FGF19 triggers the brain to burn more energy and activate fat-burning cells, offering a potential new path for obesity treatments. The hormone enhances thermogenesis and reduces inflammation, but only when the sympathetic nervous system is active. Researchers uncovered how cold exposure increases receptor expression for FGF19 in the hypothalamus, hinting at an evolutionary role in temperature regulation. Ongoing work aims to discover how to boost natural production of this powerful metabolic hormone.