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Fecal microbiota transplantation (FMT) had no effect on weight loss, body composition, or metabolic markers in obese individuals who underwent bariatric surgery, said authors of a small clinical trial.

In 41 adults with severe obesity, total weight loss at 12 months post-surgery was not significantly different in those who received FMT beforehand compared with those who received a placebo transplant (25.3% vs 25.2%, P=0.99), Perttu Lahtinen, MD, of Päijät-Häme Central Hospital in Lahti, Finland, and colleagues reported in .

Both groups experienced similar reductions in body-mass index (BMI), high-density lipoprotein cholesterol, triglycerides, fasting glucose, and other metabolic markers. Furthermore, quality-of-life assessments did not differ significantly between the two groups, the study found.

A in mice suggested FMT might be effective in treating obesity, the researchers noted. "The intestinal microbiota has aroused interest as a potential target for the treatment of obesity. Most patients with severe obesity harbor an intestinal microbiota with decreased bacterial diversity and microbial gene richness compared with healthy controls."

"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 team added.

The randomized, double-blind, placebo-controlled trial included 41 adults with a mean BMI of 42.5. Their mean age was 48.7, and nearly three-quarters (71%) were women. Twenty-one patients received FMT from a lean donor, and 20 received a placebo transplant of their own fecal microbiota -- both groups by gastroscopy into the duodenum.

The fecal transplants were obtained from two lean individuals with healthy lifestyles: a donor in their 40s who practiced long-distance training (BMI <20), and another in their 50s who was an organic gardener (BMI <25). Both donors were omnivores; were generally healthy, without diagnosed chronic diseases or medications; and had not used antibiotics within the preceding 12 months.

The transplants were conducted 6 months before the patients underwent bariatric surgery with laparoscopic Roux-en-Y gastric bypass or laparoscopic sleeve gastrectomy. The main outcome was weight reduction measured as the percentage of total weight loss. Secondary outcomes included changes in body composition, lipid levels, and glucose control.

Assessments of body composition 12 months after surgery did not differ significantly between the two groups:

• Reduction in mean BMI: 10.4 in the FMT group, 10.15 in the placebo group

• Decrease in mean fat content: 8.8% in the FMT group, 7.6% in the placebo group

• Decrease in mean visceral fat content: 6.9% in the FMT group, 5.3% in the placebo group

• Decrease in mean muscle mass: 8.0 kg in the FMT group, 9.9 kg in the placebo group

Previous studies of FMT in obese individuals also reported minimal effects on body weight, Lahtinen and co-authors noted, adding, however, that some of these studies reported slight improvements in insulin sensitivity, abdominal adiposity, and lipid metabolism.

For example, a randomized, placebo-controlled that included obese adolescents ages 14 to 18 reported significant changes in the android-to-gynoid fat ratio in the FMT versus the placebo group at 26 weeks (−0.029, 95% CI −0.049 to −0.008). The intervention in this study was a single course of oral encapsulated fecal microbiome from healthy lean donors of the same sex or saline placebo.

A chief limitation of the current study was the small sample size, which may have been inadequate to show small differences in weight loss related to FMT, the researchers noted. "In the absence of published data, our estimation of the treatment effect was optimistic, and, thus, the number of patients was tuned to detect only clear differences between the groups."

"Limited numbers of patients may generate a type II error," the team explained, "and we were unable to determine whether a much larger sample size would have yielded any differences between the groups according to these results."

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