What Is Leptin? Leptin is a hormone produced by fat cells that communicates with the brain, particularly the hypothalamus, to signal that the body has sufficient energy stores. When this signaling works properly, appetite decreases and feelings of fullness increase. Because of this important role, leptin is often called the "satiety hormone." Why Are People with Obesity Still Hungry? People with obesity usually have higher leptin levels because they have more body fat. Howev