Leptin is a recently discovered hormone. Jeffrey Friedman (1954-) and his colleagues published a paper in December 1994 announcing the discovery of a gene in mice and humans called obese (ob) that codes for a hormone he later named leptin, after the Greek word leptos, meaning “thin.” Leptin is a hormone made by the body’s adipose tissue that regulates food intake and energy expenditure. Individuals who lack leptin eat tremendous amounts of food and become obese.