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 .
Weight loss induced by Roux-en-Y gastric bypass but not laparoscopic adjustable gastric banding increases circulating bile acids.
CONTEXT It has been hypothesized that increased plasma bile acids ( BAs ) contribute to metabolic improvements after Roux-en-Y gastric bypass ( RYGB ) surgery by the G protein-coupled receptor TGR5-mediated effects on glucagon-like peptide-1 secretion and thyroid hormones . OBJECTIVE The objective of this study was to evaluate the importance of bariatric surgery-induced alterations in BA physiology on factors that regulate glucose homeostasis ( insulin secretion and sensitivity ) and energy metabolism ( resting energy expenditure and thyroid hormone axis ) . DESIGN , PARTICIPANTS , INTERVENTION , AND MAIN OUTCOME MEASURE : Eighteen extremely obese subjects were studied before and after 20 % weight loss , induced by either laparoscopic adjustable gastric b and ing ( LAGB ) ( n = 10 ) or RYGB surgery ( n = 8) . RESULTS Plasma BAs more than doubled after RYGB [ fasting : 1.08 ( 0.26 - 1.42 ) to 2.28 ( 1.59 - 3.28 ) μmol/L , P = .03 ; postpr and ial : 2.46 ± 1.59 to 6.00 ± 2.75 μmol/L , P = .01 ] but were either lower or did not change after LAGB [ fasting : 1.80 ( 1.49 - 2.19 ) to 0.92 ( 0.73 - 1.15 ) μmol/L , P = .02 ; postpr and ial : 3.71 ± 2.61 to 2.82 ± 1.75 μmol/L , P = .14 ] . Skeletal muscle expression of TGR5 targets , Kir6.2 and cyclooxygenase IV , increased after RYGB but not LAGB . Surgery-induced changes in BAs were associated with increased peak postpr and ial plasma glucagon-like peptide-1 ( r(2 ) = 0.509 , P = .001 ) and decreased serum TSH ( r(2 ) = 0.562 , P < .001 ) but did not correlate with the change in insulin response to a meal ( r(2 ) = 0.013 , P = .658 ) , insulin sensitivity ( assessed as insulin stimulated glucose disposal during a hyperinsulinemic-euglycemic clamp procedure ) ( r(2 ) = 0.001 , P = .995 ) , or resting energy expenditure ( r(2 ) = 0.004 , P = .807 ) . CONCLUSIONS Compared with LAGB , RYGB increases circulating BAs and TGR5 signaling , but this increase in BAs is not a significant predictor of changes in glucose homeostasis or energy metabolism
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 .