While all other amino acids are broken down in the liver; BCAAs are metabolized primarily in lean body mass tissue.1 Because of this, they could help improve exercise performance and also reduce the rate of lean body mass break down.
BCAA supplementation may promote lean body mass protein synthesis and also increase lean body mass in individuals who consume a low protein diet. 3 In one study, leucine and valine were found to cause a significant suppression in body weight loss in mice with cachexia (body-wasting). Both of these BCAAs caused a significant increase in muscle tissue, through an increase in protein synthesis and a decrease in degradation. 4
BCAA supplementation may also be effective in preventing fatigue in athletes and physically active people by halting a decline in serum BCAA levels which can occur during physical exertion. A decline in serum BCAA levels typically causes the influx of tryptophan into the brain, which is followed by increased serotonin production – which may result in fatigue. 5