Which hormone signals fullness and reduces appetite by acting on the hypothalamus?

• A. Ghrelin
• B. Neuropeptide Y
• C. Insulin
• D. Leptin

Answer: (D)

Leptin is the hormone that signals fullness to the brain. Produced by fat cells, it rises with energy stores and travels to the hypothalamus, where it binds receptors and reduces appetite. It helps curb hunger by dampening hunger-promoting signals and promoting fullness signals, supporting long-term energy balance. Some people can develop leptin resistance, which blunts this signal even when fat stores are high. By contrast, ghrelin increases appetite, neuropeptide Y promotes eating signals within the hypothalamus, and insulin also contributes to satiety but leptin specifically communicates stored energy status to reduce intake.