Definition
Ghrelin is a hormone produced primarily in the stomach. It's often referred to as the 'hunger hormone' because it stimulates appetite. Ghrelin levels rise when your stomach is empty. It signals your brain that it's time to eat. Think of ghrelin as your body's personal food alarm. It reminds you to refuel when your energy stores are low. Ghrelin also plays a role in regulating sleep-wake cycles.