The hormone leptin is associated with the regulation of body weight and the normal maintenance of bodily functions (homeostasis). It is found in fat cell (adipocyes) and communicates the nutritional status of the body to the brain (central nervous system). Research using animals has shown that defects in the communication between leptin and the brain causes obesity (the state of being overweight). It has also been noted that obese humans tend to have high levels of leptin.