Fibroblast growth factor 19 (FGF-19) is a protein that in humans is encoded by the FGF19 gene. FGF-19 regulates new bile acid synthesis, acting through the FGFR4/Klotho-β receptor complexes in the liver to inhibit CYP7A1. FGF-19 also has metabolic effects, affecting glucose and lipid metabolism when used in experimental mouse models. Patients with chronic diarrhea due to bile acid malabsorption have been shown to have reduced fasting FGF-19. FGF-19 is also found in the liver of patients with cholestasis. Patients with the metabolic syndrome, non-alcoholic fatty liver disease and insulin resistance have reduced levels of FGF-19. FGF-19 increases to normal values in obese patients who undergo Roux-en-Y gastric bypass bariatric surgery.