Obesity
Understanding obesity — assessment, causes and evidence-based management
Obesity is a complex, chronic condition defined as excess body fat that impairs health. In the UK, over 28% of adults are obese (BMI ≥30 kg/m²), making it one of the most significant public health challenges. Obesity substantially increases risk of type 2 diabetes, cardiovascular disease, certain cancers, and mental health conditions.
Assessment and classification
BMI (body mass index) is the standard screening tool: BMI ≥30 kg/m² defines obesity in most adults. For people of South Asian, Chinese, and other Asian backgrounds, the threshold is lowered to BMI ≥27.5 kg/m² due to higher cardiometabolic risk at lower BMI (NICE CG189). Waist circumference is an important adjunct: high risk at >88 cm (women) or >102 cm (men). Overweight is defined as BMI 25–29.9. Assessment should include comorbidities (T2DM, hypertension, sleep apnoea, NAFLD, osteoarthritis), mental health, medications (weight-promoting drugs), and psychological and social factors.
Lifestyle intervention
Lifestyle intervention is first-line for all patients: calorie-controlled diet (deficit of 500–600 kcal/day), increased physical activity (150 min moderate activity per week), and behaviour change techniques. Very low calorie diets (VLCD) — <800 kcal/day for 12 weeks — can achieve rapid weight loss (10–15 kg) and are recommended by NICE NG187 for type 2 diabetes remission pathways when supported by a multidisciplinary team. Referral to a structured weight management programme is recommended for those with BMI ≥30 (or ≥28 with a comorbidity). Behaviour change support and psychological input improve long-term outcomes.
Bariatric surgery
Bariatric surgery is the most effective long-term weight loss intervention. NICE CG189 criteria: BMI ≥40 kg/m², or BMI ≥35 kg/m² with a significant obesity-related comorbidity (e.g. T2DM, hypertension, obstructive sleep apnoea), after all other interventions have been tried. Expedited referral for surgery is recommended for recent-onset T2DM with BMI ≥35. Procedures include Roux-en-Y gastric bypass, sleeve gastrectomy, and adjustable gastric banding. Surgery requires lifelong nutritional supplementation, monitoring, and follow-up. Multidisciplinary assessment (including psychological evaluation) is mandatory pre-operatively.
Multidisciplinary and long-term management
Obesity is a chronic, relapsing condition requiring long-term support rather than a single intervention. NICE NG187 emphasises multidisciplinary care: dietitian, physical activity specialist, psychologist, and physician. Address contributing factors: sleep deprivation, stress, medications, and mental health. Review weight-promoting medications (e.g. insulin, antipsychotics, steroids) and consider alternatives where possible. All interventions should be delivered with sensitivity, avoiding stigmatising language. Weight stigma adversely affects engagement with healthcare. An evaluation of comorbidities should be conducted regularly — treating obesity is as important as treating its complications.