Effects of Probiotic and Synbiotic Supplementation on Body Composition and Glucose Metabolism in Children and Adolescents with Overweight or Obesity: A Systematic Review and Meta-Analysis

Background/Objectives: Childhood and adolescent overweight and obesity are associated with adverse body composition and impaired glucose metabolism. Probiotic and synbiotic supplementation may modulate the gut microbiota and has been proposed as a potential adjunctive strategy for obesity management. This systematic review and meta-analysis aimed to evaluate the effects of probiotic and synbiotic supplementation on body composition and glucose metabolism in children and adolescents with overweight or obesity. Methods: This review was conducted according to the PRISMA 2020 statement. PubMed, Embase, Web of Science, the Cochrane Library, and CNKI were searched from inception to 5 May 2026. Randomized controlled trials evaluating probiotic or synbiotic supplementation in children and adolescents with overweight or obesity were included. Outcomes included BMI z-score, BMI, waist circumference, body fat percentage, fasting glucose, fasting insulin, and HOMA-IR. Random-effects meta-analyses, sensitivity analyses, and subgroup analyses according to intervention type (probiotic versus synbiotic supplementation) were performed using mean differences (MDs) and 95% confidence intervals (CIs). Risk of bias was assessed using RoB 2, and certainty of evidence was evaluated using GRADE. Results: Sixteen randomized controlled trials were included. Probiotic or synbiotic supplementation did not significantly reduce BMI z-score (MD = −0.03, 95% CI −0.11 to 0.05), waist circumference (MD = 0.60 cm, 95% CI −1.57 to 2.77), or body fat percentage (MD = −0.29 percentage points, 95% CI −1.64 to 1.06). A modest reduction in BMI was observed (MD = −0.91 kg/m2, 95% CI −1.81 to −0.01), although this finding should be interpreted cautiously because no significant improvement was observed in BMI z-score. No significant effects were found for fasting glucose, fasting insulin, or HOMA-IR. Subgroup analyses showed no significant differences between probiotic and synbiotic supplementation for BMI, BMI z-score, or waist circumference, whereas a significant subgroup difference was observed for fasting glucose. Conclusions: Probiotic or synbiotic supplementation may be associated with a modest reduction in BMI; however, the certainty of this evidence was low, which limits confidence in its clinical implications. Current evidence does not support clear benefits for BMI z-score, waist circumference, body fat percentage, or glucose metabolism. The subgroup findings, particularly for fasting glucose, should be interpreted cautiously because they were based on a limited number of studies. Further high-quality randomized controlled trials are warranted.