Myofibrillar muscle protein synthesis rates subsequent to a meal in response to increasing doses of whey protein at rest and after resistance exercise.
Oliver C Witard, Sarah R Jackman, Leigh Breen, Kenneth Smith, Anna Selby, Kevin D Tipton
Author Information
Oliver C Witard: Health and Exercise Science Research Group, University of Stirling, Stirling, United Kingdom (OCW and KDT); Sport and Health Sciences, College of Life and Environmental Sciences, University of Exeter, Exeter, United Kingdom (SRJ); the School of Sport and Exercise Sciences, University of Birmingham, Birmingham, United Kingdom (LB); and Metabolic Physiology, Medical Research Council and Arthritis Research United Kingdom Centre for Excellence in Musculoskeletal Ageing, School of Graduate Entry Medicine and Health, University of Nottingham, Derby, United Kingdom (KS and AS).
BACKGROUND: The intake of whey, compared with casein and soy protein intakes, stimulates a greater acute response of muscle protein synthesis (MPS) to protein ingestion in rested and exercised muscle. OBJECTIVE: We characterized the dose-response relation of postabsorptive rates of myofibrillar MPS to increasing amounts of whey protein at rest and after exercise in resistance-trained, young men. DESIGN: Volunteers (n = 48) consumed a standardized, high-protein (0.54 g/kg body mass) breakfast. Three hours later, a bout of unilateral exercise (8 × 10 leg presses and leg extensions; 80% one-repetition maximum) was performed. Volunteers ingested 0, 10, 20, or 40 g whey protein isolate immediately (~10 min) after exercise. Postabsorptive rates of myofibrillar MPS and whole-body rates of phenylalanine oxidation and urea production were measured over a 4-h postdrink period by continuous tracer infusion of labeled [(13)C6] phenylalanine and [(15)N2] urea. RESULTS: Myofibrillar MPS (mean ± SD) increased (P < 0.05) above 0 g whey protein (0.041 ± 0.015%/h) by 49% and 56% with the ingestion of 20 and 40 g whey protein, respectively, whereas no additional stimulation was observed with 10 g whey protein (P > 0.05). Rates of phenylalanine oxidation and urea production increased with the ingestion of 40 g whey protein. CONCLUSIONS: A 20-g dose of whey protein is sufficient for the maximal stimulation of postabsorptive rates of myofibrillar MPS in rested and exercised muscle of ~80-kg resistance-trained, young men. A dose of whey protein >20 g stimulates amino acid oxidation and ureagenesis. This trial was registered at http://www.isrctn.org/ as ISRCTN92528122.
