Mixed
Protein supplementation during endurance training significantly improves time to exhaustion (TTE) with a moderate effect size, despite having no significant effect on maximal oxygen uptake (VO2max) or body composition in the general population.
If you are doing endurance training, adding protein supplements will likely help you exercise for a longer time before exhaustion. However, do not expect this to significantly change your body weight, body fat, or maximum oxygen capacity (VO2max) unless you are currently untrained. Focus on the performance duration benefit rather than body composition changes.
The results showed that protein supplementation during endurance training led to a small, nonsignificant increase in lean body mass (SMD = 0.13, 95% CI: −0.01, 0.28; p = 0.07) and a significant improvement in time to exhaustion (TTE) during endurance exercise (SMD = 0.45, 95% CI: 0.15, 0.76; p < 0.01). While the overall impact on maximal oxygen uptake (VO2max) was not significant... protein supplementation did not lead to significant changes in these outcomes, nor did it significantly affect body weight or body fat.
Why this rating
Based on a systematic review and meta-analysis of 23 RCTs with 1,146 participants, showing low heterogeneity for TTE.
Source
Effects of protein supplementation on body composition, physiological adaptations, and performance during endurance training: a systematic review and meta-analysis
Yang Xiao et al. · Frontiers in Nutrition · 2025
DOI 10.3389/fnut.2025.1663860
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