Contrarily to whey and high protein diets, dietary free leucine supplementation cannot reverse the lack of recovery of muscle mass after prolonged immobilization during ageing

Key points During ageing, there is a lack of recovery of muscle mass following immobilization. We showed, in old rats, an anabolic resistance of muscle protein synthesis to food intake during immobilization and only a slight increase of protein synthesis during the recovery, which explain a poor muscle nitrogen balance that is insufficient to induce a muscle mass gain. A supplementation with free leucine, an essential amino acid known to stimulate muscle protein metabolism, was efficient in inducing a greater anabolism but failed to induce muscle mass recovery. This discrepancy was explained by a desynchronization between the leucine signal and amino acids coming from dietary protein digestion. An induction of a larger increase and a longer availability of amino acids in the postprandial state with rich-protein leucine (i.e. whey) and high protein diets were efficient in inducing a muscle mass recovery after immobilization.