Leptin is a hormone produced by fat cells in the body. It plays a crucial role in regulating energy balance by signaling the brain about the body's fat stores. When fat stores are sufficient, leptin levels increase, which helps suppress appetite and promote energy expenditure. Conversely, when fat stores are low, leptin levels decrease, leading to increased hunger and reduced energy use. Leptin is often referred to as the "satiety hormone" because it helps control feelings of fullness. It works in conjunction with other hormones and signals to maintain a healthy weight and energy balance, influencing metabolism and overall health.