French researchers pointed to a need to shore up the composition of the gut's microbiota ecosystem before or during bariatric surgery after they found persistent decreased microbial richness in severely obese patients.

The study found that both adjustable gastric banding and Roux-en-Y-gastric bypass improved microbial gene richness, but that microbial abundance was only partly restored in the majority of patients. Most had persistently low richness despite major metabolic improvement and weight loss, reported Karine Clement, MD, PhD, of Pitié-Salpêtrière Hospital in Paris, and colleagues in Gut.

"The lack of full rescue post-bariatric surgery calls for additional strategies to improve the gut microbiota ecosystem and microbiome-host interactions in severe obesity," the team wrote, suggesting that specialized diets, prebiotics, probiotics, or gut microbiota transfers before or after bariatric surgery might further improve microbial gene richness and metabolic health in severely obese individuals.

Obesity is associated with considerable microbial dysbiosis and metabolic complications. The authors said that their study is the first to assess this association in severely obese patients. While earlier studies showed changes in the gut microbiota, none explored microbial gene richness plus related metagenomics and metabolomic signatures after 6 months of follow-up.

The researchers enrolled 61 severely obese female patients from the hospital's obesity unit who had a body-mass index of 35 or higher and a mean age of approximately 39. Very low gene richness was present in 75% of severely obese patients, compared with previous research findings of 23% in the general population and 40% in overweight or mildly obese individuals.

In the Clement et al study cohort, 20 patients underwent adjustable gastric banding and 41 had Roux-en-Y gastric bypass. Seeking to determine how surgery would impact intestinal dysbiosis, the researchers followed 24 patients at 1, 3, and 12 months, analyzing fecal samples, gut microbiota, and serum metabolome; these were then compared with two other severely obese cohorts and an overweight/moderately obese cohort, as well as with lean individuals.

Low gene richness correlated with alterations in 78 metagenomic microbial species, 50% of which were associated with adverse body composition, adipocyte hypertrophy, and metabolic phenotypes.

Specifically, impoverished richness was inversely associated with the following metabolic indicators: triglycerides (P=0.049); uricemia (an indirect marker of insulin resistance, P=0.038); systemic inflammation markers fibrinogen (P=0.048); and neutrophil count (P=0.042) In addition, a low gene count inversely correlated with detrimental body composition (trunk-fat mass [r= –0.27, P=0.04]) and was significantly decreased in patients with type 2 diabetes (P=0.014) compared with in normoglycemic patients.

"It remains unknown whether this low microbial gene richness is a cause or consequence of obesity and of its duration, but it represents a good biomarker of gut microbiota alteration, [and may be] eventually useful for patient stratification," Clement and associates wrote.

While gastric banding increased microbial gene richness 1 year post-surgery, that factor remained low in Roux-en-Y patients, even though they showed greater metabolic improvement than banding patients. In bypass patients, clusters of metabolites such as glycine, acetylglycine, and methylmalonate increased in conjunction with reduced adipocyte size and body corpulence.

Last year, MedPage Today reported on a small study that found that gastric bypass but not banding improved the gut microbiome.

Clement et al acknowledged that the novel associations observed between microbial genetic richness, metabolites, and clinical phenotypes need testing in laboratory and murine models. In addition, there was a lack of data on the patients' food intake post-surgery.