Amino acid metabolism and intake in the elderly

Age-related sarcopenia is a major feature of aging with such negative consequences as disability and increased morbidity; it can also lead to undernutrition and frailty. Along with insufficient protein intake, amino acid metabolism is impaired, with a higher splanchnic extraction and a reduction of the anabolic effects of amino acids on muscle, mainly due to a lesser stimulation of the mTOR signalization pathway; an increased proteolysis (through the proteasome-ubiquitin complex) is also involved. As a consequence of these features, protein intake should never be below 1 g/kg per day. Bolus administration of proteins as well as the use of fast proteins are promising approaches. Last, administration of supraphysiological amounts of such amino acids as leucine, citrulline and arginine allows stimulation of protein synthesis, mainly through mTOR activation, and is an interesting alternative to drug treatment of sarcopenia. (C) 2008 Elsevier Masson SAS. Tous droits reserves.