Whey protein stimulates postprandial muscle protein accretion more effectively than do casein and casein hydrolysate in older men.
Level 2 - randomized trial
Individual randomized controlled trial
PubMed 21367943 · doi:10.3945/ajcn.110.008102
What was done
Forty-eight healthy older men (mean age 74 ± 1 y) were randomly assigned to ingest 20 g of intrinsically L-[1-13C]phenylalanine-labeled whey, casein, or casein hydrolysate. Protein ingestion was combined with continuous intravenous L-[ring-2H5]phenylalanine infusion to assess in vivo digestion and absorption kinetics and determine postprandial mixed muscle protein fractional synthetic rates (FSR).
What was found
The peak appearance rate of dietary-derived phenylalanine in circulation was greater after whey and casein hydrolysate than after casein (P < 0.05). Muscle FSR was significantly higher following whey ingestion (0.15 ± 0.02%/h) compared to casein (0.08 ± 0.01%/h; P < 0.01) and casein hydrolysate (0.10 ± 0.01%/h; P < 0.05). Peak plasma leucine concentrations showed a positive correlation with postprandial FSR values (r = 0.66, P < 0.01).
Why it matters
It demonstrates that protein quality and digestion kinetics directly affect the acute muscle protein synthetic response in older adults, showing that whey protein stimulates greater short-term muscle protein accretion than casein forms.
Limits
The study tested only a single 20 g dose in an acute setting, without measuring long-term changes in muscle mass, physical performance, or strength. The cohort was restricted entirely to healthy older men (approximately 16 per arm), limiting generalizability to women, frail individuals, or chronic dietary patterns.
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.
- supports Hydrolyzing casein to match the rapid digestion and absorption rate of whey still results in a lower muscle protein synthesis response, which can be overcome by adding free leucine.