Myofibrillar muscle protein synthesis rates subsequent to a meal in response to increasing doses of whey protein at rest and after resistance exercise

• Published in: The American journal of clinical nutrition 2014-01, Vol.99 (1), p.86-95
• Main Authors: Witard, Oliver C, Jackman, Sarah R, Breen, Leigh, Smith, Kenneth, Selby, Anna, Tipton, Kevin D
• Format: Article
• Language: English
• Subjects: Adult; Amino acids; Amino Acids - metabolism; Blood Glucose - metabolism; Body Mass Index; Diet; Dose-Response Relationship, Drug; Exercise; Humans; Male; Meals; Milk Proteins - administration & dosage; Muscle Proteins - biosynthesis; Myofibrils - metabolism; Oxidation; Phenylalanine - metabolism; Protein Biosynthesis; Protein synthesis; Resistance Training; Rest - physiology; Single-Blind Method; Whey Proteins; Young Adult
• ISSN: 0002-9165; 1938-3207
• DOI: 10.3945/ajcn.112.055517

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. 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. 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. 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. 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.