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

2025-08-07
Frontiers in nutrition 12
- Yang Xiao
- ZhengWu Deng
- Wei Sun
- JiaYi Li
- WeiFeng Gao

PubMed: 40851900
DOI: 10.3389/fnut.2025.1663860

Study Design

Type: Systematic Review
Sample size: n = 146
Population: 23 randomized cross-over trials involving 1,146 participants
Methods: Systematic search in Web of Science, PubMed, and SPORTDiscus; meta-analysis using a random-effects model, standard mean difference

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 < 0.01). While the overall impact on maximal oxygen uptake (VO2max) was not significant, subgroup analysis revealed that untrained individuals may experience greater improvements in VO2max with protein supplementation (SMD = 0.21). Although aerobic and anaerobic capacities were assessed, protein supplementation did not lead to significant changes in these outcomes, nor did it significantly affect body weight or body fat.

Discussion

In summary, protein supplementation during endurance training appears to modestly enhance endurance performance (TTE) and may offer small benefits for lean body mass, particularly in untrained individuals. However, it does not significantly affect overall body weight, fat mass, or aerobic/anaerobic capacity in the general population.

Systematic review registration

Identifier, CRD420251034453, https://www.crd.york.ac.uk/PROSPERO/recorddashboard.

Research Insights

Protein→Improved Aerobic Capacity
Although aerobic and anaerobic capacities were assessed, protein supplementation did not lead to significant changes in these outcomes
Effect
Neutral
Effect size
Small
Protein→Improved Anaerobic Capacity
Although aerobic and anaerobic capacities were assessed, protein supplementation did not lead to significant changes in these outcomes
Effect
Neutral
Effect size
Small
Protein→Improved Maximal Oxygen Uptake
While the overall impact on maximal oxygen uptake (VO2max) was not significant
Effect
Neutral
Effect size
Small
Protein→Improved Time to Exhaustion
a significant improvement in time to exhaustion (TTE) during endurance exercise (SMD = 0.45, 95% CI: 0.15, 0.76; p < 0.01)
Effect
Beneficial
Effect size
Moderate
Protein→Increased Lean Body Mass
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)
Effect
Neutral
Effect size
Small
Protein→Reduced Body Fat
nor did it significantly affect body weight or body fat
Effect
Neutral
Effect size
Small
Protein→Reduced Body Weight
protein supplementation did not lead to significant changes in these outcomes, nor did it significantly affect body weight
Effect
Neutral
Effect size
Small