AGING alters the control of metabolic homeostasis and generates specific nutritional requirements. More specifically, protein homeostasis in aging muscle is threatened by an imbalance between catabolism and anabolism: While there is no difference in terms of proteolysis, the anabolic response of muscle to nutritional stimuli is weaker than it is in younger persons (1–3). This contributes to a progressive loss of muscle mass (so-called ‘‘sarcopenia’’), poor adaptation to food restriction (4,5), and a resistance to refeeding (6,7). Thus, although still a con- troversial point (8–10), protein requirements in terms of quantity are probably slightly higher in elderly than in young individuals (11). Furthermore, the quality of the proteins for protein metabolism appears to change during aging: As opposed to younger persons, protein gain is greater in elderly persons fed rapidly digested proteins (e.g., whey protein) than in elderly persons fed an isonitrogenous amount of slowly digested proteins (e.g., casein) (12). Aging is also associated with a decrease in insulin sen- sitivity (13); elderly populations are characterized by a high prevalence of impaired glucose tolerance (14) and an increased risk of developing diabetes with age, reaching 20% in persons older than 70 years (15).