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.