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Whey is renowned for being a high quality protein source because it has a high concentration of essential amino acids. Whey is also particularly high in the branched-chain amino acids like leucine. Previous research has shown only the essential amino acids are necessary to increase protein synthesis. Therefore it would be predicted that if the free form of the essential amino acids in whey were provided, you should get the same increase in the protein synthesis; at least that is what researchers thought. The study involved 3 feeding trials. One treatment had subjects ingest 15 grams of whey protein. In the other two trials, they ingested whey's constituent essential amino acids (about 7) and nonessential amino acids (8 g). Protein balance was measured for 3.5 hours after ingestion. The nonessential amino acid trial resulted in essentially no change in protein balance as indicated by the change in leg phenylalanine balance, whereas the essential amino acid trial resulted in a small increase of about 25 mmol/kg lean leg mass. However after whey ingestion, phenylalanine balance was markedly increased to over 100 mmol/kg lean leg mass. The findings were somewhat surprising because it indicates that that the essential amino acids content of whey is not solely responsible for the anabolic effects. The results have implications for formulation of protein supplements and suggest free amino acids given at these dosages do not result in the same anabolic effect as intact whey.

Katsanos CS, Chinkes DL, Paddon-Jones D, Zhang XJ, Aarsland A, Wolfe RR. Whey protein ingestion in elderly persons results in greater muscle protein accrual than ingestion of its constituent essential amino acid content. Nutr Res. 2008 Oct;28(10):651-8.