Which hormone signals energy stores and reduces hunger?

• A. Ghrelin
• B. Peptide YY
• C. Leptin
• D. Insulin

Answer: (C)

Leptin serves as the long-term signal of the body's energy stores. It is released by fat tissue in proportion to how much fat is stored, then travels to the brain and tells the hypothalamus that energy reserves are sufficient. In response, hunger decreases and energy expenditure can increase, helping to maintain a stable weight over time. This makes leptin the primary hormone that links stored energy to appetite regulation.

Ghrelin, by contrast, comes from the stomach and rises when the stomach is empty, promoting hunger. Peptide YY is released after meals from the gut and helps suppress appetite, but it mostly reflects recent food intake rather than overall fat stores. Insulin signals the presence of available glucose and also can dampen hunger, but its main role is managing blood sugar, not indicating long-term energy reserves like leptin.