leptin Hormone secreted by adipose tissue that acts to regulate long‐term appetite and energy expenditure by signalling the state of body fat reserves. Lack of leptin secretion is an extremely rare cause of obesity; most obese people secrete higher than normal amounts of leptin, but are less sensitive to its actions.

leptin (lep-tin) n. a protein, produced by adipose tissue, that has a role in regulating eating: an increase in adipose tissue results in higher concentrations of leptin, which reduce food intake.