Paediatrics chapters
Childhood obesity
How overweight and obesity are defined in children using BMI-for-age, how to tell simple obesity from endocrine and genetic causes, the complications to screen for, and how to manage and prevent it.
- In children, obesity is judged by BMI-for-age: 85th to under 95th centile = overweight, 95th centile or above = obese (WHO Z-scores: above +1 SD overweight, above +2 SD obese from 5 years).
- Most obese children have simple (exogenous) obesity: they are tall for age with normal development; an obese child who is short or growing slowly suggests an endocrine cause, and dysmorphism or delay suggests a syndrome such as Prader-Willi.
- Screen for hypertension, type 2 diabetes, dyslipidaemia, fatty liver, sleep apnoea and slipped capital femoral epiphysis; treat with family-based diet, activity and behaviour change.
On this page
Overview
Obesity is now among the commonest forms of malnutrition, rising quickly in urban Pakistan alongside undernutrition (the "double burden"). Obese children often become obese adults, and the risk of persisting obesity rises with age and severity. Childhood obesity brings early hypertension, type 2 diabetes, fatty liver and psychological harm.
Definition and BMI
BMI = weight (kg) ÷ height (m)²
In adults fixed cut-offs (25 and 30) are used. In children BMI changes normally with age and sex, so it must be plotted on a BMI-for-age chart.
| BMI-for-age (CDC centiles) | Category |
|---|---|
| Below the 5th centile | Underweight |
| 5th to under the 85th | Healthy weight |
| 85th to under the 95th | Overweight |
| 95th or above | Obese |
WHO BMI-for-age Z-scores (5-19 years): thinness below −2 SD, overweight above +1 SD, obesity above +2 SD.
12-year-old boy, weight 67 kg, height 151 cm (1.51 m)
BMI = 67 ÷ (1.51 × 1.51) = 67 ÷ 2.28 = 29.4 kg/m²
Plotted for age: above the 95th centile → obese (an adult cut-off would mislead in a child)
Role of BMI: simple, cheap screening; tracks change over time; correlates with body fat and later risk. Limits: it does not separate fat from muscle and does not show fat distribution, so add waist circumference and examination.
Do not apply adult BMI cut-offs (25 and 30) to children. A BMI of 22 may be normal at 16 years but obese at 6 years.
Classification
| Basis | Types |
|---|---|
| Cause | Simple (exogenous, nutritional), the large majority; endogenous: endocrine, genetic or syndromic, hypothalamic, drug-induced |
| Fat distribution | Central (android, abdominal): higher cardiometabolic risk; generalised (gynoid) |
| Severity | Overweight, obese, severely obese (well above the 99th centile) |
Causes and risk factors
Simple obesity (energy intake above energy use):
- Family pattern: obese parents; children of obese mothers are 3-5 times more likely to be obese (Akbar).
- Diet: fast food, sugary drinks and juices, large portions, snacking, food used as a reward.
- Inactivity: television, mobile and video games, little outdoor play, car travel.
- Formula feeding with overfeeding in infancy; rapid catch-up weight gain in small-for-gestational-age babies.
- Short sleep, stress, low family income with cheap energy-dense food.
Endocrine causes:
- Hypothyroidism
- Cushing syndrome (most often iatrogenic steroids)
- Growth hormone deficiency
- Pseudohypoparathyroidism
- Polycystic ovary syndrome (association in adolescent girls)
Genetic and syndromic causes:
- Prader-Willi syndrome: neonatal hypotonia and feeding difficulty, then hyperphagia and obesity, short stature, small hands and feet, hypogonadism, learning difficulty.
- Laurence-Moon-Bardet-Biedl syndrome: obesity, retinitis pigmentosa, polydactyly, hypogonadism, learning difficulty, renal problems.
- Single-gene defects (leptin, MC4R): severe early-onset obesity with intense hunger.
Others: hypothalamic damage (tumour such as craniopharyngioma, surgery, infection), drugs (steroids, sodium valproate, some antipsychotics), immobility (cerebral palsy, spina bifida).
Simple versus pathological obesity
| Feature | Simple obesity | Endocrine obesity | Syndromic obesity |
|---|---|---|---|
| Height | Tall for age | Short, slow velocity | Often short |
| Bone age | Advanced | Delayed | Variable |
| Development | Normal | Usually normal | Delayed, learning difficulty |
| Other | Family history; early puberty | Goitre (hypothyroidism), striae, moon face and hypertension (Cushing) | Dysmorphism, hypogonadism, polydactyly, eye signs |
An obese child who is tall is very likely to have simple obesity. An obese child who is short or growing slowly needs tests for hypothyroidism, Cushing syndrome and GH deficiency.
"Tall and fat: food. Short and fat: hormones."
