Child Obesity — Causes, Health Risks & Treatment Guide for Parents — Symptoms, Causes & Treatment | MyMedicPlus

Childhood obesity is defined as excess body fat to an extent that adversely affects health. In children, overweight and obesity are defined by age- and sex-specific BMI percentile thresholds (rather than absolute BMI cut-offs used in adults). In the UK, over the 91st centile is overweight; over the 98th centile is obese. Globally, 39 million children under 5 and 340 million children aged 5-19 are overweight or obese — a tripling since 1975. Childhood obesity is associated with significant immediate and long-term health consequences including metabolic syndrome, Type 2 diabetes, cardiovascular disease, obstructive sleep apnoea, non-alcoholic fatty liver disease, and psychological morbidity. The rapid global rise in childhood obesity represents a public health crisis driven by obesogenic environments — characterised by abundant cheap ultra-processed food, markedly reduced opportunities for physical activity, and extensive screen time — requiring systemic and societal responses that go far beyond individual behaviour change interventions.

Childhood obesity results from a complex interaction of genetic, environmental, and behavioural factors. Energy imbalance — consuming more calories than are expended — drives weight gain. Key contributors: excess consumption of ultra-processed foods, sugary drinks (fruit juices, fizzy drinks), and large portion sizes; insufficient physical activity and excessive screen time (television, gaming, social media); family dietary habits and parental obesity (genetics + shared environment); socioeconomic deprivation (low-income families have higher obesity rates due to food environment, stress, and activity limitations); poor sleep (sleep deprivation increases ghrelin/leptin imbalance, increasing appetite); secondary causes (rarer): hypothyroidism, Cushing's syndrome, Prader-Willi syndrome, craniopharyngioma; early introduction of solid foods and formula feeding.

BMI above the 91st centile for age and sex on the UK growth chart indicates overweight; above the 98th centile indicates obesity. Children with obesity may have: acanthosis nigricans (dark velvety skin patches in axilla and neck folds — sign of insulin resistance); striae (stretch marks on abdomen, hips, thighs); hepatomegaly (from NAFLD — non-alcoholic fatty liver disease); snoring and daytime somnolence (obstructive sleep apnoea); Blount's disease (bowing of the legs — from excess weight on growing bones); slipped capital femoral epiphysis (hip/knee pain — orthopaedic complication); hypertension; and psychological signs (low self-esteem, poor body image, anxiety, depression, social isolation, bullying).

Assessment: accurate measurement of height and weight; BMI calculated (weight in kg divided by height in metres squared); plotted on age- and sex-specific centile charts (UK-WHO growth charts). Waist circumference-to-height ratio is a useful additional measure of central adiposity (ratio above 0.5 indicates excess abdominal fat). Investigations for metabolic complications: fasting glucose and HbA1c (Type 2 diabetes/pre-diabetes); fasting lipid profile (dyslipidaemia — elevated triglycerides, low HDL); liver function tests and liver ultrasound (NAFLD); blood pressure; and thyroid function (to exclude hypothyroidism). Sleep study (polysomnography) if obstructive sleep apnoea suspected. Genetic testing or specialist referral if secondary cause suspected (rapid weight gain before age 2, extreme obesity, or dysmorphic features).

Family-based multicomponent lifestyle intervention is the cornerstone of treatment and is most effective when the whole family participates. Components: dietary change — reduce ultra-processed foods and sugary drinks; increase fruit, vegetables, whole grains, and lean protein; structured meals and snacks without screens; reduce portion sizes; physical activity — 60 minutes of moderate-to-vigorous physical activity daily; limit recreational screen time (under 2 hours/day); increase incidental activity (active travel, less time sitting). Behaviour change: cognitive behavioural therapy (CBT) techniques, motivational interviewing, goal-setting, and family support programmes. Pharmacological treatment for severe adolescent obesity (BMI above 35 with comorbidities, or over 99.6th centile): GLP-1 receptor agonists (semaglutide — Wegovy — approved in the USA and UK for adolescents aged 12+ with BMI 95th centile or above); liraglutide (Saxenda) also approved for adolescents in some countries. Bariatric surgery (sleeve gastrectomy or Roux-en-Y gastric bypass) for severe adolescent obesity — highly effective but considered only after optimal medical management and psychological assessment.

Childhood obesity tracks strongly into adulthood — 60-80% of obese children remain obese as adults. Metabolic complications in obese children include: Type 2 diabetes (now affecting children in the UK, USA, and globally — previously almost exclusively an adult condition); non-alcoholic fatty liver disease (NAFLD) — occurring in 30-40% of obese children, can progress to cirrhosis; dyslipidaemia (elevated triglycerides, reduced HDL cholesterol); hypertension; obstructive sleep apnoea (reduced school performance, cardiovascular effects); and polycystic ovarian syndrome (PCOS) in adolescent girls. Psychological complications are profound: bullying, depression, anxiety, low self-esteem, and disordered eating. Orthopaedic complications: Blount's disease, slipped capital femoral epiphysis, flat feet, knee pain.

Breastfeed exclusively for 6 months where possible — breastfed infants have 15-25% lower obesity risk. Introduce solid foods at 4-6 months, not earlier. Model healthy eating habits — children learn from what parents eat. Limit sugary drinks (fruit juice, squash, fizzy drinks) and ultra-processed foods. Maintain regular family mealtimes without screens (television, phones). Encourage at least 60 minutes of physical activity every day — walk or cycle to school, participate in sports, play outside. Limit recreational screen time to 1 hour per day for children aged 2-5 and 2 hours for older children (WHO recommendation). Prioritise 9-11 hours of sleep per night (children aged 6-12). NHS weight management programmes and community referrals are available for children above the 91st centile with complications, or above the 98th centile.

See your child's GP or paediatrician for: a child with BMI above the 95th percentile for age and sex (clinical obesity); obesity present in a child under 5 years; obesity associated with complications such as sleep apnoea (snoring, gasping, excessive daytime tiredness), joint pain, or fatigue significantly limiting activity; signs of depression, bullying, or significant self-esteem issues related to weight; suspected emotional or disordered eating patterns; or obesity in a child where a medical cause is suspected (growth faltering — short stature — combined with obesity may indicate endocrine cause such as hypothyroidism or Cushing's). Seek urgent assessment for: a markedly overweight child with severe breathlessness (possible obesity hypoventilation syndrome or severe sleep apnoea); or signs of type 2 diabetes (excessive thirst, frequent urination, fatigue, blurred vision). All children above the 91st BMI percentile qualify for specialist tier 2 or tier 3 weight management services in the UK — referral from GP is the pathway.