Ghrelin is known as the "hunger hormone" because it is produced primarily by the stomach and signals the hypothalamus to stimulate appetite. It increases food intake by promoting hunger sensations, especially during fasting or before meals. Ghrelin levels rise preprandially and decline after eating, directly influencing energy balance. Unlike leptin, insulin, or glucagon, ghrelin acts centrally to trigger hunger and meal initiation. This regulatory role makes it a key hormone in the control of food intake and body weight.

Reference: Principles of Surgery, Schwartz SI, 11th Edition.