Obesity in children and young people: a crisis in public health

Ten per cent of the world's school-aged children are estimated to be carrying excess body fat (Fig. 1), with an increased risk for developing chronic disease. Of these overweight children, a quarter are obese, with a significant likelihood of some having multiple risk factors for type 2 diabetes, heart disease and a variety of other co-morbidities before or during early adulthood. The prevalence of overweight is dramatically higher in economically developed regions, but is rising significantly in most parts of the world. Prevalence of overweight and obesity among school-age children in global regions. Overweight and obesity defined by IOTF criteria. Children aged 5–17 years. Based on surveys in different years after 1990. Source: IOTF (1). In many countries the problem of childhood obesity is worsening at a dramatic rate. Surveys during the 1990s show that in Brazil and the USA, an additional 0.5% of the entire child population became overweight each year. In Canada, Australia and parts of Europe the rates were higher, with an additional 1% of all children becoming overweight each year. The burden upon the health services cannot yet be estimated. Although childhood obesity brings a number of additional problems in its train – hyperinsulinaemia, poor glucose tolerance and a raised risk of type 2 diabetes, hypertension, sleep apnoea, social exclusion and depression – the greatest health problems will be seen in the next generation of adults as the present childhood obesity epidemic passes through to adulthood. Greatly increased rates of heart disease, diabetes, certain cancers, gall bladder disease, osteoarthritis, endocrine disorders and other obesity-related conditions will be found in young adult populations, and their need for medical treatment may last for their remaining life-times. The costs to the health services, the losses to society and the burdens carried by the individuals involved will be great. The present report has been written to focus attention on the issue and to urge policy-makers to consider taking action before it is too late. Specifically, the report: reviews the measurement of obesity in young people and the need to agree on standardized methods for assessing children and adolescents, and to compare populations and monitor trends; reviews the global and regional trends in childhood obesity and overweight and the implications of these trends for understanding the factors that underlie childhood obesity; notes the increased risk of health problems that obese children and adolescents are likely to experience and examines the associated costs; considers the treatment and management options and their effectiveness for controlling childhood obesity; emphasizes the need for prevention as the only feasible solution for developed and developing countries alike. This document reflects contributions from experts working in a wide range of circumstances with a diversity of approaches, but with many shared opinions. The report has been endorsed by the Federation of International Societies for Paediatric Gastroenterology, Hepatology and Nutrition (FISPGHAN) and the International Paediatric Association (IPA). Health professionals are aware that the rising trends in excess weight among children and adolescents will put a heavy burden on health services (for example, 10% of young people with type 2 diabetes are likely to develop renal failure by the time they enter adulthood, requiring hospitalization followed by life-long dialysis treatment (2). Health services, especially in developing countries, may not easily bear these costs, and the result could be a significant fall in life expectancy. In industrially developed countries, children in lower-income families are particularly vulnerable because of poor diet and limited opportunities for physical activity. There may also be an ethnic component; for example, in the USA the prevalence of overweight among children aged 4–12 years rose twice as fast in Hispanic and African–American groups compared with white groups over the period 1986–1998 (3). In developing nations child obesity is most prevalent in wealthier sections of the population. However, child obesity is also rising among the urban poor in these countries, possibly due to their exposure to Westernized diets co-inciding with a history of undernutrition. Such rapid changes in the numbers of obese children within a relatively stable population indicate that genetic factors are not the primary reason for change. Some migration of populations may account for a proportion of the epidemic, but cannot account for it all. Although studies of twins brought up in separate environments have shown that a genetic predisposition to gain weight could account for 60–85% of the variation in obesity (4), for most of these children the genes for overweight are expressed where the environment allows and encourages their expression. These obesity-promoting environmental factors are sometimes referred to as ‘obesogenic’ (or ‘obesigenic’). Put graphically, a child's genetic make-up ‘loads the gun’ while their environment ‘pulls the trigger’ (5). A genetic predisposition to accumulate weight is a significant element in the equation, but its importance might best be viewed from another perspective: the genes that predispose for obesity are likely to be commonplace, with only a small proportion of children able to resist gaining weight in an obesogenic environment. The changing nature of the environment towards greater inducement of obesity has been described in WHO Technical Report (6) on chronic disease as follows: ‘Changes in the world food economy have contributed to shifting dietary patterns, for example, increased consumption of energy-dense diets high in fat, particularly saturated fat, and low in unrefined carbohydrates. These patterns are combined with a decline in energy expenditure that is associated with a sedentary lifestyle—motorized transport, labour-saving devices at home, the phasing out of physically demanding manual tasks in the workplace, and leisure time that is preponderantly devoted to physically undemanding pastimes.’ (pp. 1–2) This emphasis on the environmental causes of obesity leads to certain conclusions: first that the treatment for obesity is unlikely to succeed if we deal only with the child and not with the child's prevailing environment, and second that the prevention of obesity – short of genetically engineering each child to resist weight gain – will require a broad-based, public health programme. A doctor presented with an obese child must nevertheless attempt some form of remedial intervention to prevent the child's health deteriorating. The aim is to stabilize and hopefully reduce that child's accumulation of body fat, using a range of approaches discussed in the next few paragraphs. For a great majority of obese patients, the first point of contact is with a primary care physician or a public health nurse. Yet the relevant training in bariatric methods (methods related to the assessment, prevention and treatment of obesity) at the undergraduate level remains inadequate. Two national surveys in the USA conducted over 10 years, indicated that paediatric obesity was the most wanted topic for continuing medical education (7). For children who are moderately overweight, measures to prevent further weight gain, combined with normal growth in height, can be expected to lead to a decrease in BMI – i.e. children may be able to ‘grow into’ their weight. For the more seriously obese child, treatment regimes are largely palliative and designed to manage and control rather than resolve the problem. Weight control and improved self-esteem may be achieved, but the child is likely to remain seriously overweight and at risk of chronic disease throughout his or her life. The clinical management of obese children may require an extended amount of time and the assembly of a professional team including a dietitian, exercise physiologist and psychologist in addition to the physician. As paediatric obesity becomes more common, patient management may not be restricted to obesity clinics and other forms of management may be developed. Obesity clinics may be necessary for morbid obesity, but less severe forms of obesity may be better managed in primary care settings by a range of health practitioners. Obesity control in adults relies on a range of options: improvements in nutritional habits, raised levels of physical activity, behavioural modification and psychotherapy, pharmaceutical treatment and as a last resort, surgery. These options can be used alone or in combination. For children, neither surgery nor drug therapy can currently be recommended unless within a closely monitored research study (8). Of the remaining choices, no single method will ensure success, although some consensus exists. For example, reducing the time engaged in sedentary activities (such as watching television or playing computer and video games) has been shown to facilitate better treatment outcome (9). Dietary interventions in combination with exercise programmes have been reported to have better outcomes than dietary modulation alone. Exercise programmes alone without dietary modification are unlikely to be effective, because increased energy expenditure is likely to be matched by increased energy intake (10). A whole-family approach also appears vital, with several studies showing that outcomes are improved if the parents are engaged in the process, or even are the key instigators of the process, at least for younger children (11). Very strict dietary limitations were reported to have better short-term results than moderate dietary limitations. However, strictly modified diets cannot be maintained for long periods of time. More marked rebound effects are observed after the discontinuation of strict diets than after moderate dietary modifications. Two additional concerns regarding strict dietary limitations are: (1) the risk of not meeting basic nutrient requirements and thus adversely affecting growth; and (2) the risk of inducing adverse psychological effects, including appetite or eating disorders, feelings of stigmatization, anxiety and low self-esteem, especially if the intervention is not successful or the child has prior psychological problems (12, 13). Many questions regarding what constitutes the best treatment remain unanswered: there have been few sufficiently large multicentre clinical trials to test the efficacy and safety of well-defined obesity treatment programmes. Such trials may reveal which non-pharmacological and non-surgical interventions can help manage obesity over the long term. Losing weight over the short term, but then experiencing a rebound gain in weight, remains the usual experience for the majority of obese children and adolescents. The importance of further research cannot be over stated, but it is not uncommon for research and treatment to compete for limited financial resources, with research frequently being more successful in securing financial support. The lack of paediatric obesity clinics at many well-respected academic institutions illustrates this point. If the current approach to treatment is largely aimed at bringing the problem under control, rather than effecting a cure, and if this aim is only successful when a multi-disciplinary and intensive regimen is mounted, then managing the obesity epidemic will be vastly expensive and probably unaffordable for most countries. Pharmaceutical approaches may assist, but cannot replace, the multi-disciplinary management of obesity. Prevention is the only feasible option and is essential for all affected countries. Yet effective techniques for prevention have also proved elusive. Programmes to prevent obesity in children may start by identifying those children at greatest risk, but there are problems with this approach. Although screening for obesity potential may