Key Facts

Childhood obesity is one of the most significant public health challenges in the UK. It is associated with numerous physical and psychological comorbidities and tracks strongly into adult obesity, increasing lifetime cardiovascular and metabolic risk.

Epidemiology

The UK National Child Measurement Programme (NCMP) reports that approximately 10% of Reception-age children and 23% of Year 6 children in England are obese. Prevalence is higher in children from deprived areas (approximately double the rate in the most vs least deprived quintiles), certain ethnic groups (Black and South Asian), and those with disabilities. The UK has one of the highest rates of childhood obesity in Western Europe.

Aetiology

Primary/exogenous obesity (>95% of cases): Caloric intake exceeding energy expenditure.

• Excess energy-dense food, sugar-sweetened beverages
• Sedentary behaviour, excessive screen time
• Reduced physical activity
• Familial/behavioural patterns, food environment

Secondary/endogenous causes (<5%):

• Endocrine: Hypothyroidism, Cushing syndrome, GH deficiency
• Genetic: Prader-Willi syndrome, Bardet-Biedl syndrome, MC4R mutations, leptin deficiency
• Iatrogenic: Corticosteroids, antipsychotics (olanzapine, risperidone), antiepileptics (sodium valproate)

Pathophysiology

Chronic positive energy balance leads to adipocyte hypertrophy and hyperplasia. Excess adiposity, particularly visceral fat, causes low-grade chronic inflammation and insulin resistance. This drives the metabolic syndrome: hyperinsulinaemia, dyslipidaemia, hypertension, and hepatic steatosis. In children, excess weight also affects linear growth (often taller than peers before puberty) and bone/joint development.

Assessment Findings

• BMI ≥91st centile (overweight) or ≥98th centile (obese) on UK90 growth charts
• Typically tall for age (short stature suggests endocrine or genetic cause)
• Acanthosis nigricans (velvety hyperpigmented skin at neck/axillae — insulin resistance)
• Striae, particularly in adolescents

Comorbidities

• Metabolic: Insulin resistance, type 2 diabetes, dyslipidaemia, non-alcoholic fatty liver disease
• Cardiovascular: Hypertension, left ventricular hypertrophy
• Respiratory: Obstructive sleep apnoea, asthma exacerbation
• Musculoskeletal: Slipped upper femoral epiphysis (SUFE), Blount disease, flat feet
• Psychological: Bullying, low self-esteem, depression, disordered eating
• Dermatological: Intertrigo, acanthosis nigricans

Red Flags

• Short stature + obesity → suspect endocrine cause (hypothyroidism, Cushing, GH deficiency)
• Developmental delay + hypotonia + obesity in infant → consider Prader-Willi syndrome
• Severe obesity with onset <5 years → genetic/monogenic obesity screen
• Rapid unexplained weight gain → exclude Cushing syndrome, hypothyroidism

Bedside

• BMI: Calculated and plotted on UK90 growth chart (age and sex-specific centiles)
• Waist circumference: Marker of central/visceral adiposity
• Blood pressure: Screen for hypertension (use age-appropriate centile charts)
• Pubertal staging: Tanner staging

Bloods

• Fasting glucose and insulin (or HbA1c): Screen for insulin resistance/T2DM — HbA1c ≥48 mmol/mol = diabetes
• Fasting lipid profile: Total cholesterol, LDL, HDL, triglycerides
• LFTs (ALT): Screen for non-alcoholic fatty liver disease
• TFTs: Exclude hypothyroidism (if short stature or clinical suspicion)
• 8am cortisol or overnight dexamethasone suppression test: If Cushing suspected

Imaging

• Liver ultrasound: If elevated ALT — assess for hepatic steatosis
• Bone age (wrist X-ray): If growth concern — advanced in exogenous obesity, delayed in endocrine causes
• Sleep study (polysomnography): If obstructive sleep apnoea suspected

Special Tests

• Genetic testing: Prader-Willi methylation, MC4R sequencing — if early onset, severe, or syndromic features
• Oral glucose tolerance test: If high-risk for T2DM (family history, acanthosis nigricans, ethnic background)

Non-pharmacological

• Lifestyle modification (first-line, NICE CG189): Family-based behavioural programme including diet, physical activity, and behavioural change
• Dietary: Reduce energy-dense foods, increase fruit/vegetables, reduce sugar-sweetened drinks; avoid restrictive dieting in children
• Physical activity: ≥60 minutes moderate-vigorous activity daily; reduce sedentary screen time to <2 hours/day
• Behavioural: Motivational interviewing, SMART goal-setting, whole-family approach, regular monitoring
• School-based interventions: Healthy eating policies, physical activity programmes

Pharmacological

• Orlistat 120mg TDS with meals: Only option licensed for ≥12 years in the UK; inhibits gastric and pancreatic lipase reducing fat absorption by ~30%; side effects include steatorrhoea, fat-soluble vitamin deficiency
• Metformin: Sometimes used off-licence for insulin resistance or impaired glucose tolerance in adolescents
• GLP-1 receptor agonists (e.g., liraglutide): Emerging evidence for adolescent obesity; licensed in some settings

Surgical/Interventional

• Bariatric surgery: NICE CG189 states may be considered in exceptional circumstances for adolescents who have achieved or nearly achieved physiological maturity, BMI ≥40 (or ≥35 with significant comorbidity), and have failed all other interventions
• Options: Sleeve gastrectomy (most common in adolescents), Roux-en-Y gastric bypass

Referral Criteria

• BMI ≥98th centile — consider referral to paediatric weight management programme
• Suspected secondary cause — paediatric endocrinology
• Significant comorbidities (T2DM, OSA, NAFLD, SUFE) — appropriate specialist
• Extreme obesity (BMI ≥3.5 SD above mean) — specialist obesity services

• Tracking into adulthood: ~80% of obese adolescents become obese adults
• Metabolic risk: Obese children have 4× higher risk of developing T2DM in adulthood
• Cardiovascular: Childhood obesity associated with increased adult cardiovascular mortality (HR ~1.5-2)
• Lifestyle interventions: Modest effect — average BMI reduction of 0.5-1 BMI z-score unit with intensive programmes
• Bariatric surgery: Effective in selected adolescents — 25-35% total weight loss maintained at 5 years
• Psychological: Childhood obesity associated with reduced quality of life and increased risk of adult depression

UK Classification of Childhood Weight Status

Screening Recommendations for Obese Children