Protein Requirements Are Increased in Endurance-Trained Athletes but Similar between Females and Males during Postexercise Recovery.
Level 2 - randomized trial
Within-subject crossover metabolic trial evaluating dose-response via stable isotope tracer
PubMed 37710376 · doi:10.1249/MSS.0000000000003219
What was done
Eight male (30 ± 3 yr) and seven female (30 ± 4 yr, tested in the midluteal phase) endurance athletes completed an indicator amino acid oxidation protocol. Following 2 days of controlled diet (1.4 g protein/kg/d) and running training (10 km/d and 5 km/d), participants ran 20 km and completed trials testing three protein intakes (0.2, 1.2, and 2.0 g/kg/d) given as a crystalline amino acid mixture with [1-13C]phenylalanine. Phenylalanine flux and oxidation (PheOx) were measured via breath and urine to estimate breakpoints in whole-body protein synthesis using modified biphasic linear regression.
What was found
PheOx differed significantly across protein intake levels (P < 0.01) with no main effect of sex (P = 0.63). Breakpoints did not differ between males and females (1.60 vs 1.61 g/kg/d, P = 0.94). Recommended intakes based on the upper 95% confidence interval were 1.81 g/kg/d for males and 1.89 g/kg/d for females.
Why it matters
This study shows endurance runners require protein intakes near the upper range of current sports guidelines (~1.85 g/kg/d) to support postexercise recovery, with equivalent requirements per kilogram between men and women.
Limits
The sample was small (n = 15 total: 8 males, 7 females). The breakpoint model relied on a 3-point intake curve rather than a multi-dose titration. Females were assessed only in the midluteal phase. Protein was administered as a crystalline amino acid mixture rather than whole foods, and outcomes reflect acute recovery from a single 20-km run.
Cited by
- supports In endurance athletes, higher protein intake improves exercise recovery up to approximately 1.6 to 1.8 grams per kilogram of body weight.