Dose-Dependent Increases in Whole-Body Net Protein Balance and Dietary Protein-Derived Amino Acid Incorporation into Myofibrillar Protein During Recovery from Resistance Exercise in Older Men.
Level 2 - randomized trial
Individual randomized controlled trial
PubMed 30722014 · doi:10.1093/jn/nxy263
What was done
Forty-eight healthy older men (mean ± SEM age: 66 ± 1 y; BMI: 25.4 ± 0.3 kg/m²) were randomized to ingest 0, 15, 30, or 45 g of milk protein concentrate after a single whole-body resistance exercise bout (leg press, leg extension, lat pulldown, chest press at 75–80% 1RM). Researchers evaluated protein digestion and absorption kinetics, whole-body protein balance, and myofibrillar protein synthesis rates using primed, continuous stable isotope infusions combined with intrinsically labeled milk protein.
What was found
Whole-body net protein balance increased dose-dependently across the 0, 15, 30, and 45 g groups (0.015 ± 0.002, 0.108 ± 0.004, 0.162 ± 0.008, and 0.215 ± 0.009 μmol Phe · kg⁻¹ · min⁻¹, respectively; P < 0.001). Myofibrillar protein synthesis rates were higher after 30 g (0.0951 ± 0.0062%/h, P = 0.07) and 45 g (0.0970 ± 0.0062%/h, P < 0.05) compared to 0 g (0.0746 ± 0.0051%/h). Dietary protein-derived amino acid incorporation into de novo myofibrillar protein rose dose-dependently after 15, 30, and 45 g (0.0171 ± 0.0017, 0.0296 ± 0.0030, and 0.0397 ± 0.0026 mole percentage excess, respectively; P < 0.05).
Why it matters
Older adults require at least 30 g of protein post-exercise to stimulate myofibrillar protein synthesis, with whole-body protein balance continuing to improve up to 45 g.
Limits
The study tested only acute responses to a single bout of exercise, not chronic training adaptations or long-term muscle mass changes. The cohort was restricted to healthy older men (12 per group), limiting generalizability to women, frail/sarcopenic individuals, or other protein sources.
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.