There is a great concern among both health professionals and the public about the best way of managing the current explosion in adult and adolescent obesity. In the US, the prevalence of obese teenagers between 1980 and 2007 increased from 5 to 18 %1 and the UK has seen a similar trend, especially in boys (see Figure 1). Since a substantial proportion of obese teenagers become obese adults,2,3 it seems reasonable to try and address this population, especially since there are several obesity-related health problems in childhood4 and sustained weight loss in obese adults is difficult to achieve without surgery.
No randomised controlled intervention in children has ever been shown to prevent obesity, but combined measures have shown a mild stabilisation of weight over 6–12 months.5,6 Obesity prevention strategies for children can change behaviour, but efficacy in terms of preventing obesity remains poorly understood. Children change in shape as they grow and are expected to increase in weight as they mature, so weight loss or change in body mass index (BMI) are often inappropriate goals. Weight maintenance in adolescence is often pursued as a safe, manageable and realistic aim. Other measured endpoints include waist circumference, waist to hip ratio, fat mass, measures of insulin sensitivity and cardiorespiratory exercise capacity. More recently, measures of cardiac and vascular structure and function have emerged as potential intermediate endpoints. These allow more direct assessment of the impact of weight reduction programmes on the cardiovascular system.7
Childhood Obesity and Cardiovascular Disease
Childhood Obesity and Disease in Childhood
Even during childhood, obesity leads to increases in risk factors such as high blood pressure, diabetes mellitus, hypercholesterolaemia and the metabolic syndrome,8 as well as non-cardiac sequelae that include musculoskeletal defects, non-alcoholic steatohepatitis, gallstones, increased risk from certain cancers, bullying and depression.9 There is considerable evidence that increased body weight has direct effects on vascular development, cardiac size and function, even in the absence of the above additional cardiovascular risks. Excess abdominal fat mass is associated with reduced aortic distensibility and increased pulse wave velocity.
This, coupled to the increased circulating volume that is found in obese children may well underlie the increased blood pressure seen in over 20 % of obese teenagers.10 Independently of hypertension, childhood obesity is also associated with increased left ventricular mass and eccentric left ventricular hypertrophy.11 Furthermore, autopsy studies in obese children reveal increased atherosclerotic plaque burden.7
Childhood Obesity and Adult Disease
Adolescent obesity also predicts who will be obese as adults with levels of BMI tracking into adulthood, where it is associated with atrial dilatation, reduced distal aortic distensibility, increased circulating volumes and ‘obesity cardiomyopathy’. The odds of childhood obesity persisting into adulthood are smaller in the early years compared with adolescence,12 but the long-term impacts of being overweight and obese in the first decade of life have not been fully studied. The Bogalusa Heart Study, commenced in 1972, is one of the first studies to provide prospective data through to adulthood on the impact of obesity and, based on 14,000 children, has demonstrated the manifestation of the risks of excess body weight in terms of atherosclerosis and early onset type 2 diabetes.13 More recently, large prospective studies in Europe and the USA, including national and international monitoring approaches, have been established.8 These have provided information on the problems of childhood obesity during childhood and in the future will provide longitudinal follow-up through to adulthood.
Who to Treat and What Endpoints to Use?
Defining Childhood Obesity
It is possible to take population-based approaches to weight management but more often targeted interventions are used in those who are determined to be obese. To achieve this, a clear definition of obesity is required. At present, there is no clear global consensus on the definition of childhood obesity. Children are routinely weighed and measured in infancy. Traditionally, this was to ensure that there is no ‘failure to thrive’, although the scope of malnutrition has now come to encompass overfeeding. Growth charts for boys and girls are used as the basis for most assessments, with overweight usually being >85th centile and obese >95th centile, but in clinical settings obesity is often defined as >98th centile.
