What is Obesity?
Quick read · 4 min
Obesity is a chronic medical condition involving excess body fat — driven by biology, not personal failure. Major medical organisations now classify it as a disease requiring long-term management.
Obesity is now classified as a chronic disease by major medical organizations — driven by biology, not personal failure.
How obesity is defined
In clinical settings, obesity is most commonly defined using Body Mass Index (BMI) — a ratio of weight to height. It correlates broadly with health risk at the population level.
BMI classifications
World Health Organization standard categories
BMI is a screening tool, not a perfect individual measure. See limitations below.
Limitations of BMI
Muscle vs fat
BMI does not distinguish between fat mass and lean muscle mass — a heavily muscular person may have a high BMI without excess body fat.
Fat distribution
Visceral fat (around the abdomen) carries higher metabolic risk than subcutaneous fat, but BMI cannot tell them apart.
Ethnic variation
Asian populations may have metabolic risk at lower BMI thresholds. Some clinical guidelines apply lower cut-offs for this group.
Better alternatives exist
Waist circumference and waist-to-height ratio are increasingly used alongside BMI to better capture cardiometabolic risk.
Obesity as a chronic disease
Major medical organisations — including the World Health Organization, American Medical Association, and European Association for the Study of Obesity — now classify obesity as a chronic, relapsing disease.
This classification reflects the biological reality: obesity involves dysregulation of hormonal signals that control appetite and energy storage, which means it cannot be permanently resolved by willpower alone. The same is true of other chronic diseases like hypertension or type 2 diabetes — they are managed, not cured.
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Last reviewed: April 2026