Effects of protein supplementation on body composition, physiological adaptations, and performance during endurance training: a systematic review and meta-analysis

Introduction:

This study aimed to evaluate the long-term effects of endurance training combined with protein supplementation on body composition, physiological adaptations (aerobic/anaerobic capacity), and performance.

Methods:

A systematic search was conducted in Web of Science, PubMed, and SPORTDiscus databases on April 16, 2025, using the keywords “endurance training” and “protein supplementation.” Meta-analysis was conducted using a random-effects model, and the main effect size of each outcome was summarized using the standard mean difference (SMD), and moderators were explored using subgroup and regression analyses.

Results:

A total of 23 randomized cross-over trials involving 1,146 participants were included. 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 .

Protein supplementation during endurance training may enhance performance and lean body mass, particularly in untrained individuals.