Produced by the Royal College of Physicians of Edinburgh and Royal College of Physicians and Surgeons of Glasgow

Obesity in childhood – much more than a cosmetic problem

  • Dr DC Wilson, Senior Lecturer in Paediatric Gastroenterology & Nutrition, Department of Paediatric Gastroenterology & Nutrition, Royal Hospital for Sick Children, Edinburgh, and Child Life and Health, Department of Reproductive and Developmental Sciences, University of Edinburgh, Edinburgh, Scotland
  • Dr JJ Reilly, Reader in Paediatric Energetics, Department of Human Nutrition, Royal Hospital for Sick Children, Glasgow, and Division of Developmental Medicine, University of Glasgow, Glasgow, Scotland


Childhood obesity is on the increase. Is it simply a cosmetic problem or should we be more concerned about the effects of obesity on children’s physical and psychological health? Dr David Wilson and Dr John Reilly provide an overview of childhood obesity and the extent of the problem.

Key Points

  • The importance of obesity in childhood and adolescence is now recognised, but diagnosing it accurately is more difficult than in adults. The Body Mass Index (BMI) used to diagnose adult obesity is a useful tool, but as children’s bodies are still developing this needs to be adjusted for age and sex when using it for children.
  • In the UK, about 6% of 6 year old children and about 17% of 15 year old adolescents are obese, making obesity the most common disorder in this age group.
  • Psychological ill-health is the most common consequence of obesity in childhood and adolescence. Persistence into adulthood and associations such as hyperlipidaemia (high concentrations of blood fats), high blood pressure, fatty liver and diabetes mellitus (Type 1 diabetes) have serious implications for long-term health.
  • Good studies on the prevention and treatment of childhood obesity are not yet available, but increased physical activity, dietary improvement and family help are central to current treatment.

Declaration of interests: None declared.

Childhood obesity in context

There has been much publicity about the health consequences of obesity in adult life in recent years, but there is less appreciation of the issues surrounding obesity in children and adolescents. There is a widespread perception that childhood obesity is largely a cosmetic problem, with only minor clinical effects. We were involved in the publication of a SIGN guideline in April 2003, entitled Management of Obesity in Children and Young People.1 The reasons for the production of the guideline were various: the lack of any evidence-based guideline on childhood obesity; the fact that diagnosis of obesity in childhood is less robustly performed than for adults, and therefore a wide variation in practice occurs; and the mislabelling of some large children as obese, with needless further referral and treatment, while some very obese children are not recognised, nor have appropriate referral or treatment. The rise in the prevalence of childhood obesity in the UK has been appropriately labelled an epidemic,2 and it continues to this day. The adverse consequences of childhood obesity are increasingly recognised, as is the tendency for childhood obesity to persist into adult life. Despite its rapid rise in prevalence, there have been few prevention trials of childhood obesity, and treatment of childhood obesity has had only limited success, resulting in a negative approach to treatment strategies.

Obesity in children is different from obesity in adults in various ways. The most obvious difference is that children and adolescents need to grow - during puberty, adolescents will double their weight and increase their height by 20%. This will have consequences for the diagnosis of childhood obesity, and also the management strategies for prevention and treatment of obesity in childhood. In adulthood, obesity is simply expressed as body mass index (BMI - weight in kilograms divided by height in metres squared). For example, a BMI of 26-30 kg/m2 is considered overweight, a BMI of 30-40 is considered obese, and a BMI greater than 40 is considered morbid obesity. Given the variation in growth throughout childhood, such a simple expression of obesity, unrelated to age, sex or ethnic background, is not possible. Regarding intervention, over-enthusiastic management may result in restriction of dietary energy, and could compromise normal growth and development. Unlike treatment of adult obesity, weight maintenance is therefore often a suitable goal for children.

Clinical nutrition assessment in childhood and adolescence revolves around energy balance - energy intake (food) minus energy outputs (resting metabolic rate plus activity). In contrast to adult life, where balance should be zero, children need a small continuing positive energy balance to support normal growth. An excess continuing positive balance of energy will lead to excess stores of energy, and thus obesity. It is not only fat which accumulates, but also excess lean body mass. The sources of chronic energy positive balance leading to obesity are increased energy intake and reduced energy expenditure, by either lack of physical activity or an increase in sedentary behaviour. This simple energy balance equation is poorly understood by the families of these children, who often believe their children have metabolic problems.

Definition of childhood obesity

Subjective assessment of childhood obesity has been shown in both clinical practice and publications to be inadequate, and therefore we need to perform objective assessment. Weight itself is an inadequate measure, given its relation to height, but BMI has been shown in childhood not only to screen for excess fatness, but also to be related to morbidity.1 This makes it an excellent choice of instrument for the definition of childhood obesity. BMI changes with age and differs between the sexes, so age and sex-specific centile charts are needed for childhood and adolescence, with use of cut-off levels. There is widespread support for the use of BMI in childhood,1 using the UK 1990 Growth Reference Charts.3 High cut-off levels of BMI centile have a low false-positive rate, so they do not misclassify children who are merely ‘big’ or ‘muscular’, but they have a more modest false-negative rate. This means that there are children who are falsely labelled as non-obese with a BMI less than, for example, the 90th centile. Recent work has shown that the BMI centile can also be used for the diagnosis of undernutrition in epidemiological and clinical practice.4

