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 acid malabsorption after jejunoileal bypass is less compensated for with a 1:3 than with a 3:1 jejunoileal ratio.
A previous study surprisingly showed that after jejunoileal bypass a ratio of 1:3 compared with 3:1 between the jejunal and ileal segment left in continuity result ed in a smaller synthesis rate , pool size , and postcibal jejunal levels of bile acids . These findings are reevaluated in the present study of 34 patients who either were waiting for or 3 , 9 , or 15 months earlier , had undergone bypass surgery with a 3:1 or 1:3 jejunoileal ratio . Compared with 3:1 bypass , the 1:3 bypass result ed in ( i ) greater reduction of the fasting bile acid pool , significant for chenodeoxycholic acid but not for cholic adic , ( ii ) less increase in synthesis rate of both bile acids , ( iii ) less decrease in relative content of taurine-conjugated bile acids in bile , and ( iv ) equal reduction of postcibal levels of bile acids in jejunum . We conclude that the increase in synthesis of bile acids compensates insufficiently for the excess fecal loss ; the lower synthesis rate after bypass with a short jejunum relative to ileum in function may be due to an impaired stumulation of bile acid synthesis , the mechanism of which is unexplained
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 .