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Branched-Chain Amino Acids in elderly

Sarcopenia, the gradual loss of lean muscle mass associated with middle- and especially high-age, contributes to the fragility of an aging person. There is no clear consensus on how to blunt the process, but it is reasonable to claim that absence of chronic disease in a combination with physical activity and a healthy diet rich high-quality protein are the key factors.

Because the anabolic capacity of skeletal muscle decreases with age and there is no apparent harm associated with protein intake above the Recommended Dietary Allowance (RDA, the current RDA is 0.83 g protein/kg body weight/day), high protein diets were already proposed for elderly adults (Wolfe, Br J Nutr 2012;108:S88-S93).

However, the quality of long-term ingested dietary protein in terms of essential amino acids content, and especially leucine content, comes up as more important than quantity of the protein eaten (Paddon-Jones, Exp Gerontol. 2006;41(2):215-219).

Leucine and the two other branched-chain amino acids (BCAA) belong to the most studied group of amino acids with respect to muscular functions in both young and elderly humans. The unique role of leucine as the trigger of muscle synthesis is well studied (e.g. Valerio, Aging 2011;3:464-478). Clinical data support leucine central role in muscle protein synthesis, nitrogen provision for synthesis of other amino acids, as well as its role as an insulin stimulant.

Importantly, the beneficial effects of leucine were identified in both young and elderly humans. Among others, Koopman and colleagues reported that ingesting whey protein and 13 g leucine following physical activity resulted in similar increases in muscle strength/mass and body protein balance in young and eldely men (Koopman, Am J Clin Nutr 2006;84:623-632). Similar results, in addition to an enhanced rate of skeletal muscle synthesis, were obtained with another larger group of elderly adults supplementing for two weeks their normal diet with 12 g leucine per day (Casperson, Clin Nutr. 2012;31(4):512-519).

A different approach often used in clinical research involves the administration of a mixture of all nine essential amino acids in addition to extra high leucine doses. From a summary of all comparable trials, one could deduce that the minimum dose of leucine to stimulate muscle growth and strength in the elderly was at least 3 g leucine (i.e., Paddon-Jones, Curr Opin Clin Nutr Metab Care 2009;12:86-90).

It is also of value to note that leucine and BCAA mixtures have been reported to exert beneficial effects on body weight and body fat control in middle-aged individuals (Qin, J Nutr 2011;141:249-254). These epidemiological data on the importance of leucine in body weight management were further supported by interventional findings (i.e., Zanchi, Med Hypotheses 2012;79:883-888).

Taken together, clinical results have been very promising and demonstrated the key role of leucine and other branched-chain amino acids (BCAA) in tackling muscle loss in elderly, although it is important to note that physical activity, glucose metabolism and background intake of dietary protein are also very important factors.