help target resources where they are most needed, such screening also creates stigma among the children identified if they are singled out for special attention. Furthermore, genetic studies suggest that most children are at risk of weight gain, and that strategies to prevent obesity in a child population – such as encouraging healthful diets and plentiful physical activity – will benefit the health of all children, whether at risk of obesity or not. The most logical settings for preventive interventions are school settings and home-based settings. A number of interventions have been tried at these levels, and these are reviewed in the present report, but success has been hard to demonstrate. A Cochrane review of those trials of sufficient duration to detect the effects of intervention concluded that there was little evidence of success (14). It suggested that a more reliable evidence base is needed in order to determine the most cost-effective and health promoting strategies that have sustainable results and can be generalized to other situations. As shown in the present report, there are several examples of interventions designed to prevent the rising levels of obesity – such as the school-based ‘Trim and Fit’ programme in Singapore and the ‘Agita Sao Paulo’ programme in Sao Paulo, Brazil. Favourable outcomes have been shown with small-scale interventions, modifying children's TV watching behaviour and promoting consumption of healthier foods by establishing a price differential. Although the beneficial results of such interventions may be detectable and significant, they are small compared with the size of the problem. Moreover, the improvements tend to decline after the intervention ends. It must be concluded that interventions at the family or school level will need to be matched by changes in the social and cultural context so that the benefits can be sustained and enhanced. Such prevention strategies will require a co-ordinated effort between the medical community, health administrators, teachers, parents, food producers and processors, retailers and caterers, advertisers and the media, recreation and sport planners, urban architects, city planners, politicians and legislators. This report highlights the underlying social changes that have led to rising levels of obesity in both the adult and child populations. These underlying factors, as listed below, are often a part of, or a consequence of social development and urbanization. Such development based on economic growth to enhance consumption is generally regarded in a positive light and, especially in developing countries as they emerge from poverty, may be aspired to. Increase in use of motorized transport, e.g. to school. Increase in traffic hazards for walkers and cyclists. Fall in opportunities for recreational physical activity. Increased sedentary recreation. Multiple TV channels around the clock. Greater quantities and variety of energy dense foods available. Rising levels of promotion and marketing of energy-dense foods. More frequent and widespread food purchasing opportunities. More use of restaurants and fast food stores. Larger portions of food offering better ‘value’ for money. Increased frequency of eating occasions. Rising use of soft drinks to replace water, e.g. in schools. Changes in these social trends may require increased awareness by countries of the health consequences of the pattern of consumption as the first step in a strategy to promote healthier diets and more active lives. Several authors 15-18) have suggested that efforts to prevent obesity should include measures involving a wide range of social actions, such as: public funding of quality physical education and sports facilities; the protection of open urban spaces, provision of safer pavements, parks, playgrounds and pedestrian zones, creation of more cycling paths; taxes on unhealthy foods and subsidies for the promotion of healthy, nutritious foods; dietary standards for school lunch programmes; elimination or displacement of soft drinks and confectionery from vending machines in schools and offering healthier choices (i.e. low-fat dairy products, fruits and vegetables); clear food labelling and controls on inconsistent health messages; controls on the political contributions given by the food industry; restrictions or bans on the advertising of foods to children; limits on other forms of marketing of foods to children; assessment of food industry initiatives to improve formulations and marketing strategies. It is clear from these suggestions that policies and actions will be needed at a variety of levels, some local and individually based, some national or internationally based. All of them will require the support and involvement of departments across the broad range of government and may include education, social and welfare services, environment and planning, transport, food production and marketing, advertising and media, and international trading and standard-setting bodies. Obesity prevention will involve work at all levels of the obesogenic environment. As Fig. 2illustrates, attempts to improve the environment at one level, for example the school, may be undermined by a failure to improve the environment at another level, be it below in the home, or above in the social and cultural context involving food marketing and advertising, lost recreational facilities or unsafe streets. The opportunities for influencing a child's environment. Children are vulnerable to the social and environmental pressures that raise the risk of obesity. Although they can be encouraged to increase their self-control in the face of temptation, and although they can be given knowledge and skills to help understand the context of their choices, children cannot be expected to bear the full burden of responsibility for preventing excess weight gain. The prevention of childhood obesity requires: improving the family’s ability to support a child in making changes, which in turn