Which protein secreted by fat cells communicates about body fat stores to the brain?

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

Answer: (B)

Leptin is the signal produced by fat tissue that tells the brain how much body fat is stored. Adipose cells release leptin in proportion to fat mass, and it travels to receptors in the hypothalamus. When fat stores are high, leptin levels rise, signaling the brain to reduce appetite and increase energy expenditure, helping maintain energy balance. This makes leptin the correct choice as the long‑term regulator of fat stores communicating with the brain.

Ghrelin comes from the stomach and stimulates hunger, not the fat stores’ signal. Insulin reflects nutrient status and glucose metabolism but is produced by the pancreas, not fat cells, and its primary role isn’t reporting fat reserves to the brain. Neuropeptide Y is a brain-produced peptide that stimulates appetite rather than being secreted by fat tissue.