It is known that Muscle Protein Synthesis (MPS) is controlled by the concentration of extracellular amino acids. That is simply the amount of amino acids within the blood either from infusion or by ingestion. MPS appears to reach a peak 2 hours after ingesting an amino acid source. The Branched Chain Amino Acid Leucine is known to be able to stimulate MPS directly.
Supplying energy alone (eating carbohydrates or lipids) will not prevent negative nitrogen balance (i.e. the breakdown of muscle protein) and only ingesting amino acids will maintain this “nitrogen balance”. If our goal is to prevent muscle breakdown (muscle protein catabolism), then in theory ingesting BCAAs or specifically Leucine will stimulate protein synthesis and inhibit protein degradation.
We all work hard to build muscle tissue so during periods of caloric restriction/dieting, we want to preserve as much muscle tissue as possible. Supplementing to provide a sufficient amount of Leucine to stimulate MPS and maintain “nitrogen balance” is a good idea during such periods.
However, the body still requires 9 “essential” amino acids and BCAA are only 3 of them. For muscle protein anabolism (building new muscle tissue) to occur, a “complete” essential amino acid supplement is preferred. Therefore, supplementing with an EAA supplement will provide the 9 essential amino acids required by the body to aid in muscle protein synthesis. More importantly, the concentration of Leucine in an EAA supplement will be an important consideration. An EAA supplement with close to 3g Leucine is preferred, showing a greater increase in MPS compared to an EAA supplement with 1.87g Leucine.