FMT Doesn’t Appear to Affect Weight Loss After Bariatric Surgery

Fecal microbiota transplantation (FMT) does not appear to contribute to weight loss for patients who undergo bariatric surgery, according to results of a randomized controlled trial conducted in Finland.

The small study by Perttu Lahtinen, MD, with Päijät-Häme Central Hospital in Lahti, and colleagues was published online in JAMA Network Open.

Bariatric surgery remains the most effective strategy for treating severe obesity. Yet some patients achieve only minimal weight loss or regain weight after surgery, the researchers note.

There is much interest in the gut microbiota as a potential target for the treatment of obesity. FMT from a lean donor has shown promise in treating obesity in mouse models.

But the Finnish trial does not support that conclusion.

The study included 41 adults (71% women; mean age, 48.7 years) with severe obesity (mean body mass index, 42.5). Twenty-one received FMT from a lean donor, and 20 received FMT from their own feces (autologous placebo). FMT was administered by gastroscopy into the duodenum 6 months before laparoscopic Roux-en-Y gastric bypass or sleeve gastrectomy. All patients also consumed a very-low-calorie diet approximately 4 weeks before the surgery.

Bariatric surgery led to equal weight reductions for both groups, but there was no additive benefit in terms of weight loss with FMT.

Six months after the administration of FMT, and before the surgery was performed, the percentage of total weight loss, the main outcome, was 4.8% (P < .001) in the FMT group and 4.6% (P = .006) in the placebo group. There was no statistically significant difference between the groups (absolute difference, 0.2%).

At 18 months (12 months after surgery), the percentage of total weight loss was 25.3% (P < .001) in the FMT group and 25.2% (P < .001) in the placebo group ― an absolute difference of 0.1%.

The researchers say the main limitation of their study is the small number of patients. Because there were few patients, the study may be inadequate to show possible minor effects of FMT on weight; it’s unclear whether a much larger sample size would have yielded any differences between the groups, they add.

Nonetheless, the study suggests that FMT does not affect weight loss for patients who undergo bariatric surgery, the researchers say.

The study was supported by governmental research grants and the Sigrid Juselius Foundation. The authors have disclosed no relevant financial relationships.

JAMA Netw Open. Published online December 16, 2022. Full text

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