Ingestion of whey hydrolysate, casein, or soy protein isolate: effects on mixed muscle protein synthesis at rest and following resistance exercise in young men.
Level 2 - randomized trial
Parallel-group controlled trial
PubMed 19589961 · doi:10.1152/japplphysiol.00076.2009
What was done
Eighteen healthy young men were divided into three groups (n = 6 per group) to compare acute mixed muscle protein synthesis (MPS) responses to different protein sources. Participants performed a bout of unilateral leg resistance exercise followed by ingestion of a beverage containing an equivalent content of essential amino acids (10 g) as whey hydrolysate, micellar casein, or soy protein isolate. Mixed MPS was determined using a primed constant infusion of l-[ring-13C6]phenylalanine in both the exercised and nonexercised (resting) legs.
What was found
Whey protein ingestion resulted in larger increases in blood essential amino acid, branched-chain amino acid, and leucine concentrations than casein or soy (P < 0.05). Mixed MPS at rest was 0.091 ± 0.015%/h for whey, 0.078 ± 0.014%/h for soy, and 0.047 ± 0.008%/h for casein; whey was approximately 93% greater than casein (P < 0.01) and approximately 18% greater than soy (P = 0.067). Post-exercise MPS for whey was approximately 122% greater than casein (P < 0.01) and 31% greater than soy (P < 0.05). Soy stimulated greater MPS than casein at rest (64%, P < 0.01) and post-exercise (69%, P < 0.01).
Why it matters
This study demonstrates that digestion rate and amino acid composition (especially leucine) strongly influence acute postprandial muscle protein synthesis, with rapidly digested whey hydrolysate eliciting a superior anabolic response compared to soy or casein.
Limits
The sample size was very small (n = 6 per group, total n = 18) and limited exclusively to young men. The trial only measured acute, short-term fractional synthetic rates from a single meal rather than chronic adaptations in muscle mass or strength.
Cited by
- supports Micellar casein is a slowly digested protein that induces a slower rise in plasma essential amino acids and a lower muscle protein synthesis response compared to whey protein.