Myofibrillar muscle protein synthesis rates subsequent to a meal in response to increasing doses of whey protein at rest and after resistance exercise.
Level 2 - randomized trial
Individual randomized controlled trial measuring metabolic tracer kinetics.
PubMed 24257722 · doi:10.3945/ajcn.112.055517
What was done
Forty-eight resistance-trained young men (~80 kg body mass) consumed a standardized high-protein breakfast (0.54 g/kg body mass). Three hours later, they performed unilateral leg exercise (8 × 10 leg presses and extensions at 80% 1RM) and immediately ingested 0, 10, 20, or 40 g of whey protein isolate. Postabsorptive myofibrillar muscle protein synthesis (MPS) and whole-body rates of phenylalanine oxidation and urea production were assessed over a 4-hour post-drink period using continuous infusions of [(13)C6] phenylalanine and [(15)N2] urea tracers.
What was found
Myofibrillar MPS increased significantly above 0 g whey protein (0.041 ± 0.015%/h) by 49% with 20 g whey and by 56% with 40 g whey (both P < 0.05). Ingestion of 10 g whey protein did not significantly stimulate MPS above 0 g (P > 0.05), and 40 g did not significantly increase MPS over 20 g. Rates of whole-body phenylalanine oxidation and urea production increased significantly with 40 g whey protein.
Why it matters
It defines an acute per-meal ceiling for post-exercise whey protein dosing in trained young men, demonstrating that 20 g is sufficient to saturate myofibrillar protein synthesis, with excess protein redirected to oxidation and ureagenesis.
Limits
The sample was restricted to young, resistance-trained men weighing ~80 kg, limiting generalizability to women, older adults, or individuals with different body compositions. Outcomes were restricted to acute 4-hour postprandial tracer kinetics following isolated whey protein, rather than chronic training adaptations or whole-food meals.
Cited by
- supports In healthy young adults, ingesting 20 grams of high-quality protein maximally stimulates muscle protein synthesis over 4 to 6 hours, with 40 grams providing no further increase.
- supports Dose-response studies in healthy young individuals show that 20 grams of protein maximizes muscle protein synthesis at rest or post-exercise, with 40 grams showing no greater response over a 4 to 6 hour window.