Fecal Microbiota Transplantation (FMT) & Adiposity / Obesity

Why Use Fecal Microbiota Transplantation (FMT) for Adiposity / Obesity
Fecal Microbiota Transplantation (FMT) is being studied as a way to test whether changing the gut microbial community can affect adiposity and metabolic health - not only body weight. This approach is based on the possibility that gut microbes influence how the body extracts and stores energy and regulates metabolism. Supporting this rationale, animal-transfer experiments found that microbiota from obese donors increased fat gain in germ-free mice compared with microbiota from lean donors (7, 8); these findings support the broader rationale for FMT research (5, 6).

Fecal Microbiota Transplantation (FMT) for Adiposity / Obesity: Reviews And Meta-Analyses

• Zhang et al., 2019 - systematic review (3 RCTs; 76 adults). Small, short trials (2–18 weeks; participants were men with obesity/metabolic syndrome) showed mixed metabolic findings. Two reported improved peripheral insulin sensitivity at 6 weeks and one reported lower HbA1c; BMI, fasting glucose, hepatic insulin sensitivity, and lipid markers did not consistently improve. The authors did not pool results because the small, incomplete datasets made a pooled estimate of limited value (13).


• Hu et al., 2023 — meta-analysis/comprehensive assessment (6 publications; 130 participants). Reported lower weight after FMT than at baseline (WMD −4.77 kg) and favorable pre/post glycaemic findings. Interpret this cautiously: a pre/post change is not the same as a controlled between-group treatment effect, and the included studies/populations were small and mixed (14).


• Zecheng et al., 2023 — RCT meta-analysis (10 studies; 334 participants). Reported favorable associations for several cardiometabolic variables, but the abstract also reports mixed directions for some outcomes. The small, overlapping trial base and variation in outcomes/comparators limit inference about a specific anti-obesity effect (15).


• Zhang et al., 2025 — obesity/metabolic-disorders systematic review and meta-analysis (11 RCTs; 320 analyzed participants). Primary analyses did not reach statistical significance: BMI, 5 trials/107 participants, MD −0.65 (95% CI −1.35 to 0.05; p=0.070); HOMA-IR, 7/211, MD −0.64 (−1.31 to 0.03; p=0.062); HbA1c, 6/156, MD +0.06 (−0.29 to 0.40; p=0.742). Total cholesterol, LDL, HDL, and triglycerides also showed no significant pooled differences. All outcomes were rated low-certainty. The BMI result changed to statistically significant under an alternative assumption for estimating change-score variance (p=0.010), indicating analytic sensitivity rather than a robust finding (16).

Fecal Microbiota Transplantation (FMT) for Adiposity / Obesity: Randomized clinical trials (RCTs)

For the randomized basic science clinical trial NCT05607745, there are no published results as of March 2026
The randomized, double-masked, placebo-controlled trial ACTRN12615001351505 revealed that FMT did not affect weight loss, but a reduction in abdominal adiposity was noted (12). 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 (17).
For the randomized, double-blinded and placebo controlled clinical treatment trial NCT03273855, there is no yet publicly available full results article as of February 2026.
The randomized placebo-controlled clinical trial NCT03127696 demonstrated that repeated FMTs enhance both the level and duration of microbiota engraftment in obese patients with Type 2 Diabetes Mellitus (T2DM). When FMT is combined with lifestyle intervention, it leads to more favorable changes in the recipients' microbiota, along with improvements in lipid profile and liver stiffness (11).
The randomized clinical phase I/II treatment trial NCT02530385 revealed that adults with obesity, the weekly administration of FMT capsules led to the engraftment of gut microbiota in most participants for a duration of at least 12 weeks. However, despite this engraftment, the study did not reveal any clinically significant metabolic effects (1).
The randomized clinical phase I/II treatment trial NCT02741518 demonstrated that FMT capsules, which were derived from a lean donor, were safe for use. However, they did not result in a reduction of BMI in patients who were obese but metabolically uncompromised. The capsules were well tolerated by the participants and led to sustained alterations in the intestinal microbiome and bile acid profiles, which closely resembled those of the lean donor (10). Allegretti et al. (2021) report a possible improvement in post-meal glucose and insulin responses - but no weight loss or confirmed prevention of metabolic syndrome - in a secondary analysis of the same small study (NCT02741518) (9).”
For the randomized clinical phase II treatment trial NCT05253768, no published results found as of February 2026
For the randomized clinical phase II treatment trial NCT02970877, there is no yet publicly available full results article as of February 2026.

