Summary Regional changes to the intestinal microenvironment brought about by Roux-en-Y gastric bypass (RYGB) surgery may contribute to some of its potent systemic metabolic benefits through favorably regulating various local cellular processes. Here, we show that the intestinal contents of RYGB-operated compared with sham-operated rats region-dependently confer superior glycemic control to recipient germ-free mice in association with suppression of endotoxemia. Correspondingly, they had direct barrier-stabilizing effects on an intestinal epithelial cell line which, bile-exposed intestinal contents, were partly farnesoid X receptor (FXR)-dependent. Further, circulating fibroblast growth factor 19 levels, a readout of intestinal FXR activation, negatively correlated with endotoxemia severity in longitudinal cohort of RYGB patients. These findings suggest that various host- and/or microbiota-derived luminal factors region-specifically and synergistically stabilize the intestinal epithelial barrier following RYGB through FXR signaling, which could potentially be leveraged to better treat endotoxemia-induced insulin resistance in obesity in a non-invasive and more targeted manner.

Roux‐en‐Y gastric bypass surgery (RYGB) provides superior long‐term glycaemic control in severely obese and insulin resistant individuals. The improved peripheral insulin sensitivity at later stages after RYGB has been attributed in part to a reduction in intestinal permeability and associated endotoxemia, but the underlying mechanisms remain unclear. Here, we used diet‐induced obese rat and Caco2 cell monolayer models to show that RYGB region‐specifically strengthens intestinal epithelial barrier (IEB) integrity. This was partly farnesoid X receptor (FXR)‐dependent for the bile‐exposed duodenum and colon but not for the bile‐excluded jejunum. Transfer experiments performed on recipient germ‐free mice additionally demonstrated that jejunal and colonic but duodenal content of RYGB‐operated rats contain microbiota‐produced factors which improve oral glucose tolerance in proportion to suppression in endotoxemia. Collectively, these findings suggest that luminal primary and secondary bile acids acting through FXR in duodenal and colonic epithelial cells respectively, contribute to overall strengthening of IEB integrity and improved glucose homeostasis after RYGB and further support the use of bile acid mimetics for the treatment of metabolic disease.