The reference data may have come from a local, national or an international population.14 Use of data from the same population as a child has great inherent advantages at a local level in showing trends across time periods, but comparisons between regions or nations become difficult. In the UK, the National Child Measurement Programme has been set up in schools at reception (age 4–5) and at Year 6 (age 10–11) and uses a national reference chart from 1990 for comparison (see Figure 2), which is different from the growth charts used in the US or by the World Health Organization (WHO). Moreover, growth curves and patterns of obesity vary between races, and in an increasingly multicultural society this is important to address.15 The WHO has addressed this in redefining BMI ranges for weight in different races in adults,16 but not yet in children.
Currently, clinical assessment of childhood obesity is based on age- and sex-matched BMI calculations, although, as discussed, cut-offs for overweight and obese vary between countries. Skinfold thickness and waist circumference have been used, but are indirect measures with considerable interobserver variability and do not predict future cardiovascular risk. Direct assessment of fat mass with imaging modalities is less subjective, but not yet cost effective or practical at a population level, although increasingly used in research. Therefore, the majority of studies use a range of body size indices to try and effectively characterise degree of obesity.
Cardiovascular and other Endpoints
As one of the main goals of weight reduction is to reduce cardiovascular risk, it may also be appropriate to use non-body size endpoints to assess the efficacy of any intervention. Markers of metabolic risk are of particular interest because of the close relationship between obesity and metabolism (see Table 1). Evaluating the diet and physical activity of the child are also key parts of an assessment to determine whether there has been change in behaviour. At a basic level, weight gain is due to an imbalance between energy intake and expenditure. Diet diaries, discussion of family food shopping bills, heart rate monitors, pedometers and accelerometers have all been used in research and clinical settings, but there is no standardisation. Eating disorders are also often associated with underlying family and social problems, warranting psychosocial assessment.
As weight or BMI per se are poor measures of individual cardiovascular risk in children, there has been recent interest in the use of other markers of ‘cardiovascular health’. These include flow-mediated dilatation measured at the brachial artery, carotid artery intima-media thickness, LV mass and visceral fat mass as surrogate endpoints (see Figure 3). These are easy to measure in longitudinal studies and have been validated as predictors of future cardiometabolic risk.
What Interventions to Use?
Several diets have been tried in different settings, but the principal message is not what children should eat, but what they should not eat – high calorie beverages, refined carbohydrates, excess dietary fat and most importantly, excess portion sizes. The wider debate includes the role of the food and advertising industries in addressing children’s access to energy-dense foods (such as school-vending machines). Importantly, up to the age of 14, dietary intervention alone is not effective at weight maintenance.
Exercise and Sedentary Behaviour
Current guidelines suggest a minimum of one hour’s moderate intensity activity per day for children. Several exercise strategies in obese children have been shown to be beneficial, leading to a reduction in fat mass, lower insulin resistance and reduced blood pressure. However, formal exercise training depends entirely on the participation of the child and concordance, so the generalisability of trial data to our schools is questionable. In studies, overweight children are more likely to exercise when separated from normal thinner children. When playing with normal weight peers, overweight children expend more energy on a given locomotor activity, such as running and also suffer increased biomechanical strain. This leads to early fatigue, and they are thus less likely to fully participate. Thus, any prescribed exercise programme for obese and overweight children must be tailored to them specifically. The type of exercise that best reduces obesity is still being debated. Strength training, aerobic exercise and high intensity interval training are all beneficial in different ways. Farpour-Lambert et al.17 studied the effect of an additional 60 minutes of mixed intensity exercise on obese 6–11-year-olds over three months and found quantifiable reduction in arterial stiffness, blood pressure (7 mmHg systolic) and visceral adiposity, but BMI did not change as excess fat mass was replaced with muscle.
