of BCAA may accelerate the production of serotonin, a key neurotransmitter in the brain, and prematurely lead to fatigue. Increase serotonin levels in the brain may depress the central nervous system function and lead to feelings of sleepiness and fatigue. Tryptophan, an amino acid that circulates in the blood, is a precursor of serotonin, and can be more easily transported into the brain to increase serotonin levels when BCAA levels in the blood are low (because high blood levels of BCAA can block tryptophan transport into the brain). During exercise, as muscle and liver glycogen are depleted for energy, blood levels of BCAA may also decrease and fatty acid levels increase to serve as an additional energy source. The problem with extra fatty acids in the blood is that they need to attach to a carrier protein called albumin for proper transport. In doing so, the fatty acids displace tryptophan from its place on albumin and facilitate the transport of tryptophan into the brain for conversion into serotonin. Therefore, the combination of reduced BCAA and elevated fatty acids in the blood, more tryptophan enters the brain and more serotonin is produced, leading to fatigue. Supplementing the diet with additional levels of BCAA is thought to block the tryptophan transport and, therefore, delay fatigue.
Scientific Support
Although the general theory of central fatigue and BCAA supplementation is sound, the research findings have not all been positive. In general, however, acute BCAA supplementation (right before exercise) has been shown to increase mental performance, improve cycling endurance, and reduce the time to complete a marathon. Chronic BCAA supplementation (2 weeks) has also been shown effective in improving time-trialing performance in trained cyclists. There are, however, a number of studies in trained and untrained subjects that have shown no effect of BCAA supplements on exercise performance or mental performance. In some cases, BCAA have been compared to carbohydrate supplementation during exercise with similar results (both delay fatigue to similar degrees).
Safety
Supplemental intakes of the BCAAs have been studied in the range of 5-20 grams per day in tablet form and 1 to 7 grams per liter in liquid form with no adverse side effects. Higher intakes should be avoided due to the possibility of competitive inhibition of the absorption of other amino acids from the diet and the risk of gastrointestinal distress.
Value
For endurance athletes, particularly those competing in longer races (2+ hours) such as marathons, triathlons, road cycling, backpacking and orienteering, BCAA supplements may be warranted to help delay central fatigue. Participation in shorter duration events is unlikely to result in substantial changes in blood levels of BCAA, tryptophan or fatty acids, so BCAA supplementation is probably not needed.
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