Leucine supplementation of a low-protein mixed macronutrient beverage enhances myofibrillar protein synthesis in young men: a double-blind, randomized trial

• Published in: The American journal of clinical nutrition 2014-02, Vol.99 (2), p.276-286
• Main Authors: Churchward-Venne, Tyler A, Breen, Leigh, Di Donato, Danielle M, Hector, Amy J, Mitchell, Cameron J, Moore, Daniel R, Stellingwerff, Trent, Breuille, Denis, Offord, Elizabeth A, Baker, Steven K, Phillips, Stuart M
• Format: Article
• Language: English
• Subjects: Adolescent; Adult; Amino acids; Amino Acids, Branched-Chain - administration & dosage; Beverages; blood; Blood Glucose - metabolism; branched chain amino acids; clinical nutrition; Clinical trials; Diet, Protein-Restricted; Dietary Proteins - administration & dosage; Dietary Supplements; Dose-Response Relationship, Drug; Double-Blind Method; Humans; ingestion; Insulin - blood; isoleucine; leucine; Leucine - administration & dosage; Leucine - blood; Linear Models; Male; men; Milk Proteins - administration & dosage; muscle protein; Muscle, Skeletal - drug effects; Muscle, Skeletal - metabolism; muscles; Musculoskeletal system; Myofibrils - drug effects; Myofibrils - metabolism; phenylalanine; Phenylalanine - administration & dosage; Phenylalanine - blood; Protein Biosynthesis - drug effects; Protein synthesis; Resistance Training; Rest - physiology; skeletal muscle; strength training; valine; whey protein; Whey Proteins; Young Adult
• ISSN: 0002-9165; 1938-3207
• DOI: 10.3945/ajcn.113.068775

Background: Leucine is a key amino acid involved in the regulation of skeletal muscle protein synthesis.Objective: We assessed the effect of the supplementation of a lower-protein mixed macronutrient beverage with varying doses of leucine or a mixture of branched chain amino acids (BCAAs) on myofibrillar protein synthesis (MPS) at rest and after exercise.Design: In a parallel group design, 40 men (21 ± 1 y) completed unilateral knee-extensor resistance exercise before the ingestion of 25 g whey protein (W25) (3.0 g leucine), 6.25 g whey protein (W6) (0.75g leucine), 6.25 g whey protein supplemented with leucine to 3.0 g total leucine (W6+Low-Leu), 6.25 g whey protein supplemented with leucine to 5.0 g total leucine (W6+High-Leu), or 6.25 g whey protein supplemented with leucine, isoleucine, and valine to 5.0 g total leucine. A primed continuous infusion of l-[ring-13C6] phenylalanine with serial muscle biopsies was used to measure MPS under baseline fasted and postprandial conditions in both a rested (response to feeding) and exercised (response to combined feeding and resistance exercise) leg.Results: The area under the blood leucine curve was greatest for the W6+High-Leu group compared with the W6 and W6+Low-Leu groups (P < 0.001). In the postprandial period, rates of MPS were increased above baseline over 0–1.5 h in all treatments. Over 1.5–4.5 h, MPS remained increased above baseline after all treatments but was greatest after W25 (∼267%) and W6+High-Leu (∼220%) treatments (P = 0.002).Conclusions: A low-protein (6.25 g) mixed macronutrient beverage can be as effective as a high-protein dose (25 g) at stimulating increased MPS rates when supplemented with a high (5.0 g total leucine) amount of leucine. These results have important implications for formulations of protein beverages designed to enhance muscle anabolism. This trial was registered at clinicaltrials.gov as NCT 1530646.