needs support from the school and community, for example . . . ensuring the school has health-promoting policies on diet and physical activity, and that peer group beliefs are helping the child, which in turn requires that . . . the cultural norms, skills and traditional practices transmitted by the school are conducive to health promotion, and that the community provides a supportive environment, such as . . . neighbourhood policies for safe and secure streets and recreation facilities, and ensuring universal access to health-enhancing food supplies, which in turn requires that . . . authorities at municipal, and regional level are supporting such policies, e.g. for safe streets and improved food access through appropriate infrastructure, and that . . . national and international bodies that set standards and provide services are encouraging better public health, and commercial practices consistently promote healthy choices, which in turn may require . . . legislative and regulatory support to ensure that strategies for obesity reduction are fully resourced and implemented, and appropriate control measures are enforced, and that these are not contradicted by other government policies, and that . . . government and inter-governmental activities in all departments, including education, agriculture, transport, trade, the environment and social welfare policies are assessed for their health impact, and Government food purchases, e.g. for departmental staff, for the military, police, prisons, hospitals and schools and other agencies involved in public sector supply contracts are consistent with health and nutrition policies. The present report is primarily addressed to health professionals, social scientists and others in a position to influence policy at national and international level, by providing a background to the problems and an indication of the policies needed to tackle them. It is written in the context of the World Health Organization's work on the prevention of nutrition-related chronic diseases and the development of strategies to promote physical activity and healthy diets. The WHO's consultation document (6) recommends the development of multi-sectoral strategies, with health ministries convening with other ministries and stakeholders to develop relevant policies, programmes and regulations. The consultation document calls for positive action, such as measures to support the greater availability of nutrient dense foods, to reduce dependence on motorized transport, to increase access to recreation facilities and to ensure health information is widely available and easily understood, and health messages are relevant and consistent. The WHO has acknowledged the restrictions placed on countries by international agreements, such as those that regulate trade and marketing practices. The WHO can offer a leadership role in prioritizing public health when negotiating these agreements. This depends upon political pressure, which in part depends upon leadership from the medical profession and from non-governmental organizations. The present report is designed to contribute to that process. The International Obesity TaskForce calls upon the WHO to assist member countries to develop National Obesity Action Plans and to prioritize childhood obesity prevention within those plans. Examples of Action Plan priorities might be to: provide clear and consistent consumer information, e.g. on food labels; encourage food companies to provide lower energy, more nutritious foods marketed for children; develop criteria for advertising that promotes healthier eating; improve maternal nutrition and encourage breast-feeding of infants; design secure play facilities and safe local neighbourhoods; encourage schools to enact coherent food, nutrition and physical activity policies; encourage medical and health professionals to participate in the development of public health programmes. The International Obesity TaskForce is committed to supporting the WHO in developing these priorities. Tackling childhood obesity will require much imagination and perspiration, but the world's children deserve no less. Power et al. suggest that ‘an ideal measure of body fat should be accurate in its estimate of body fat; precise, with small measurement error; accessible, in terms of simplicity, cost and ease of use; acceptable to the subject; and well-documented, with published reference values’ (19). They further comment that ‘no existing measure satisfies all these criteria’. Measurement of adiposity in children and adolescents occurs in a range of settings, using a range of methods. In this section, both direct and indirect methods for assessing and evaluating fatness are described and the strengths and weaknesses of these different methods used for population and clinical judgements are analysed. Direct measures of body composition provide an estimation of total body fat mass and various components of fat-free mass. Such techniques include underwater weighing, magnetic resonance imaging (MRI), computerized axial tomography (CT or CAT) and dual energy X-ray absorptiometry (DEXA). The methods are used predominantly for research and in tertiary care settings, but may be used as a ‘gold standard’ to validate anthropometric measures of body fatness (20) (Table 1). Among the anthropometric measures of relative adiposity or fatness are waist, hip and other girth measurements, skin-fold thickness and indices derived from measured height and weight such as Quetelet's index (BMI or W H−2), the ponderal index (W H−3) and similar formulae. All anthropometric measurements rely to some extent on the skill of the measurer, and their relative accuracy as a measure of adiposity must be validated against a ‘gold standard’ measure of adiposity (Table 2). The primary purposes for defining overweight and obesity are to predict health risks and to provide comparisons between populations. Faced with a continuous distribution, criteria need to be created