In addition to regulating the secretion and absorption of cholesterol, triglycerides, and fat-soluble vitamins, bile acids also function as signaling molecules to improve metabolism and play an anti-obesity role by activating the G-protein-coupled receptor 5 (TGR5) and Farnesoid X receptor (FXR). The gene discussed is XCR1; the disease is obesity due to melanocortin 4 receptor deficiency.