Leucine promotes muscle protein synthesis via two different methods. Both, lead to the activation of mTOR — the fundamental route to all cell synthesis in the body. Studies have shown that adding a leucine supplement to your diet improves the synthesis of muscle protein.
Leucine’s effects on muscles focus on the production of skeletal protein, this means that the additional protein is produced as muscle mass. Leucine works as an anabolic trigger, and is metabolized directly in muscle tissue. Increasing muscle protein synthesis keeps you in a state of positive nitrogen balance, which is what you want to be if you’re trying to build muscle mass.
Leucine is the amino acid that is thought to be most potent at stimulating MPS. Peak plasma leucine concentrations following protein ingestion typically correlate with muscle protein synthesis rates (Pennings, 2011). This supports the notion that protein digestion rate and protein leucine content are important predictors for anabolic effect of a protein source.