Dose-response effects of dietary protein on muscle protein synthesis during recovery from endurance exercise in young men: a double-blind randomized trial.
Level 2 - randomized trial
Individual randomized controlled trial
PubMed 32359142 · doi:10.1093/ajcn/nqaa073
What was done
In a double-blind, parallel-group randomized trial, 48 healthy, endurance-trained young men (mean age 27 ± 1 years) completed a single bout of endurance exercise followed by a 360-minute recovery period with primed continuous amino acid tracer infusions. Participants ingested 45 g of carbohydrate combined with 0 g (0 g PRO), 15 g (15 g PRO), 30 g (30 g PRO), or 45 g (45 g PRO) of intrinsically labeled milk protein. Blood and muscle biopsy samples were collected over 360 minutes to measure whole-body protein balance, myofibrillar protein synthesis (MyoPS), and mitochondrial protein synthesis (MitoPS).
What was found
Approximately 70% to 74% of ingested protein-derived phenylalanine appeared in circulation. Whole-body net protein balance increased dose-dependently across the 0, 15, 30, and 45 g groups (-0.31 ± 0.16, 5.08 ± 0.21, 10.04 ± 0.30, and 13.49 ± 0.55 μmol phenylalanine · kg⁻¹ · h⁻¹, respectively; P < 0.001). Ingestion of 30 g PRO stimulated a ~46% increase in MyoPS rates compared with 0 g PRO and was sufficient to maximize MyoPS. Overall MitoPS rates did not increase after protein ingestion, but incorporation of dietary amino acids into de novo mitochondrial protein increased dose-dependently across the 15, 30, and 45 g groups (0.018 ± 0.002, 0.034 ± 0.002, and 0.046 ± 0.003 mole percentage excess, respectively; P < 0.001).
Why it matters
This study establishes that 30 g of dietary protein co-ingested with carbohydrate is sufficient to maximize myofibrillar protein synthesis after endurance exercise, while whole-body balance and mitochondrial amino acid incorporation increase dose-dependently up to 45 g.
Limits
The study was conducted exclusively in young, endurance-trained men (n = 12 per parallel arm), limiting generalizability to women, older adults, or untrained individuals. It evaluated acute 6-hour recovery dynamics after a single exercise bout rather than chronic training adaptations.
Cited by
- supports A study from Luc van Loon's lab evaluating protein doses of 0, 15, 30, and 45 grams showed a non-linear dose-response relationship for muscle protein synthesis that continued to increase above 30 grams.