Fecal microbiota transplantation (FMT) does not significantly increase the percentage of total weight lost before or after Roux-en-Y gastric bypass and laparoscopic sleeve gastrectomy among adults with severe obesity, according to study findings published in JAMA Network Open.

Researchers in Finland conducted a double-blind, placebo-controlled, multicenter, randomized clinical trial from January 2018 to March 2021 to assess whether FMT further promotes weight loss following bariatric surgery.

A total of 41 adults with obesity were randomly assigned to 2 treatment groups—21 received FMT from a lean donor (intervention) and 20 received an autologous FMT (placebo), both of which were administered via gastroscopy into the duodenum. Six months following FMT, 38 of the 41 individuals underwent bariatric surgery—34 via laparoscopic Roux-en-Y gastric bypass (RYGB) and 4 via laparoscopic sleeve gastrectomy (LSG).

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The researchers collected each patient’s weight and body mass index (BMI) at baseline and repeated these measurements along with calculating excess body mass index loss at 2, 4, 6, 9, 12, and 18 months after baseline. Only 34 of 41 patients (82.9%) completed the final 18-month follow-up after the initial visit.

At 6 months following FMT just prior to bariatric surgery, total weight loss averaged 4.8% in the true FMT group (95% CI, 2.7%-7.0%; P <.001) and 4.6% in the placebo group (95% CI, 1.5%-7.6%; P =.006). No differences were observed between the 2 groups at the 2- and 4-month time points either.

At 18 months, total weight loss increased to 25.3% among patients in the intervention group (95% CI, 19.5%-31.1%; P <.001) and 25.2% among those in the placebo group (95% 20.2%-30.3%; P <.001). Neither point in time resulted in significant differences between the 2 groups.

Study limitations include the small sample size and the possibility of type II error. Additionally, gut microbiota may have been altered by prophylactic antibiotics use and the possibility of microbiota change immediately after defecation despite short oxygen exposure.

“Our study provides further evidence that FMT alone is not sufficient to decrease body weight in humans. However, FMT may exert a transient effect on more delicate markers of metabolism,” the study authors conclude.

Disclosure: Multiple authors declared affiliations with industry. Please see the original reference for a full list of disclosures.


Lahtinen P, Juuti A, Luostarinen M, et al. Effectiveness of fecal microbiota transplantation for weight loss in patients with obesity undergoing bariatric surgery: A randomized clinical trialJAMA Netw Open. 2022;5(12):e2247226. doi:10.1001/jamanetworkopen.2022.47226

This article originally appeared on Gastroenterology Advisor