Leptin and Ghrelin in Appetite

Leptin and ghrelin are two hormones that act like a tug-of-war over your appetite, each pulling in the opposite direction. Ghrelin is the hunger signal: it is released mainly by an empty stomach, travels through the blood to the brain, and says "time to eat." Leptin is the fullness signal: it is made by your fat cells, and the more fat you store, the more leptin they release, telling the brain "we have enough energy stored, you can stop eating." Together they help your body keep its fuel tank from running too low or overflowing.

Both hormones report to the same control center deep in the brain — a small region called the hypothalamus that manages hunger, body temperature, and other automatic needs. There, ghrelin switches on the nerve cells that make you feel hungry, while leptin quiets them and switches on the cells that make you feel satisfied. This is why a hot meal can melt away hunger within minutes, and why going a long time without food makes the urge to eat grow stronger. When this signaling drifts out of balance — for example, when the brain stops responding well to leptin, a state called leptin resistance — the body can keep feeling hungry even with plenty of energy in reserve, which is one piece of the puzzle in obesity and weight regulation.