Leptin is a hormone that regulates food intake and body weight, states News Medical. Leptin acts on specific receptors in the hypothalamus to inhibit appetite and reduce weight.
Leptin counteracts the effects of the appetite stimulatory hormone neuropeptide Y as well as the neurotransmitter adandamide that stimulates appetite, states News Medical. Leptin also promotes the synthesis of an appetite stimulant called alpha melanocyte-stimulating hormone.
Leptin regulates the size of fat cells in the body, according to News Medical. When there is less fat, the level of leptin decreases, and this stimulates appetite and reduces energy expenditure. When there is an increase in fat, the level of leptin increases. This suppresses appetite and increases energy expenditure, thus weight loss occurs. In this way, leptin regulates energy intake and fat stores, so that weight is maintained within a narrow range.
The absence of leptin in the body or leptin resistance can lead to uncontrolled food intake and weight gain, states News Medical. The absence of leptin or leptin resistance also prevents puberty. Therefore leptin plays a role in the regulation of the onset of puberty. Girls who are undernourished have little fat cells and very low levels of leptin, taking longer to reach puberty. These girls fail to release eggs from the ovary during the menstrual cycle.