Physiology

Ghrelin and leptin: the hormones behind hunger and fullness

Two hormones help explain why dieting gets harder over time — and which habits make hunger easier to manage.

Appetite is regulated by a network of signals between the gut, fat tissue and the brain, and two hormones get most of the attention. Ghrelin, produced mainly in the stomach, rises before meals and tends to increase hunger, then falls after eating. Leptin is released by fat tissue roughly in proportion to how much fat the body carries, and it signals longer-term energy availability to the brain, helping to reduce appetite and support normal energy expenditure when stores are adequate.

These signals help explain why sustained dieting becomes harder. When people lose fat, leptin levels fall, sometimes faster than fat mass itself, and ghrelin often rises, which together push hunger up and can slightly reduce energy expenditure. This is part of the body's defense against losing energy stores and one reason why weight regain is common after aggressive diets. People with obesity often have high leptin levels but respond less to them, a state described as leptin resistance, so simply having more leptin does not guarantee lower appetite.

You cannot switch these hormones off, but several habits make hunger easier to manage. Prioritizing protein and fiber-rich foods increases fullness, eating enough vegetables and whole foods adds volume for fewer calories, and regular meal patterns help some people anticipate hunger rather than be overwhelmed by it. Sleep matters as well: short sleep tends to raise ghrelin and lower leptin, increasing appetite the next day. A moderate energy deficit, occasional maintenance phases and strength training to preserve muscle make long-term fat loss more sustainable than very aggressive cuts.

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