Jeffrey Friedman investigates the physiologic and neural mechanisms that regulate food intake and body weight. Specifically, Friedman and his team identified and study leptin, a hormone made by fat tissue that acts on the brain and is the afferent signal in a feedback loop maintaining body weight. They have found that leptin regulates glucose metabolism and numerous other physiologic systems. While uncommon in humans, leptin mutations cause extreme obesity and leptin treatment dramatically reduces weight in these patients and in mice. The team explores the neural mechanisms by which leptin acts on the brain to mediate its effects, while also seeking to identify other key regulators of body weight.