Fecal Microbiota Transplantation (FMT) for Adiposity / Obesity: Non-randomized clinical trials

For the non-randomized clinical treatment trial NCT03789461, no published results found as of March 2026

Fecal Microbiota Transplantation (FMT) for Adiposity / Obesity: Preclinical data

Fecal Microbiota Transplantation (FMT) (obtained before and four months after treatment) from metformin-treated donors to germ-free mice showed that Glucose tolerance / Oral glucose tolerance test (OGTT) was improved in mice that received metformin-altered microbiota (4).

Fecal Microbiota Transplantation (FMT) for Adiposity / Obesity: Conclusion

Fecal Microbiota Transplantation (FMT) remains investigational for adiposity/obesity. Human trials show that donor microbiota can engraft and alter microbiome composition, but this has not translated into a reproducible, clinically meaningful reduction in body weight or BMI. Meta-analyses report inconsistent short-term metabolic-marker signals; the most recent obesity-focused meta-analysis found no statistically significant primary effects on BMI, HOMA-IR, HbA1c, or lipids, and rated the evidence low certainty. A newer, broader metabolic-disorders review likewise found no robust glycaemic benefit and judged the evidence very low/low certainty. FMT should not be presented as an established weight-loss treatment; use for metabolic indications belongs in clinical research.

References

(1) Yu et al. 2020f
(2) Vrieze et al. 2012 Gastroenterology 143(4): 913-17
(3) Di Luccia et al. 2015 PLoS One 10: e0134893
(4) Wu et al. 2017 Nat Med 23: 850-8
(5) Turnbaugh et al. 2006 Nature 444: 1027-31
(6) Turnbaugh et al. 2008 Cell Host and Microbe 3: 213-223
(7) Ridaura et al. 2013 Science 341: 1241214
(8) Tremaroli et al. 2015 Cell Metab. 22:228–238
(9) Allegretti et al. 2021 Hormones 20: 209–211
(10) Allegretti et al. 2020 Clinical Gastroenterology and Hepatology 18(4): 855-863
(11) Ng et al. 2022 Gut 71(4): 716-723
(12) Leong et al. 2020 JAMA Netw Open 3(12): e2030415
(13) Zhang et al. 2019 Nutrients 11(10): 2291
(14) Hu et al. 2023 Life 13: 1488
(15) Zecheng et al. 2023 Diabetes Research and Clinical Practice 202: 110803
(16) Zhang et al. 2025 Frontiers in Endocrinology 16: 1737543
(17) Wilson et al. 2025 Nat Commun 16: 7786
see also:
Adiposity / Obesity & Drugs / Treatments
Application & Fecal Microbiota Transplantation (FMT)
Dysbiosis & Metabolic Syndrome (MetS)
Fecal Microbiota Transplantation (FMT) & Metabolic diseases / Metabolic disorders
Fecal Microbiota Transplantation (FMT) & Metabolic Syndrome (MetS)
Fecal Microbiota Transplantation (FMT) & Non-Alcoholic Fatty Liver Disease (NAFLD) / Metabolic dysfunction-associated fatty liver disease (MAFLD)
Fecal Microbiota Transplantation (FMT) + Lifestyle intervention (LSI) & Adiposity / Obesity
MET-3 & Adiposity / Obesity
Microbiome-based therapeutics & Adiposity / Obesity