Longitudinal changes of microbiome composition and microbial metabolomics after surgical weight loss in individuals with obesity

Background Some of the metabolic effects of bariatric surgery may be mediated by the gut microbiome. Objectives To study the effect of bariatric surgery on changes to gut microbiota composition and bacterial pathways, and their relation to metabolic parameters after bariatric surgery. Settings University hospitals in the United States and Spain. Methods Microbial diversity and composition by 16 S rRNA sequencing, putative bacterial pathways, and targeted circulating metabolites were studied in 26 individuals with severe obesity, with and without type 2 diabetes, before and at 3, 6, and 12 months after either gastric bypass or sleeve gastrectomy. Results Bariatric surgery tended to increase alpha diversity, and significantly altered beta diversity, microbiota composition, and function up to 6 months after surgery, but these changes tend to regress to presurgery levels by 12 months. Twelve of 15 bacterial pathways enriched after surgery also regressed to presurgery levels at 12 months. Network analysis identified groups of bacteria significantly correlated with levels of circulating metabolites over time. There were no differences between study sites, surgery type, or diabetes status in terms of microbial diversity and composition at baseline and after surgery. Conclusions The association among changes in microbiome with decreased circulating biomarkers of inflammation, increased bile acids, and products of choline metabolism and other bacterial pathways suggest that the microbiome partially mediates improvement of metabolism during the first year after bariatric surgery.