Protein supplementation and resistance training-induced strength gains in young adults: a meta-analysis.
Zhang C, Wang Y, Huang W. · Frontiers in nutrition · 2026
Background: This study aimed to determine whether protein supplementation confers additional benefits for muscle strength gains beyond those induced by resistance training (RT) alone in healthy young adults.
Methods: A systematic literature search was performed in PubMed, Web of Science, Cochrane Library, and SPORTDiscus through April 1, 2026. Twenty-three randomized controlled trials involving 611 healthy young adults were included. Pooled estimates were calculated as weighted mean differences (WMD) with 95% confidence intervals (CIs) using a random-effects model. Subgroup analysis, meta-regression, and leave-one-out and leave-one-category-out sensitivity analysis were performed to explore heterogeneity.
Results: Compared with RT alone, combined RT and protein supplementation produced significant improvements in both bench press (WMD: 2.63 kg, 95% CI: 0.77-4.49, p = 0.006) and squat strength (WMD: 7.40 kg, 95% CI: 2.15-12.66, p = 0.006). Subgroup analysis revealed that the ergogenic effect on squat strength was predominantly observed when the intervention lasted ≤12 weeks, or when protein was ingested both around exercise (pre- and/or post-exercise) and before sleep. Meta-regression identified intervention duration as a significant moderator ( p = 0.037) and protein timing as a borderline moderator ( p = 0.073) of squat strength heterogeneity. Sensitivity analysis showed that the pooled effects remained significant and consistent in direction.
Conclusion: Protein supplementation combined with resistance training enhances muscle strength in young healthy adults, but its incremental benefit appears conditional on intervention duration, nutrient timing, training
background, and baseline protein status rather than universally applicable. Future well-powered trials with standardized protein dose and source reporting, repeated measures of habitual protein intake, and stratified designs are needed to clarify these interactions and support more personalized, mechanism-informed exercise and nutrition guidance. Systematic review registration https://www.crd.york.ac.uk/PROSPERO/# myprospero, PROSPERO, identifier: CRD42024534481.