Fibroblast growth factor 19 (FGF-19) is encoded by the FGF-19 gene in humans. FGF-19 regulates the synthesis of bile acids through FGFR4/Klotho in the liver- β The receptor complex has an inhibitory effect on CYP7A1. It was found in mouse models that FGF-19 also has metabolic effects, which can affect glucose and lipid metabolism. FGF-19 is reduced in patients with chronic diarrhea due to bile acid absorption disorders. FGF-19 is also present in the liver of patients with bile stasis. The expression of FGF-19 is reduced in patients with metabolic syndrome, non-alcoholic fatty liver disease, and insulin resistance. Obese patients who underwent Roux en Y gastric bypass surgery for weight loss showed an increase in FGF-19 to normal levels.