Obesity

Definition

Obesity is a chronic, multifactorial disease characterized by excessive fat accumulation that may impair health. It is usually defined by body mass index (BMI) ≥30 kg/m² in adults, with severity classified as class I–III.

Epidemiology

• Affects over 650 million adults globally
• Prevalence has risen steadily over past decades
• More common in high-income countries, but rising in low- and middle-income countries
• Associated with age, sex, genetics, and lifestyle factors

Etiology

• Energy imbalance: caloric intake exceeds expenditure
• Genetic factors: monogenic obesity (e.g., leptin deficiency), polygenic obesity
• Endocrine disorders: hypothyroidism, Cushing’s syndrome, polycystic ovary syndrome (PCOS)
• Medications: corticosteroids, antipsychotics, insulin, sulfonylureas
• Environmental: sedentary lifestyle, high-calorie diets, urbanization
• Psychosocial factors: stress, depression, sleep deprivation

Pathophysiology

• Chronic positive energy balance → adipocyte hypertrophy and hyperplasia
• Dysregulation of leptin and ghrelin → impaired appetite control
• Insulin resistance and low-grade inflammation in adipose tissue
• Altered lipid metabolism and ectopic fat deposition
• Neuroendocrine and gut-brain signaling disturbances perpetuate obesity