Clinical features and complications
Examination: weight, height, BMI centile, blood pressure (correct cuff size), waist, fat distribution, acanthosis nigricans (velvety dark skin on neck and axillae), striae, hirsutism and acne, goitre, hepatomegaly, joint and gait problems, dysmorphic features, pubertal stage.
| System | Complications |
|---|---|
| Cardiovascular | Hypertension, dyslipidaemia (high LDL and triglycerides, low HDL), left ventricular hypertrophy, early atherosclerosis and coronary disease in adult life |
| Metabolic and endocrine | Insulin resistance, acanthosis nigricans, impaired glucose tolerance, type 2 diabetes, PCOS in girls, early puberty in girls |
| Respiratory | Obstructive sleep apnoea (snoring, daytime sleepiness), worse asthma, obesity hypoventilation |
| Gastrointestinal | Fatty liver (NAFLD) with raised ALT, gallstones, gastro-oesophageal reflux, constipation |
| Orthopaedic | Slipped capital femoral epiphysis (limp, hip or knee pain), tibia vara (Blount disease), flat feet, joint pain |
| Neurological | Idiopathic intracranial hypertension (headache, papilloedema) |
| Psychosocial | Bullying, low self-esteem, depression, eating disorders, poor school performance |
An obese adolescent with knee pain and a limp may have a slipped capital femoral epiphysis. Always examine the hip, because hip pain is often referred to the knee.
Investigations
Choose tests by age, severity, family history and findings.
| Purpose | Tests |
|---|---|
| Measure and classify | Weight, height, BMI plotted on a centile chart, waist circumference, BP |
| Screen for complications | Fasting glucose and/or HbA1c, fasting lipid profile, liver function tests (ALT); consider sleep study if snoring with daytime sleepiness |
| Look for a cause (when short, slow-growing, dysmorphic or delayed) | Thyroid function (especially if weight rises faster than height), cortisol studies for Cushing syndrome, bone age X-ray, karyotype or genetic tests (Prader-Willi), MRI brain if hypothalamic cause suspected |
| Other | Hip X-ray if limp; ovarian ultrasound and androgens if PCOS suspected |
Management
The aim in a growing child is often weight maintenance (so BMI falls as the child grows taller) rather than rapid loss; adolescents with severe obesity may need gradual weight loss. Treatment is family-based and multidisciplinary.
Dietary
- Balanced, regular meals with fruit, vegetables, whole grains, protein and dairy.
- Cut sugary drinks, juices and fast food; water instead.
- Sensible portion sizes; eat together as a family at the table, without screens.
- Do not force a child to eat, and do not use food as a reward.
- No crash diets in growing children; refer to a dietitian where possible.
Physical activity and behaviour
- Physical activity for more than 1 hour a day (Nelson), with active play and sport, walking or cycling to school, using stairs.
- Limit screen time to under 1-2 hours a day (Nelson), with no television in the bedroom.
- Behaviour change: set small goals, self-monitoring, praise, change the family environment (what food is in the house).
- Improve sleep routines.
- Treat complications: hypertension, diabetes, sleep apnoea, psychological support.
Pharmacological and surgical
- Drugs are not first-line; they are reserved for adolescents with severe obesity or serious complications who have not responded to lifestyle measures, under specialist care.
- Bariatric surgery is controversial in young people; in severely obese adolescents it gives significant weight loss and fewer comorbidities, but long-term safety data are limited (Nelson).
- Treat any underlying cause (thyroxine for hypothyroidism, stopping or reducing steroids where possible).
Prevention
- Promote breastfeeding; avoid overfeeding formula.
- Healthy eating from weaning onwards; avoid sweets, juices and soda.
- Encourage active play; limit screens.
- Growth monitoring with BMI plotting to catch rising centiles early.
- School-based nutrition education and physical activity.
- Parents as role models.
Expect: BMI formula and why child BMI is plotted on centile charts; overweight at the 85th-95th centile and obesity at the 95th or above (or WHO above +1 and +2 SD); simple obesity with tall stature and advanced bone age versus endocrine obesity with short stature and delayed bone age; hypothyroidism, Cushing syndrome and GH deficiency; Prader-Willi and Laurence-Moon-Bardet-Biedl syndromes; complications such as hypertension, type 2 diabetes, acanthosis nigricans, fatty liver, obstructive sleep apnoea and slipped capital femoral epiphysis; screening tests; lifestyle as first-line treatment and the limited role of drugs.
Quick revision
- BMI = kg ÷ m²; plot on BMI-for-age chart.
- Overweight 85th to under 95th centile; obese 95th or above.
- Simple obesity: tall, advanced bone age, normal development.
- Short and obese: think hypothyroidism, Cushing, GH deficiency.
- Obese with delay and dysmorphism: Prader-Willi, Bardet-Biedl.
- Complications: hypertension, dyslipidaemia, type 2 diabetes, acanthosis, NAFLD, gallstones, OSA, SCFE, depression.
- Tests: fasting glucose or HbA1c, lipids, ALT; thyroid and cortisol if growth is poor.
- Treatment: family-based diet, activity, less screen time; drugs only for selected adolescents.
Written by The House Job from standard references (Basis of Paediatrics by Pervez Akbar; Nelson Essentials of Paediatrics; Park's Preventive and Social Medicine).
FAQ
How is obesity defined in a child?
By BMI-for-age: the 95th centile or above is obese and the 85th to under 95th is overweight, using age- and sex-specific charts.
Why is short stature in an obese child important?
Simple obesity usually makes children taller; an obese child who is short or growing slowly needs tests for hypothyroidism, Cushing syndrome and growth hormone deficiency.
What is acanthosis nigricans a sign of?
Velvety dark skin on the neck or axillae marks insulin resistance and raised risk of type 2 diabetes.
Are drugs used for obese children?
Rarely. Lifestyle change is first-line; more aggressive treatment, including drugs or bariatric surgery, is kept for selected adolescents with severe obesity or complications under specialist care.