Leptin is a protein-like hormone secreted by adipocytes that regulates energy balance by suppressing hunger. In addition to white adipose tissue, which secretes leptin, brown fat, placenta, ovaries, skeletal muscle, stomach, breast epithelial cells, bone marrow, and P/D1 cells also produce leptin. Both leptin and the hunger hormone act on receptors in the arcuate nucleus of the hypothalamus as a means of regulating appetite and obtaining energy balance. The basic function of leptin is to regulate fat storage, but it also plays a role in other physiological and metabolic processes, yet many other functions remain undefined. Studies have linked leptin to obesity and weight loss.