Long-term effects of plant vs. animal protein supplementation on body composition, muscle strength, physical performance, and cardiometabolic risk factors in adults: a systematic review and meta-analysis of randomized controlled trials

Introduction Previous studies have yielded mixed results on the effects of supplementing with plant-based protein (PBP) isolates or concentrates vs. animal-based protein (ABP) on body composition, muscle strength, physical performance, and cardiometabolic risk factors. Consequently, it would be helpful to synthesize pooled evidence from randomized controlled trials (RCTs) on these parameters to assess the efficacy of different protein sources, particularly in the long term. Objective To assess the long-term effects (>= 6 months) of PBP compared to ABP supplementation on body composition, muscle strength, physical performance, and cardiometabolic risk factors in adults aged 18 and older. Methods PubMed, Scopus, and Web of Science databases were searched from their inception to 25 February 2025. Relevant studies were also searched by citation tracing. RCTs comparing PBP with ABP supplementation for at least 6 months were included. A random effects model was employed for data pooling. The overall effect estimate was presented using standardized mean difference (SMD) accompanied by a forest plot and prediction intervals.Results A total of 18 RCTs involving 1,893 participants met the criteria for inclusion in the systematic review and meta-analysis. In adults aged 18 years and older, long-term supplementation of PBP (largely soy protein) did not show statistically significant differences in lean body mass (LBM), fat mass (FM), total body mass (TBM), upper and lower muscle strength, gait speed (GS), chair stand test (CST), timed up and go (TUG) test, short physical performance battery (SPPB), lipid profiles, blood pressure, fasting blood glucose (FBG), fasting blood insulin (FBI), and homeostatic model assessment (HOMA-IR) for insulin resistance compared with ABP. Conclusion Long-term supplementation with PBP, compared with ABP, did not result in differences in body composition, muscle strength, physical performance, or cardiometabolic risk parameters in the adult population. Based on heterogeneity, the data dot provide clear evidence of differences observed between protein sources at present, as long as an adequate quantity of protein is consumed over time.Systematic review registration https://www.crd.york.ac.uk/PROSPERO/, Identifier CRD42024604240.