Obesity

Overview

•BMI = weight (kg) / height (m²) - standard screening tool; does not account for fat distribution

Classification	Standard BMI (kg/m²)	South Asian / Black African / African-Caribbean BMI (kg/m²)
Overweight	25-29.9	≥23
Obesity	≥30	≥27.5

•Waist-to-height ratio (WtHR) - use alongside BMI when BMI <35 kg/m² to assess central adiposity

•Healthy: 0.4-0.49 | Increased risk: 0.5-0.59 | High risk: ≥0.6

⚠️

Ethnic minority populations accumulate visceral fat at lower total body weight - use lower BMI thresholds (≥23 overweight, ≥27.5 obesity) for South Asian, Chinese, Black African, and African-Caribbean patients. Apply these same lower cut-offs when considering pharmacotherapy or surgery.

Investigations

🥇 First-line

•BMI + waist circumference/WtHR, blood pressure, fasting glucose + HbA1c, fasting lipid profile, LFTs (screen for MASLD), TSH (exclude hypothyroidism)

•Second-line (if Cushing's suspected): 24-hour urinary cortisol or overnight dexamethasone suppression test

Management

•Seek permission before discussing weight; use compassionate, non-judgmental approach

🥇 First-line

•multicomponent lifestyle intervention - calorie-controlled diet + physical activity + structured behavioural programme

•Pharmacotherapy - consider if lifestyle measures insufficient after 3-6 months:

•Orlistat (pancreatic lipase inhibitor) - BMI ≥30 (or ≥27.5 in high-risk ethnic groups) with comorbidities

•GLP-1 receptor agonists (e.g. liraglutide, semaglutide) - as per NICE criteria

•Bariatric surgery - most durable long-term weight loss; associated with remission of type 2 diabetes; apply ethnicity-adjusted BMI thresholds for referral

💡

Even modest weight loss of 5-10% of body weight produces clinically significant improvements in blood pressure, glucose tolerance, lipid profile, and OSA severity - patients do not need to reach a 'normal BMI' to benefit.

Complications

•Cardiovascular - hypertension, ischaemic heart disease, stroke (driven by visceral fat → insulin resistance, dyslipidaemia, systemic inflammation)

•Metabolic - type 2 diabetes, dyslipidaemia (raised triglycerides, low HDL), metabolic syndrome

•Respiratory - obstructive sleep apnoea (snoring, witnessed apnoeas, daytime somnolence), breathlessness

•Musculoskeletal - osteoarthritis of knees, hips, lumbar spine

•Hepatic - MASLD (metabolic dysfunction-associated steatotic liver disease / NAFLD)

•Psychological - depression, low self-esteem, social isolation

Prognosis

•Severe obesity (Class III) reduces life expectancy by approximately 8-10 years

•Obesity is a chronic relapsing condition - weight regain after intervention is common; long-term support is essential

Secondary Causes

•Medical: hypothyroidism, Cushing's syndrome, PCOS, hypothalamic damage, growth hormone deficiency

•Genetic: Prader-Willi syndrome, Laurence-Moon-Biedl syndrome

•Weight-gaining medications: corticosteroids, antipsychotics (clozapine, quetiapine, haloperidol, lithium), antidepressants (amitriptyline, MAOIs), anticonvulsants (valproate, gabapentin, pregabalin, carbamazepine), glucose-lowering agents (insulin, sulfonylureas, thiazolidinediones), beta-blockers