Leucine or Protein Supplementation and Resistance Training

The purpose of this study was to determine the effects of L-leucine (LEU) or different protein supplements standardized to LEU (\~3.0 g/serving) on changes in body composition, strength, and histological attributes in skeletal muscle and adipose tissue. Seventy-five untrained, college-aged males (mean±SE; age=21±1 yr, body mass=79.2±0.3 kg) were randomly assigned to an isocaloric, lipid-, and organoleptically-matched maltodextrin placebo (PLA, n=15), LEU (n=14), whey protein concentrate (WPC, n=17), whey protein hydrolysate (WPH, n=14), or soy protein concentrate (SPC, n=15) group. Participants performed whole-body resistance training three days per week for 12 weeks while consuming supplements twice daily. Skeletal muscle and subcutaneous (SQ) fat biopsies were obtained at baseline (T1) and \~72 h following the last day of training (T39). Tissue samples were analyzed for changes in type I and II fiber cross sectional area (CSA), non-fiber specific satellite cell count, and SQ adipocyte CSA. On average, all supplement groups including PLA exhibited similar training volumes and experienced statistically similar increases in total body skeletal muscle mass determined by dual x-ray absorptiometry (+2.2 kg; time p=0.024) and type I and II fiber CSA increases (+394 µm2 and +927 µm2; time p\<0.001 and 0.024, respectively). Notably, all groups reported increasing Calorie intakes \~600-800 kcal/d from T1 to T39 (time p\<0.001), and all groups consumed at least 1.1 g/kg/d of protein at T1 and 1.3 g/kg/d at T39. There was a training, but no supplementation, effect regarding the reduction in SQ adipocyte CSA (-210 µm2; time p=0.001). Interestingly, satellite cell counts within the WPC (p\<0.05) and WPH (p\<0.05) groups were greater at T39 relative to T1. In summary, LEU or protein supplementation (standardized to LEU content) does not provide added benefit in increasing whole-body skeletal muscle mass or strength above PLA following 3 months of training in previously untrained