Study overview
This is a randomized, double-masked, placebo-controlled trial studying Fecal Microbiota Transplantation (FMT) or placebo in 87 randomized adolescents aged 14 to 18 years with Adiposity / Obesity (body mass index of 30 or more) (1).
Primary outcome measures
BMI standard deviation score at 6 weeks using intention-to-treat analysis (1)
Results (1)
- BMI Standard Deviation Score: There was no significant effect of FMT on the BMI standard deviation score at 6 weeks, with an adjusted mean difference (aMD) of −0.026 (95% CI: −0.074, 0.022).
- Fat Distribution: Reductions in the android-to-gynoid fat ratio were observed in the FMT group compared to the placebo group at 6, 12, and 26 weeks. The aMDs were:
- 6 weeks: −0.021 (95% CI: −0.041 to −0.001)
- 12 weeks: −0.023 (95% CI: −0.043 to −0.003)
- 26 weeks: −0.029 (95% CI: −0.049 to −0.008)
- Other Health Metrics: No effects were observed on insulin sensitivity, liver function, lipid profile, inflammatory markers, blood pressure, total body fat percentage, gut health, or health-related quality of life.
- Gut Microbiome: Profiling indicated a shift in community composition among the FMT group, which was maintained up to 12 weeks.
- Metabolic Syndrome: In post-hoc exploratory analyses, among participants with metabolic syndrome at baseline, FMT led to a greater resolution of the condition (from 18 to 4 participants) compared to placebo (from 13 to 10 participants) by 26 weeks. The adjusted odds ratio was 0.06 (95% CI: 0.01-0.45; P = .007).
No serious adverse events were recorded throughout the trial.
Conclusion
In this randomized clinical trial involving adolescents with obesity, FMT did not affect weight loss, but a reduction in abdominal adiposity was noted (1). A 2025, unblinded four-year follow-up of Gut Bugs participants reported smaller waist circumference and lower body-fat percentage in the FMT group, but no statistically significant BMI difference. Only 55 of the original 87 participants returned, so this is an encouraging signal that needs confirmation—not definitive evidence of lasting benefit (2).
References
(1) Leong et al. 2020 JAMA Netw Open 3(12): e2030415
(2) Wilson et al. 2025 Nat Commun 16: 7786
