Effects of combined protein and probiotic supplementation on physical performance and body composition: a Bayesian multilevel meta-analysis of randomized controlled trials.

Abstract

Protein supplementation is widely used to support muscle adaptation. Probiotics may also improve nutrient use, gut health, and recovery. However, evidence on their combined effects remains inconsistent. This study examined the effects of protein-plus-probiotic supplementation on physical performance and body composition using Bayesian multilevel meta-analysis. This review was prospectively registered in PROSPERO and conducted according to PRISMA. Randomized controlled trials in adults were identified through systematic database searches, with screening supported by ASReview and Covidence. Studies were included if they compared protein-plus-probiotic supplementation with placebo, protein alone, or other relevant controls, and reported outcomes on physical performance or body composition. Effect sizes were calculated as Hedges' g . Bayesian multilevel models were used to account for dependent effect sizes within studies. Twenty studies with 679 participants were included. The posterior estimate was positive for physical performance [Hedges' g : 0.45, 95% HDI: 0.21 to 0.67], whereas the estimate for body composition was close to null [Hedges' g : 0.02, 95% HDI: -0.14 to 0.20]. Signals of benefit were observed for muscle strength, muscular endurance, and lean mass, although these findings should be interpreted in light of outcome heterogeneity and study-level limitations. Current evidence suggests selective signals of benefit for protein-plus-probiotic supplementation. The intervention may be associated with better physical performance, particularly muscle strength and muscular endurance, whereas evidence for broad body-composition changes remains limited. For body composition, the most consistent signal was observed for lean mass or muscle mass. Further high-quality randomized trials are needed to clarify whether these signals are reproducible across probiotic strains, protein types, delivery forms, and populations. https://www.crd.york.ac.uk/PROSPERO/view/CRD420251165192, Registered at the international prospective register of systematic reviews (PROSPERO; CRD420251165192).