"In the past 20 years, we've learned a lot about hunger and satiety hormones," says Scott Isaacs, MD, a board-certified endocrinologist in Atlanta and author of Beat Overeating Now! "The first one was leptin, which was discovered in 1994." Since then, many other hormones that impact hunger, appetite, cravings, and weight have been discovered.
"Leptin is a hormone that's produced by fat cells, and it works to suppress appetite in the brain," Isaacs explains. "We used to think a fat cell was an inert storage depot for excess fat, insulating the body. But now we know that fat is an endocrine organ, that is, a gland that produces hormones. Leptin is just one of the hormones produced by fat cells." The amount of leptin circulating in a person is proportional to the amount of body fat and indicates how much energy stores a person has.