Ingested protein dose response of muscle and albumin protein synthesis after resistance exercise in young men.
Level 2 - randomized trial
Individual randomized crossover metabolic trial in humans
PubMed 19056590 · doi:10.3945/ajcn.2008.26401
What was done
Six healthy young men completed an intense bout of leg resistance exercise on five separate occasions in a randomized crossover design. After exercise, participants consumed drinks containing 0, 5, 10, 20, or 40 g of whole egg protein in a randomized order. Muscle protein synthesis (MPS), albumin protein synthesis (APS), and whole-body leucine oxidation were measured over a 4-hour recovery period using a primed constant infusion of [1-(13)C]leucine. Phosphorylation of candidate signaling proteins (p70S6K Thr389, rpS6 Ser240/244, and eIF2B epsilon-subunit Ser539) was also assessed.
What was found
MPS increased in a dose-dependent manner and was maximally stimulated at 20 g of protein, with no further increase at 40 g. APS also increased dose-dependently and plateaued at 20 g. Leucine oxidation was significantly increased after ingestion of 20 and 40 g of protein. Phosphorylation of the measured signaling proteins was unaffected by the dose of protein ingested. Specific numerical values for protein synthesis rates and oxidation were not reported in the abstract.
Why it matters
This trial establishes that 20 g of intact high-quality protein maximally stimulates post-exercise muscle and albumin protein synthesis in young men, with higher doses driving irreversible amino acid oxidation rather than additional tissue synthesis.
Limits
The sample size was very small (n = 6) and restricted solely to healthy young men. The abstract reports no numerical values or variance estimates, and the design evaluated only acute 4-hour responses to egg protein following isolated leg exercise, which may not generalize to whole-body workouts, other protein sources, mixed meals, females, or older adults.
Cited by
- supports In younger individuals, 10 grams of protein can stimulate muscle protein synthesis, whereas older adults require closer to 20 to 40 grams per meal.
- supports A dose-response study by Stuart Phillips showed 20 grams of egg albumin protein maximized muscle protein synthesis statistically, with 40 grams producing an 11% higher rate that was not statistically significant.
- 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.