Context: Bile acids and fibroblast growth factor 19 (FGF19) have been suggested as key mediators of the improvements in glucose metabolism after Roux-en-Y gastric bypass (RYGB).

Objective: To describe fasting and postprandial state total bile acid (TBA) and FGF19 concentrations before and after RYGB and relate them to parameters of glucose metabolism, glucagon-like peptide-1, cholecystokinin, and cholesterol fractions.

Design and Setting: A prospective descriptive study was performed at the Department of Endocrinology, Hvidovre Hospital, Hvidovre, Denmark.

Patients: Thirteen type 2 diabetic (T2D) patients and 12 normal glucose tolerant (NGT) subjects participated in the study.

Intervention: A 4-hour liquid meal test was performed before and 1 week, 3 months, and 1 year after RYGB.

Main Outcome Measures: We measured fasting and postprandial TBA and FGF19 concentrations.

Results: Fasting TBA concentrations decreased in NGT subjects (P < .001) and were unchanged in T2D patients 1 week after surgery, but then increased gradually in both groups with time from surgery (ANOVA Ptime < .001). Area under the curve (AUC) TBA was decreased in NGT subjects 1 week after RYGB (before surgery, 567 mmol * min/L [interquartile range, 481–826]; 1 wk, 419 [381–508]; P = .009) and was unchanged in T2D patients (894 [573–1002]; 695 [349–1147]; P = .97) but then increased with time from surgery in both groups (Ptime < .001). Fasting FGF19 concentrations were unchanged acutely after RYGB (NGT, 140 pg/mL [100–162], 134 [119–204], P = .42; T2D, 162 [130–196], 154 [104–164], P = .68) and remained unchanged throughout the follow-up period. AUC FGF19 increased gradually with time after surgery (Ptime < .001), resembling the changes seen with AUC TBA. One week after RYGB, glucose metabolism improved, low-density lipoprotein-cholesterol and high-density lipoprotein-cholesterol decreased, and cholecystokinin and glucagon-like peptide-1 secretion increased, whereas FFA concentrations were unchanged.

Conclusion: TBA and FGF19 do not explain acute changes in glucose metabolism, cholesterol fractions, and gut hormone secretion after RYGB.