obesity
Obesity is the accumulation of excess body fat to a degree that harms health. It is best understood not as a simple failure of willpower but as a chronic disease in which the body's energy-regulating systems settle and defend a higher amount of stored fat than is healthy.
Clinically, obesity is often screened using body mass index (BMI), with a value of 30 or above commonly defining obesity in adults, though BMI is a rough tool that does not measure fat distribution or muscle. More important biologically is where fat sits: visceral fat around the abdominal organs is far more metabolically harmful than fat under the skin. Excess and dysfunctional fat tissue behaves as an active endocrine organ, releasing inflammatory signals and altered adipokines (more leptin, less adiponectin) that drive insulin resistance.
These endocrine changes link obesity to type 2 diabetes, metabolic syndrome, cardiovascular disease, certain cancers, and reproductive problems such as polycystic ovary syndrome. Importantly, the same hormonal feedback that defends energy stores actively resists weight loss, which is why obesity is chronic and relapsing, and why effective treatment increasingly relies on hormone-based drugs and, in severe cases, surgery rather than dieting alone.
A patient with central (visceral) obesity, high blood pressure, high triglycerides, and elevated fasting glucose meets the criteria for metabolic syndrome, illustrating how excess fat ripples into several endocrine problems at once.
Visceral obesity sits at the center of metabolic syndrome.
A small minority of obesity is monogenic (driven by single-gene defects, often in the leptin–melanocortin pathway), but most cases reflect many genes interacting with an environment of abundant, energy-dense food.