Obesity

A chronic condition characterised by excess body fat that can impair health. Obesity is generally defined as a BMI of 30 kg/m² or greater.

Weight (kg) divided by height (m) squared.

Leptin

Excess energy is stored as triglycerides in adipocytes within adipose tissue.

Adipocytes enlarge (hypertrophy) and may increase in number (hyperplasia). When storage capacity is exceeded, fat may accumulate in ectopic sites.

Enlarged adipocytes release inflammatory signals and attract macrophages, causing chronic low-grade inflammation that contributes to insulin resistance and cardiovascular risk.

Changes in gut microbiome composition may influence energy extraction from food, appetite, gut barrier function and inflammation.

Type 2 diabetes; insulin resistance; dyslipidaemia; hypertension.

Impaired immune responses; increased risk of infection; increased risk of some cancers.

Metabolic dysfunction-associated steatotic liver disease (MASLD, formerly NAFLD); liver cirrhosis; hepatocellular carcinoma.

Sustained weight loss through dietary changes and increased physical activity.

Gastro-oesophageal reflux disease (GORD); gallstones; colorectal cancer.

Visceral fat accumulates around internal organs and releases free fatty acids and inflammatory cytokines into the portal circulation.

Less than 0.5.

0.5–0.59.

0.6 or above.

Waist-to-height ratio, as it gives an indication of central adiposity and accounts for fat distribution.

Lifestyle and behavioural modifications; medications such as orlistat, semaglutide, liraglutide and tirzepatide; bariatric surgery.

Medicines are considered alongside a reduced-calorie diet and increased physical activity, after lifestyle approaches have been started and evaluated. Eligibility depends on the specific medication and NICE criteria.

Offer referral for specialist assessment if BMI is ≥40, or 35–39.9 with a significant health condition that could improve with weight loss. Lower BMI thresholds may apply to some ethnic groups.