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Both forms of protein are derived from milk and using different comparison scale both are often rated at or near the top. In comparison to other protein sources, casein and whey contain some of the highest levels of the essential amino acids as well as the branched-chain amino acids and in particular leucine. While both sources exhibit high levels of critical amino acid components, key differences abound. Primarily the rate at which they are digested is often discussed as this factor dictates the appearance of amino acids into the blood and muscle. Faster rates for whey protein promote more growth, particularly for key proteins found in the muscle itself and slower rates for casein are suggested to offer a more balance, prolonged delivery of key amino acids.
To examine differences in the proteins in response to resistance exercise, scientists had young males participate in three study trials (Reitelseder, Agergaard et al. 2011). One trial provided casein, the other whey and the third and final was a placebo. Both proteins were given in doses based on lean body mass and likely ranged from 20 – 25 grams of each protein; all nutrition was consumed immediately after the exercise bout. Blood and muscle samples were analyzed to determine changes in key hormones linked to cellular growth, muscle protein synthesis as well as the expression of key components inside the muscle.
When rates of myofibrillar protein synthesis were determined over the course of several hours after the exercise bout, both types of protein were found to increase rates of myofibrillar protein synthesis to a greater extent than placebo, but no differences were found between casein and whey. Several components inside our human muscle are commonly measured by scientists to determine the extent to which changes in protein availability and exercise can influence their expression. Three of these proteins, Akt, 4E-BP1 and p70s6k were increased after exercise and protein intake, a favorable outcome when considering both of these components are linked with muscle growth.
The authors concluded as many authors have also concluded before that both types of protein were effective at increasing rates of muscle protein synthesis and promoting an overall anabolic environment inside the muscle. The amount of scientific support for utilizing key high quality proteins such as whey and casein at opportune times continues to grow. Both proteins are loaded with valuable amino acids and for this reason, do an excellent job of supporting your muscles in responding to a challenging resistance training program.
Reitelseder, S., J. Agergaard, et al. (2011). "Whey and casein labeled with L-[1-13C]leucine and muscle protein synthesis: effect of resistance exercise and protein ingestion." Am J Physiol Endocrinol Metab 300(1): E231-242.