that define where cut-off points should occur that best fulfil these purposes. For practical reasons, the definitions have usually been based on anthropometry, with waist circumference and BMI being the most widely used both clinically and in population studies. Although not validated against health criteria, weight for height measurements have become a common means of assessing populations of children, especially those aged under 5 years, and are used to define both under- and over-nutrition. Low weight for height is termed thinness, and very low weight for height is termed wasting, usually found as a consequence of acute starvation and/or disease. A high weight for height is termed overweight and very high weight for height is termed obese. The use of weight for height has the advantage of not requiring knowledge of the child's age, which may be hard to assess in less developed areas, but it should not be used as a substitute for height for age, or weight for age, as all three measures reflect different biological processes (see Table 16 in reference 42). In 1995, the use of weight for height was recommended by WHO for children below the age of 10 years, but a WHO review found that use of the US-based National Center for Health Statistics should not be recommended especially as it did not take account of differences between breast-fed and non-breastfed children (42). The WHO may consider new reference standards based on multinational studies of breast-fed children showing healthy growth (28). The weight for height score is plotted on a chart based on a standard reference population, which gives a Z-score based on the difference between the observed value and the median reference value of a population, standardized against the standard deviation of the reference population. Thus a Z-score of 0 is equivalent to the median or 50th centile value, a Z-score of +2.00 is approximately equivalent to the 98th centile and a Z-score of +2.85 is >99th centile. The use of a weight for height Z-score (WHZ) allows a more detailed statistical description of an individual or a population, and comparison between populations can also be readily made and trends over time can be described. Besides the difficulty in choosing an appropriate reference population, however, WHZ-scores require suitable statistical skills or software programmes. In terms of defining non-overweight, overweight and obese the categories are based only on statistical convenience (e.g. WHZ > 2) rather than a known health risk. In a large-scale epidemiological study of young people aged 5–17 years, Freedman et al. showed that central fat distribution (particularly as assessed by waist circumference) was associated with an adverse lipid profile and hyperinsulinaemia (37). A high waist circumference has also been shown to track well into adulthood (22). Although waist circumference percentile charts have been described (e.g. for the UK (43)), appropriate cut-off points for defining high or low health risks have not been identified. Waist circumference may be useful in clinical practice as a means of determining a child or adolescent's response to weight control measures. In epidemiological studies, it may be used to characterize a population in terms of abdominal fat distribution and to determine the prevalence of risk factors. At present, however, waist circumference cannot be used to categorize a child as being at a high or low risk. As suggested in Table 2 above, BMI is significantly associated with relative fatness in childhood and adolescence, and is the most convenient way of measuring relative adiposity (44). BMI varies with age and gender. It typically rises during the first months after birth, falls after the first year and rises again around the sixth year of life: this second rise is sometimes referred to as ‘the adiposity rebound’. (For examples of childhood BMI curves by age and gender, see Figure 28 below.) A given value of BMI therefore needs to be evaluated against age- and gender-specific reference values. Several countries, including France, the UK, Singapore, Sweden, Denmark and the Netherlands, have developed their own BMI-for-age gender-specific reference charts using local data. In the USA, reference values published by Must et al. (45) derived from US survey data in the early 1970s, have been widely used and were recommended for older children (aged 9 years or more) by a WHO expert committee in 1995 (42). More recently, the US National Center for Health Statistics (NCHS) has produced reference charts based on data from five national health examinations from 1963–1994 (46), although to avoid an upward shift of the weight and BMI curves, data from the most recent survey were excluded for children over the age of six years (47). The advantage of using BMI-for-age charts is that a child can be described as being above or below certain centile lines (for example the 85th or 90th centile), which can be useful in a clinical setting. Data, however, are usually derived from a single reference population, and classifying an individual as overweight or obese assumes that the individual is comparable to that reference population. Furthermore, clinicians may wrongly interpret the centiles as representing an ideal population, when the figures may in fact come from a reference population with a high prevalence of obesity, such as the USA NCHS data. The NCHS documentation (46) recommends that those children with a BMI greater than or equal to the 95th percentile be classified as ‘overweight’ and those children with a BMI between the 85th and 95th percentile be classified as ‘at risk of overweight’. In some papers, US children at or above the 95th centile are referred to as ‘obese’ (18) and in others ‘obesity’ refers to US children above the 85th centile (48). As with the use of weight-for-height measures compared with standard reference populations, BMI can be compared with a reference data set and reported as Z-scores. A BMI Z-score is c