Purpose: This investigation examined the effect of variations in protein intake on whole-body protein turnover (WBPTO) after exercise in endurance-trained males.
Methods: Five male runners (21.3 ± 0.3 yr, 179 ± 2 cm, 70.6 ± 0.1 kg, 8.7 ± 0.4% body fat, 70.6 ± 0.1 V˙O2peak) participated in a randomized, crossover-design diet intervention, where they consumed either a low- (0.8 g·kg−1; LP), moderate- (1.8 g·kg−1; MP), or high-protein (3.6 g·kg−1; HP) diet for 4 wk. WBPTO (Ra, leucine rate of appearance; NOLD, nonoxidative leucine disposal; and Ox, leucine oxidation) were assessed after a 75-min run at 70% V˙O2peak after each diet-intervention period.
Results: Leucine Ra (indicator of protein breakdown) and leucine Ox were greater on the HP diet than on the LP diet (Ra, 123.4 ± 6.9 vs 97.9 ± 6.0 μmol·kg−1·h−1; Ox, 23.9 ± 0.5 vs 17.0 ± 0.8 μmol·kg−1·h−1, P < 0.05). No differences were noted in NOLD (an indicator of protein synthesis) across diets. Plasma branched chain amino acids (BCAA) at rest were greater for MP and HP than for LP, and nonessential amino acids (NEAA) were greater for LP than MP at rest and greater than MP and HP after exercise.
Conclusion: Findings from this study show that variations in protein intake can alter plasma amino acid levels and modulate rates of WBPTO after exercise. Additionally, a lower protein intake was associated with decreased rates of WBPTO after exercise.