Leptin
A hormone made by fat tissue that tells the brain how much energy is stored and helps control appetite. Its level rises with body fat; in obesity it is usually high because the body becomes resistant to its 'I'm full' signal. Rare low levels cause severe childhood obesity.
What it measures
Leptin is a hormone produced mainly by fat (adipose) tissue. It acts as a signal to the brain about the body's energy stores: when fat stores are ample, leptin rises and tells the brain to reduce appetite and increase energy use, and when fat stores fall (as in fasting or weight loss), leptin drops and drives hunger. Because leptin tracks fat mass, its blood level is generally higher in people with more body fat. The paradox of common obesity is 'leptin resistance': despite high leptin levels, the brain no longer responds properly to the fullness signal, so appetite is not suppressed. Measuring leptin is not part of routine care — most people with obesity have high leptin, which does not change management. Its specific clinical value is in rare situations: a very low or absent leptin level, from an inherited leptin deficiency, causes severe obesity from early childhood and is one of the few forms of obesity treatable with leptin replacement. Leptin is also studied in research on metabolism, appetite regulation and conditions with very low body fat (lipodystrophy).
What a high value can mean
- Higher body fat with leptin resistance — the usual pattern in common obesity; high leptin that the brain no longer responds to.
- Part of the metabolic picture — often accompanies insulin resistance and related markers.
- Not usually a target of treatment in itself — in common obesity, a high level reflects fat mass rather than a treatable deficiency.
What a low value can mean
- Low body fat — expected in very lean individuals, athletes, or after significant weight loss or fasting.
- Congenital leptin deficiency (rare) — very low or absent leptin causing severe early-childhood obesity; treatable with leptin replacement.
- Lipodystrophy — conditions with very little fat tissue.
When to discuss with a doctor
Leptin is a specialised, mostly research-oriented test rather than a routine one, and a high level in common obesity does not by itself change management — it simply reflects fat mass and the leptin resistance that characterises obesity. Its important, if uncommon, use is in suspected inherited leptin deficiency: a child with severe, early obesity and very low leptin may have a treatable cause, assessed by specialists. It is also used in evaluating lipodystrophy and in metabolic research. For most people, weight and metabolic health are managed through the familiar levers of diet, activity, sleep and related conditions rather than a leptin measurement. Mediora.AI shows leptin alongside insulin and metabolic markers where it appears so it is read in context; its interpretation belongs with your doctor.