Prevalence of obesity

In the UK, the adult obesity epidemic began in the late 1970s whereas work by various authors has suggested that it probably started ten years later in children. Cole et al.3 collected growth data for children and teenagers in the UK in 1990, and published these in 1995. We therefore use these UK 1990 nationally representative data for our definitions of overweight and obesity. The Health Survey for England4 was a nationally representative sample which showed that in 1996 the prevalence of obesity (defined as BMI >95th centile for age and sex) was nearly 10% at six years of age, 12% at ten years of age, and 17% at 15 years of age. This has now been replicated in multiple other cohort and cross-sectional surveys.1 In Scotland, data from National Child Health Surveillance Programme in 1999 showed that 9% of children in the first year of primary school were obese (BMI >95th percentile of UK 1990 reference data) and this had risen to 16% at age 15 years.4 It can therefore be truly stated that obesity is the most common disorder of childhood and adolescence. Epidemiological studies have been less clear at finding high-risk groups in the UK for obesity. There is a definite link with socio-economic deprivation in Scotland.5 The issue of whether breast feeding is protective against later development of obesity remains a controversial area.6

Consequences of obesity in childhood

The answer to the question of ‘does childhood obesity matter?’ is that it does, both in the short term (for the child) and the long term (in adulthood). The evidence has recently been appraised and summarised in a systematic review.7 The most common side effect is psychological morbidity; the major work on psychological ill-health in childhood obesity has come from North America, and adequate research in the UK has not been performed. Very importantly, there is an increase in a cluster of cardiovascular risk factors, such as hyperlipidaemia, high blood pressure, abnormalities in left ventricular mass, hyperinsulinaemia, and prevalence of Type II Diabetes.1 7 Links to the development of asthma have been recognised, and rarer complications occur, such as orthopaedic problems and development of fatty liver.7 The consequences of childhood obesity for adult life are persistence of obesity, significant increase in cardiovascular risk factors, socio-economic effects and long-term morbidity and mortality.7

Prevention, treatment and management of childhood obesity

The literature on prevention and treatment of childhood obesity has been reviewed recently both in our SIGN guideline1 and in a pair of Cochrane reviews.8 9 The disappointing outcome is that there have been few randomised controlled trials (RCTs), and most of these have major methodological deficiencies. Only one high-quality RCT has been identified for prevention of childhood obesity.1 No high-quality RCTs have been identified for treatment of childhood obesity, and there is no evidence at all on drug therapy, surgery or residential treatments.1 Despite this gloomy literature review, we know that there are currently well-designed RCTs being performed in Scotland. MAGIC (funded by the British Heart Foundation and Glasgow City Council) is a prevention trial of childhood obesity in three to five-year-old children in nursery schools in Glasgow, and is a cluster RCT of 580 children which targets activity and inactivity. SCOTT (funded by the Scottish Executive) is an RCT of 140 primary-school-aged children in Central Scotland, which targets increasing activity, reducing inactivity, plus diet.

Given the lack of evidence base, we have adopted consensus criteria for management of the obese child.1 We have concluded that complex interventions may be the best bets, with reduction in sedentary behaviour, increased lifestyle physical activity, a dietary approach, and family involvement.1 There is also a strong argument that childhood obesity is a societal problem, rather than one that we can expect individual children and their parents to solve.10 Useful resources are available for further reading, such as the SIGN guideline,1 Cochrane reviews8, 9 and the RCPCH Guide to Treatment of Obesity in Primary Care.11


  1. Scottish Intercollegiate Guidelines Network (SIGN). Management of obesity in children and young people. A national clinical guideline. Edinburgh: SIGN, 2003.
  2. Reilly JJ, Dorosty AR. Epidemic of obesity in UK children. Lancet 1999; 354:1874-5.
  3. Cole TJ, Freeman JV, Preece MA. Body mass index reference curves for the UK, 1990. Arch Dis Child 1995; 73:25-9.
  4. Armstrong J, Reilly JJ. The prevalence of obesity and undernutrition in Scottish children: growth monitoring within the Child Health Surveillance Programme. Scott Med J 2003; 48:32-7.
  5. Armstrong J, Dorosty AR, Reilly JJ et al. Coexistence of social inequalities in undernutrition and obesity in preschool children: population based cross sectional study. Arch Dis Child 2003; 88:671-5.
  6. Li L, Parsons TJ, Power C. Breast feeding and obesity in childhood: cross sectional study. BMJ 2003; 327:904-5.
  7. Reilly JJ, Methven E, McDowell ZC et al. Health consequences of obesity. Arch Dis Child 2003; 88:748-52.
  8. Campbell K, Waters E, O’Meara S et al. Interventions for preventing obesity in childhood. Cochrane Database Syst Rev 2002; (3):CD001872 (review).
  9. Summerbell C, Kelly S, Waters E et al. Interventions for treating obesity in childhood. Cochrane Database Syst Rev 2003; (2):CD001871 (review).
  10. Gibson P, Edmunds L, Haslam DW et al. An approach to weight management in children and adolescents (2-18 years) in primary care.
  11. Schwartz MB, Puhl R. Childhood obesity: a societal problem to solve. Obesity Rev 2003; 4:57-71.