Some but not all recent studies found that whey protein and leucine supplements increased protein synthesis. Amino acids act as the building blocks of protein, and leucine is a triggering mechanism for intracellular protein synthesis.

Michelle Mielke from the University of Pacific in California and colleagues found that supplementing a weight-training program with either whey protein + leucine or with carbohydrates had no more effect on strength, endurance or body composition than strength training alone. The training group did 2 sets of exercises (bench press and leg extensions), while the supplemented groups did only 1 set. This could mean that the supplements provided an added training effect, or that 1 set of each exercise provided the same training effect as 2 sets in beginning weight trainers. (Journal Exercise Physiologyonline, October 5, 2009)