The Muscle Protein Synthetic Response to Whey Protein Ingestion Is Greater in Middle-Aged Women Compared With Men

Rationale: Muscle mass maintenance is largely regulated by the postprandial rise in muscle protein synthesis rates. It remains unclear whether postprandial protein handling differs between women and men.Methods: Healthy men (43 +/- 3 years; body mass index, 23.4 +/- 0.4 kg/m(2); n = 12) and women (46 +/- 2 years; body mass index, 21.3 +/- 0.5 kg/m(2); n = 12) received primed continuous infusions of L-[ring-H-2(5)]-phenylalanine and L-[ring-3,5-H-2(2)]-tyrosine and ingested 25 g intrinsically L-[1-C-13]-phenylalanine-labeled whey protein. Blood samples and muscle biopsies were collected to assess dietary protein digestion and amino acid absorption kinetics as well as basal and postprandial myofibrillar protein synthesis rates.Results: Plasma phenylalanine and leucine concentrations rapidly increased after protein ingestion (both P Conclusions: There are no differences in postabsorptive myofibrillar protein synthesis rates between middle-aged women and men. The myofibrillar protein synthetic response to the ingestion of 25 g whey protein is greater in women than in men.