Obesity

Obesity is a chronic, relapsing disease of excess or dysfunctional adipose tissue that impairs health. In adults it is defined by a body mass index (BMI) of 30 kg/m2 or more (27.5 kg/m2 or more in Asian populations), or by waist circumference or waist to height ratio of 0.5 or more indicating central adiposity.

• Classes: class I BMI 30 to 34.9; class II 35 to 39.9; class III 40 or more (in South Asian, Chinese, Japanese and Middle Eastern populations the class thresholds are 2.5 kg/m2 lower).
• Causes: energy intake exceeding expenditure with genetic, environmental, psychological and social contributors; medicines (antipsychotics such as olanzapine, mirtazapine, amitriptyline, valproate, insulin, sulfonylureas, corticosteroids, beta blockers, and oral contraceptive depot injections); endocrine causes (hypothyroidism, Cushing syndrome, polycystic ovary syndrome, hypothalamic disease, growth hormone deficiency, hypogonadism); monogenic forms (leptin, melanocortin 4 receptor) in severe early onset obesity; sleep deprivation; binge eating disorder.
• Complications: type 2 diabetes, hypertension, dyslipidaemia, coronary disease, heart failure, stroke, atrial fibrillation, venous thromboembolism, sleep apnoea, fatty liver disease, osteoarthritis, gout, reflux, gallstones, infertility, pregnancy complications, urinary incontinence, depression, and cancers (breast after menopause, colon, endometrial, kidney, oesophageal adenocarcinoma, liver, pancreatic).
• Weight loss of 5 to 10 percent improves glucose, blood pressure and lipids; 15 percent or more can put type 2 diabetes into remission.

• Increased weight and waist circumference; breathlessness, joint pain, snoring and daytime sleepiness, heartburn, fatigue, low mood, skin intertrigo, acanthosis nigricans, stress incontinence, menstrual irregularity.
• Clues for secondary causes: rapid gain, purple striae, moon face, proximal weakness, hypertension (Cushing); cold intolerance and constipation (hypothyroidism); hirsutism and irregular cycles (polycystic ovary syndrome); early onset severe obesity with hyperphagia (genetic); headache and visual loss (hypothalamic or pituitary disease).
• Weight history, dietary pattern, activity, sleep, medicines, eating behaviours, mental health, and previous weight loss attempts (use a non-judgemental approach and ask permission to discuss weight).

• Measure height, weight, BMI and waist circumference (midpoint between rib margin and iliac crest; high risk above 94 cm men and 80 cm women, very high risk above 102 cm and 88 cm). Check blood pressure and heart rate.
• Investigations: HbA1c or fasting glucose, lipid profile, liver tests, creatinine and eGFR, thyroid stimulating hormone; urine albumin to creatinine ratio; pregnancy test when relevant.
• Screening for sleep apnoea (STOP-BANG questionnaire; polysomnography if positive), fatty liver (FIB-4 score), depression, binge eating.
• Additional tests when suspected: overnight dexamethasone suppression test or late night salivary cortisol (Cushing), total testosterone and pelvic ultrasound (polycystic ovary syndrome), genetic testing for severe early onset.
• Children: BMI above the 95th percentile for age and sex (or BMI-for-age z score above 2); check blood pressure, lipids, glucose, ALT.
• Differentials for apparent weight gain: oedema, ascites, tumours, pregnancy, hypothyroidism.

Principles

• Obesity is a chronic disease and treatment is long term. Set realistic goals (5 to 10 percent initially, up to 15 to 20 percent with drugs or surgery). Treat complications at the same time.

