Ghrelin makes you hungry. Leptin helps tell your brain when you’ve had enough.

They work on different timelines, but together they help regulate appetite and body weight.

Ghrelin: the hunger signal

Levels typically rise when your stomach is empty and fall after you eat. Think of it as the signal that tells your brain, it’s probably time to eat.

It works relatively quickly and changes throughout the day based on meals, sleep, and other factors.

Leptin: the longer-term signal

Leptin is produced by fat cells, so levels generally reflect how much stored energy your body has available.

Rather than telling you whether you need lunch right now, leptin gives your brain a broader picture of your energy stores. When leptin signaling is working normally, it helps regulate appetite and energy use over time.

Your brain puts the signals together

Both hormones communicate with the hypothalamus, an area of the brain involved in appetite and energy regulation.

Ghrelin activates pathways that increase hunger, while leptin generally suppresses those pathways.

In simple terms: before you eat, hunger signals become stronger. After you eat, ghrelin usually falls and satiety signals become more prominent.

So what happens when those signals aren’t working normally?

This is where things get more complicated than simply being “hungry” or “not hungry.”

People with obesity often have higher leptin levels, not lower ones. The problem can be that the brain becomes less responsive to leptin, often referred to as leptin resistance. There may be plenty of leptin circulating, but its message isn’t having the same effect.

Ghrelin responses can also change with obesity and weight loss. And when someone loses a significant amount of weight, the body often responds by lowering leptin and increasing hunger signals, including ghrelin.

That can make maintaining weight loss harder than losing the weight initially. Your body is essentially responding to weight loss by trying to increase food intake and conserve energy.

Why this matters

Persistent hunger isn’t necessarily a sign that someone lacks discipline. Appetite is influenced by hormones, the brain, sleep, stress, food composition, medications, genetics, and many other factors.

That’s also why effective weight management often involves more than simply telling someone to “eat less.” Adequate protein and fiber, regular meals, sleep, physical activity, and stress management can all affect appetite and satiety. For some people, medications can also help modify the biological pathways involved in hunger and fullness.