Key Facts

Obesity is one of the greatest public health challenges facing the UK. It is a chronic, relapsing condition with complex genetic, environmental, and behavioural contributions. Effective management requires a multicomponent approach.

Epidemiology

• Prevalence: 28% of UK adults are obese; 64% are overweight or obese
• Obesity prevalence is highest in the most deprived areas (36% vs 20% in least deprived)
• Childhood obesity: 23% of Year 6 children in England
• NHS costs attributable to overweight and obesity: estimated £6.5 billion/year

Aetiology

• Energy imbalance: chronic caloric surplus relative to expenditure
• Genetic factors: polygenic contribution (FTO, MC4R genes); monogenic obesity rare (leptin deficiency, MC4R mutations)
• Environmental: obesogenic environment (processed food availability, sedentary lifestyles, portion sizes)
• Psychological: emotional eating, binge eating disorder, depression
• Medical: hypothyroidism, Cushing syndrome, PCOS, medications (corticosteroids, antipsychotics, insulin, beta-blockers, sodium valproate)
• Gut microbiome: emerging evidence for role in energy harvest and metabolism

Health Consequences

• Type 2 diabetes: risk 5-10× higher in obese individuals
• Cardiovascular disease: hypertension, coronary artery disease, heart failure, stroke
• Cancer: 13 cancers linked to obesity (endometrial, breast post-menopause, colorectal, oesophageal, kidney, pancreatic, liver)
• Musculoskeletal: osteoarthritis, back pain
• Respiratory: obstructive sleep apnoea, obesity hypoventilation syndrome
• Metabolic: NAFLD/NASH, dyslipidaemia, metabolic syndrome
• Mental health: depression, anxiety, reduced quality of life

Assessment

• BMI: primary screening tool (weight in kg / height in m²)
• Waist circumference: additional CVD risk if ≥94cm (men) or ≥80cm (women); substantially increased if ≥102cm (men) or ≥88cm (women)
• Consider ethnicity-adjusted thresholds: South Asian BMI ≥23 (overweight), ≥27.5 (obese)

Assessment of Comorbidities

• Blood pressure
• HbA1c/fasting glucose
• Lipid profile
• Liver function (NAFLD)
• Thyroid function
• Sleep history (OSA)
• Mental health assessment
• Joint symptoms

Red Flags

• Rapid unexplained weight gain — exclude Cushing syndrome, hypothyroidism, medication effect
• BMI ≥50 — very high surgical and anaesthetic risk; urgent specialist input
• Signs of secondary obesity (striae, proximal weakness, moon face) — investigate endocrine cause
• Binge eating disorder — psychological/psychiatric assessment
• Severe OSA (daytime somnolence, Epworth >10) — sleep clinic referral

Bedside

• Height, weight, BMI calculation
• Waist circumference
• Blood pressure

Bloods

• HbA1c or fasting glucose (diabetes screening)
• Lipid profile
• LFTs (NAFLD screening)
• TFTs (exclude hypothyroidism)
• U&Es

Imaging

• Liver USS or FibroScan: if NAFLD/NASH suspected
• DEXA: rarely needed; for body composition analysis in research

Special Tests

• Epworth Sleepiness Scale and sleep study: if OSA suspected
• Overnight dexamethasone suppression test: if Cushing syndrome suspected
• Psychological assessment: if eating disorder suspected

Non-pharmacological (NICE CG189)

Tier 1 — Universal prevention:

• Public health messaging, food labelling, sugar tax

Tier 2 — Lifestyle intervention (first-line for all):

• Dietary modification: 600 kcal/day deficit; balanced diet; avoid very low-calorie diets unless supervised
• Physical activity: ≥150 minutes moderate-intensity aerobic activity/week; aim for 300 min/week for weight loss maintenance
• Behavioural support: goal setting, self-monitoring (food diary, regular weighing), stimulus control, cognitive restructuring
• NHS weight management programmes (e.g. NHS Digital Weight Management Programme)
• Total diet replacement programmes (800 kcal/day for 12 weeks) for BMI ≥30 with diabetes (NICE guideline)

Tier 3 — Specialist weight management:

• Multidisciplinary team: dietitian, psychologist, physician, exercise specialist
• Psychological therapy for eating disorders
• Pharmacotherapy initiation and monitoring

Pharmacological

Orlistat (Xenical) 120mg TDS:

• Pancreatic lipase inhibitor; reduces fat absorption by 30%
• Additional weight loss: 3-4kg over 12 months vs placebo
• Side effects: oily stools, faecal urgency, fat-soluble vitamin deficiency
• Continue only if ≥5% weight loss at 3 months
• Available OTC (Alli 60mg) for BMI ≥28

Semaglutide 2.4mg SC weekly (Wegovy):

• GLP-1 receptor agonist; reduces appetite and caloric intake
• STEP trials: 15-17% weight loss at 68 weeks
• NICE TA875: for BMI ≥35 (or ≥30 with weight-related comorbidity) as part of specialist weight management
• SELECT trial: 20% reduction in MACE (cardiovascular benefit independent of diabetes status)
• Dose escalation over 16 weeks to target dose
• Side effects: nausea (most common), vomiting, diarrhoea, constipation

Liraglutide 3.0mg SC daily (Saxenda):

• GLP-1 receptor agonist; weight loss approximately 8% at 56 weeks
• NICE TA664 (more limited criteria than semaglutide)

Tier 4 — Bariatric surgery (NICE CG189):

• Consider if: BMI ≥40, or BMI ≥35 with significant comorbidity, or BMI 30-34.9 with recent-onset T2DM
• Procedures:
  • Roux-en-Y gastric bypass: gold standard; 25-35% total body weight loss
  • Sleeve gastrectomy: 20-25% weight loss; now most commonly performed
  • Adjustable gastric band: less effective; declining use
• Type 2 diabetes remission: 60-80% after Roux-en-Y
• Requires lifelong follow-up, nutritional supplementation, psychological support

Referral Criteria

• Tier 3 weight management: BMI ≥40, or BMI ≥35 with comorbidity failing Tier 2
• Bariatric surgery assessment: as per NICE CG189 criteria
• Suspected secondary obesity (endocrine): endocrinology
• Eating disorder: psychiatric/psychology referral

• 5-10% weight loss: reduces T2DM risk by 58% (DPP trial), improves BP by 5-10 mmHg, reduces LDL cholesterol
• Lifestyle interventions: average weight loss 3-5% at 12 months; weight regain common
• Semaglutide 2.4mg: 15-17% weight loss at 68 weeks; weight regain occurs on discontinuation
• Bariatric surgery: most effective long-term intervention; sustained 20-35% weight loss at 10+ years; reduces all-cause mortality by 40%
• Weight cycling ('yo-yo dieting'): associated with adverse metabolic and psychological outcomes
• Childhood obesity: 80% of obese adolescents become obese adults

BMI Classification

Bariatric Surgery Eligibility (NICE CG189)