Circulating fasting total BA was not associated with obesity .
FGF19 was inversely and faecal BA excretion was positively associated with obesity .
Roux-en-Y gastric bypass ( RYGB ) and sleeve gastrectomy ( SG )  modulated BA metabolism , ie , increased BA and FGF19 .
Our results indicate that BA metabolism is altered in obesity .
Roux-en-Y Gastric Bypass and Vertical Banded Gastroplasty Induce Long-Term Changes on the Human Gut Microbiome Contributing to Fat Mass Regulation
Summary Bariatric surgery is currently the most effective procedure for the treatment of obesity . Given the role of the gut microbiota in regulating host metabolism and adiposity , we investigated the long-term effects of bariatric surgery on the microbiome of patients r and omized to Roux-en-Y gastric bypass or vertical b and ed gastroplasty and matched for weight and fat mass loss . The two surgical procedures induced similar and durable changes on the gut microbiome that were not dependent on body mass index and result ed in altered levels of fecal and circulating metabolites compared with obese controls . By colonizing germ-free mice with stools from the patients , we demonstrated that the surgically altered microbiota promoted reduced fat deposition in recipient mice . These mice also had a lower respiratory quotient , indicating decreased utilization of carbohydrates as fuel . Our results suggest that the gut microbiota may play a direct role in the reduction of adiposity observed after bariatric surgery
Circulating fasting total BA was not associated with obesity .
FGF19 was inversely and faecal BA excretion was positively associated with obesity .
Roux-en-Y gastric bypass ( RYGB ) and sleeve gastrectomy ( SG )  modulated BA metabolism , ie , increased BA and FGF19 .
Our results indicate that BA metabolism is altered in obesity .