Amino acids and muscle loss with aging.

Aging is associated with a progressive loss of muscle mass (sarcopenia), which increases the risks of injury and disability. Although the mechanisms of sarcopenia are not clearly elucidated, age-associated alterations in the muscle anabolic response to nutritional stimuli and a decline in protein intake may be significant contributing factors. The most recent findings regarding the role of nutritional intake on protein metabolism in the elderly will be reviewed. Specifically, aging is associated with changes in the muscle protein metabolism response to a meal, likely due to alterations in the response to endogenous hormones. Nonetheless, the older muscle is still able to respond to amino acids, mainly the essential and BCAAs, which have been shown to acutely stimulate muscle protein synthesis in older individuals. It is likely that this stimulatory effect of essential and BCAA is due to the direct effect of leucine on the initiation of mRNA translation, which is still present in older age, although it appears to be attenuated in aged animals. Recent data suggest that excess leucine may be able to overcome this age-related resistance of muscle proteins to leucine. For this reason, long-term essential amino acid supplementation may be a useful tool for the prevention and treatment of sarcopenia, particularly if excess leucine is provided in the supplement.