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 .
Bile acids synthesis decreases after laparoscopic sleeve gastrectomy.
BACKGROUND Bariatric surgery is the most effective treatment alternative in morbid obesity . The mechanisms contributing to these benefits remain poorly understood . Bile acids ( BAs ) are mediators of different regulatory functions in glucose and cholesterol homeostasis and energy expenditure . Recent evidence suggests that BAs are critically important for the beneficial effects of sleeve gastrectomy ( SG ) . OBJECTIVES The aim of this study was to evaluate the effect of SG on BA synthesis . SETTING University Hospital . Santiago , Chile . METHODS Obese patients were evaluated before and after SG ( 1 , 3 , 6 , and 12 months ) . BA synthesis was evaluated through the serum marker , 7 α-hydroxy-4-cholesten-3-one ( C4 ) . Primary and secondary BA and C4 were determined by high performance liquid chromatography coupled with t and em mass spectrometry detection ( HPLC-MS/MS ) . RESULTS From June 2013 to January 2014 , 19 patients ( age 37.6±7.8 years ; BMI 35.8±3.5 kg/m(2 ) ; 79 % female ) were included in this study . Mean weight loss at 1 , 3 , 6 , and 12 months was 11.3 , 17.5 , 23.6 , and 25.4 kg , respectively , equivalent to 11.8 , 18.6 , 24.8 , and 26.9 of total body water percentage ( % TBW ) ( P<.0001 ) , respectively and 43.2 , 68.2 , 91 , and 98.8 of percentage of excess weight loss ( % EWL ) , respectively ( P<.001 ) . Serum C4 levels at baseline , 1 , 3 , 6 , and 12 months were 23.4±21.1 , 4.9±8.2 , 8.7±12.1 , 13.8±12.9 , and 18.8±16.8 ng/mL ( P<.0001 ) , respectively . Fibroblast growth factor 19 ( FGF19 ) levels at baseline , 1 , 3 , 6 , and 12 months were 71±33.3 , 130.5±66.2 , 117.8±57.2 , 134.6±91.7 , and 124.3±85.9 pg/mL ( P = .019 ) , respectively . CONCLUSION Serum levels of C4 decrease after SG , indicating a reduction in the synthesis of BA . FGF19 may play a role in decreasing BA synthesis . Further studies are necessary to characterize the effect of bariatric surgery on BA homeostasis
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 .