Lifestyle

• Energy deficit of 500 to 750 kcal per day (1200 to 1500 kcal for women and 1500 to 1800 kcal for men), using a Mediterranean, low carbohydrate or low fat diet that the patient can sustain; protein 1.0 to 1.2 g/kg daily to preserve muscle; avoid sugary drinks and ultra processed food; structured meal replacement or total diet replacement (800 to 1000 kcal per day for 8 to 12 weeks, then food reintroduction) for BMI 30 or more with type 2 diabetes or prediabetes under supervision.
• Activity: build up to 150 to 300 minutes of moderate exercise weekly with resistance exercise twice weekly; 7,000 to 10,000 steps per day; reduce sitting; 250 minutes or more per week helps maintain weight loss.
• Sleep 7 to 8 hours; stress management; behavioural therapy (self-monitoring, goal setting, problem solving, relapse prevention); group programmes of at least 12 sessions in 6 months.

Drug treatment (BMI 30 or more, or 27 or more with weight related disease, together with lifestyle)

• Semaglutide 2.4 mg subcutaneously once weekly: 0.25 mg for 4 weeks, 0.5 mg for 4 weeks, 1 mg for 4 weeks, 1.7 mg for 4 weeks, then 2.4 mg. Mean weight loss about 15 percent.
• Tirzepatide subcutaneously once weekly: 2.5 mg for 4 weeks then increase by 2.5 mg every 4 weeks to 5, 10 or 15 mg (maintenance); mean loss about 20 percent. It lowers the efficacy of oral contraceptives, so use a barrier method for 4 weeks after starting and after each dose increase.
• Liraglutide 3 mg subcutaneously daily: 0.6 mg for a week, then increase by 0.6 mg weekly to 3 mg.
• Orlistat 120 mg orally three times daily with fat containing meals; fat soluble vitamin supplements; side effects are oily stool, urgency and flatulence.
• Naltrexone with bupropion modified release 8 mg/90 mg: 1 tablet daily in week 1, 1 tablet twice daily in week 2, 2 tablets in the morning and 1 in the evening in week 3, then 2 tablets twice daily from week 4 (avoid in uncontrolled hypertension, seizures, eating disorders, opioid use).
• Side effects of GLP-1 based medicines: nausea, vomiting, diarrhoea, constipation, reflux, gallstones, pancreatitis, dehydration with kidney injury, hypoglycaemia with insulin or sulfonylureas (reduce these doses). Contraindicated with a history of medullary thyroid carcinoma, multiple endocrine neoplasia type 2, pregnancy and breastfeeding; stop 2 months before planned pregnancy; tell the anaesthetist before elective procedures, because delayed gastric emptying raises the aspiration risk. Review at 12 to 16 weeks and stop if weight loss is under 5 percent.
• Setmelanotide is for specific monogenic obesity (specialist).

Surgery

• Bariatric surgery (sleeve gastrectomy, Roux-en-Y gastric bypass) for BMI 40 or more, 35 or more with comorbidity, and 30 or more with recent onset type 2 diabetes (lower thresholds in Asian populations). Lifelong vitamin and mineral supplementation: multivitamin, calcium 1200 to 1500 mg, vitamin D 3000 IU, iron, vitamin B12 1000 micrograms intramuscularly every 3 months, and annual blood monitoring.
• Endoscopic balloons and sleeve procedures are specialist options.

Special groups

• Pregnancy: avoid weight loss drugs; advise gestational weight gain of 5 to 9 kg for obesity; folic acid 5 mg daily before conception and until 12 weeks; aspirin 75 to 150 mg daily from 12 weeks for pre-eclampsia risk.
• Children and adolescents: family based multicomponent lifestyle programmes; semaglutide 2.4 mg or liraglutide 3 mg may be used from 12 years under specialist supervision.
• Older adults: aim for modest loss with resistance exercise and adequate protein.
• Antipsychotic users: metformin 500 mg increased to 1 g twice daily limits weight gain.

Follow up

• Review monthly during active weight loss for the first 3 to 6 months, then every 3 months; track weight, waist, blood pressure, glucose, and medicine doses (reduce antihypertensive and diabetes drugs as weight falls); plan weight maintenance, and discuss relapse as a feature of the disease.