As well as formal exercise, the role of the physical environment in promoting or reducing activity has been studied. A recent study used GPS surveillance at five-minute intervals combined with accelerometry data in 100 children to determine where and when they were most active.18 Their findings show that children tend to be active close to home, with 63 % of strenuous physical activity occurring inside neighbourhoods. Among urban children, gardens (28 %) and the street environment (20 %) were the most commonly used environments for physical activity. Among rural children farmland (22 %) and grassland (18 %) were most frequently used. Technological developments, improved transport, urbanisation and changes in social play and interaction have created an ‘obesogenic environment’ – a child growing up in an inner city flat on a busy street with no garden is at risk from this environment and it is no surprise to find a higher prevalence of childhood obesity in urban areas compared to rural areas. To counter this, simple measures such as walking to school, limiting television viewing and enabling active play (such as youth clubs) have been successfully promoted. Indeed, interventions to reduce sedentary activity have been more successful at arresting weight gain than dietary interventions and the benefits are more sustainable in the long term.19 As with diet, the message of what not to do in terms of staying sedentary is clearer than determining exactly what to do.
Family and Behavioural Approaches
Treating obese children necessitates involvement of the family as, in practical terms, the diet of the child is dependent on the food provided by the parents or guardians. Family support also enhances and prolongs lifestyle changes that may lead to sustained weight maintenance. The child also acts as an agent of change in promoting healthier eating and more activity among other members of the family, fostering a positive cycle of health promotion.
Medical Management and Bariatric Surgery
There is only one drug available at present to obese children that may help as an adjunct to weight loss – orlistat. A randomised controlled trial in 539 obese American adolescents showed only a 0.5 kg weight gain over one year with the drug compared to a 3 kg gain with a placebo.20
Interestingly, both groups had dietary advice, behavioural therapy and a formal exercise programme and yet the placebo arm was still not successful at weight maintenance. Orlistat is safe, but up to 50 % of patients get gastrointestinal symptoms while on it, especially if they continue on a high-fat diet. Sibutramine, rimonabant and fenfluoromine have been withdrawn from use in the US and Europe due to increased risk of stroke and progressive valvular heart disease.
To date, no randomised controlled trials have addressed the long-term safety and efficacy of bariatric surgery in severely obese adolescents.21 Long-term data are needed to show safety and efficacy of surgical treatments during the period of active growth and maturation, especially as these interventions can cause micronutrient depletion and malnutrition.
Obesity is a phenotype with many interacting factors and the relative importance of each of these variables is difficult to assess. As such, it lends itself to a combined approach involving diet, exercise, behavioural support, medical therapy and surgery when warranted. As a chronic condition, the model of care should be similar to modern adult heart failure management – referral to a multidisciplinary team for thorough initial assessment and investigation, an initial plan of treatment, regular follow-up via specialist nurses and clinics, with continued focus on patient education so that the child and family learn to manage the condition independently, with expert clinical support available when needed. This is similar to paediatric asthma and diabetes management as well. Unfortunately, no European health system has yet managed to implement such a system for weight management despite promising data from pilot studies.
Politics and Awareness
The HEALTHY study was a recent large multicomponent school-based weight loss intervention in 4,603 6th grade children in the US.22 From 42 schools, 21 were randomised to have the intervention, which consisted of improved dietetics, increased physical activity, behavioural training and social marketing. The remaining 21 schools acted as controls. After two years, there was no significant difference between the two groups, but both the controls and the intervention schools had a 4 % reduction in overweight and obese pupils.
As the schools were in the same areas, this would suggest that awareness by pupils, teachers and families of the study contributed hugely to the successful reduction in obesity. Far from being a negative study, this result has renewed political and academic will to raise awareness with local and national campaigns.
Modern childhood has an inherent energy imbalance, especially in our cities. Less active play, easier commutes to school, increased car use, a lack of open spaces, coupled to easy access to energy-dense foods and larger portions has led to a surge in the prevalence of childhood obesity. These children are already at risk of metabolic syndrome, hypertension, vascular dysfunction and abnormal cardiac development, as well as other sequelae of their excess body weight. Promising data from recent intervention studies suggests changes in behaviour, body size and cardiovascular risk markers are possible. There is now a need to accelerate efforts to prevent and reverse this trend in youth. This will involve collaborations between healthcare workers, schools, politicians and policy makers,23 but, if successful, will lead to dramatic savings in future healthcare costs and burden of disease.