Effect of whey and casein proteins on muscle protein synthesis after resistance exercise

The rate of protein digestion varies across amino acid sources and differentially affects whole‐body protein kinetics at rest. We investigated the effect of consuming whey or casein proteins on muscle protein synthesis (MPS) after an acute bout of unilateral resistance exercise. On three occasions, eight healthy resistance trained men (24.4 ± 4.8 yr; BMI = 27.1 ± 4.2 kg·m −2 ) performed a unilateral bout of resistance exercise and then consumed a drink containing 10g of essential amino acids in the form of whey protein, whey and casein (1:1), or casein protein. Mixed MPS was determined by pulse‐tracer injections of L‐[ring‐ 2 H 5 ] and L‐[ 15 N] phenylalanine 120–180 min after protein ingestion. The pattern of amino acid appearance in the blood after consuming the protein drinks was not affected by the source of amino acids. Rates of MPS were greater in the exercised compared to the non‐exercised leg (p < 0.05); however, there were no drink‐specific differences. Hence, while the source of amino acids may affect whole‐body protein kinetics, this effect is not apparent in skeletal muscle. We conclude that the ingestion of whey and casein proteins, in isolation or combination, stimulates mixed MPS to a similar extent after an acute bout of resistance exercise. Supported by the US National Dairy Council.