Research summary
Probiotics and Weight
Pooled analyses of randomized controlled trials suggest probiotic supplementation may be associated with a small reduction in body weight in overweight or obese adults over short intervention periods, but effects on BMI are mixed and the overall evidence is limited by small effect sizes, statistical heterogeneity, and short trial durations.[1], [2]
What the meta-analyses measured
Two systematic reviews with meta-analyses have pooled randomized controlled trials of oral probiotic supplementation in adults with overweight or obesity. One combined 15 trials (957 subjects) with intervention durations of 3 to 12 weeks; the other combined 8 trials (412 obese patients). Both reported a statistically significant reduction in body weight in the probiotic groups compared with placebo or control. In the larger analysis the average difference was about -0.60 kg, and the authors described the effect size as small.[1], [2]
Mixed signals on BMI and body composition
Findings for body mass index were inconsistent across the two analyses. One meta-analysis reported a small but significant reduction in BMI (about -0.27 kg/m2) and in fat percentage, while finding no significant effect on fat mass. The other reported no significant difference in BMI between probiotic and control groups, even though it did find significant reductions in body weight, waist circumference, and visceral fat content. Taken together, the data point to a modest and uneven picture rather than a uniform body-composition effect.[1], [2]
Why the evidence remains limited
Several factors temper how much these results can support. Effect sizes were small where present, statistical heterogeneity between trials was substantial for some outcomes, and most interventions lasted only a few weeks. The trials also used different probiotic strains, doses, and populations. As a result, the longer-term relevance of probiotics for body weight is uncertain, and the authors of both analyses called for additional randomized trials before firmer conclusions can be drawn.[1], [2]
Limitations of the evidence
The available meta-analyses pool relatively small, short randomized trials with varied probiotic formulations and report small, sometimes inconsistent effects on body weight and BMI. High between-study heterogeneity for some outcomes and intervention durations of only weeks limit confidence and say little about sustained weight change. This information is educational and not medical advice; individuals considering probiotics for weight should consult a qualified health professional.[1], [2]
References
- Effects of probiotics on body weight, body mass index, fat mass and fat percentage in subjects with overweight or obesity: a systematic review and meta-analysis of randomized controlled trials.. Obesity reviews : an official journal of the International Association for the Study of Obesity. 2018. Systematic review and meta-analysis View source →
- Effects of oral supplementation of probiotics on body weight and visceral fat in obese patients: a meta-analysis and systematic review.. Scientific reports. 2025. Systematic review and meta-analysis View source →