Effects of probiotics and synbiotics on body weight management in individuals with overweight or obesity: a systematic review and meta-analysis of randomized controlled trials

[Purpose] This meta-analysis examined whether short-term probiotic/synbiotic supplementation reduces body weight, BMI, fat mass, body fat percentage, and lean body mass in adults with overweight or obesity.[Methods] Electronic databases were searched for RCTs of probiotic or synbiotic interventions versus placebo. Study quality was assessed using the Cochrane Risk-of-Bias tool. Standardized mean differences (Hedges’ g; RevMan 5.4) were pooled using a random-effects model on post-intervention endpoint values.[Results] Ten RCTs (633 participants) were included. No significant differences were observed in body weight (9 studies, <i>n</i> = 592; SMD = -0.44; 95% CI: -0.92 to 0.04; I² = 87%) or lean body mass (5 studies, <i>n</i> = 342; SMD = -0.14; 95% CI: −0.53 to 0.25; I² = 69%). A significant reduction in BMI was identified (10 studies, <i>n</i> = 633; SMD = -0.50; 95% CI: -0.91 to -0.09; I² = 84%), and a small but significant effect on fat mass/body fat percentage was observed (8 studies, <i>n</i> = 479; SMD = -0.34; 95% CI: -0.62 to -0.06; I² = 57%). In sensitivity analyses excluding a study with pre-randomization baseline imbalance, the BMI effect attenuated to borderline significance (SMD = -0.45; <i>p</i> = 0.048) and the fat mass/body fat percentage effect lost statistical significance (SMD = -0.26; <i>p</i> = 0.060).[Conclusion] Short-term (8-12 weeks) probiotic/synbiotic supplementation may yield modest benefits on BMI and adiposity-related outcomes; however, sensitivity analyses indicated these effects were not robust to single-study exclusion. Body weight and lean body mass were not significantly affected. Use of post-intervention endpoint values (change-from-baseline scores were not consistently available) may have biased pooled estimates. Findings should be interpreted as preliminary.