Preventing Childhood Obesity

Evidence Policy and Practice

Elizabeth Waters, Boyd Swinburn, Jacob Seidell, Ricardo Uauy, Elizabeth Waters, Jacob Seidell, Boyd Swinburn, Ricardo Uauy

• Publisher: BMJ Books
• Year: 2011
• ISBN:
  9781444359299
• Edition: 1
• Topic: Medicine
• Subtopic: Medical Theory, Practice & Reference

Obesity is one of the biggest public health challenges in the 21st century. Devising effective policy and practice to combat childhood obesity is a high priority for many governments and health professionals internationally. This book brings together contributors from around the world and showcases the latest evidence-based research on community and policy interventions to prevent unhealthy weight gain and improve the health and well-being of children. The authors highlight from the evidence available what is and what is not effective and provide recommendations on how to implement and evaluate promising interventions for obesity prevention.

This book is an essential read for all public health practitioners, early childhood professionals, health care providers and clinicians working to reduce the prevalence of childhood obesity in their communities.

PART 1

The context

This section of five chapters paints the big picture for childhood obesity prevention. The problem needs to be well articulated before the solutions, which are the focus for most of the book, can be defined. The rise in obesity has many societal and environmental drivers so the options for solutions to reduce childhood obesity must be multi-dimensional and sustained. The solutions are at once simple, from a behavioral action point of view (eating less and moving more), and highly complex, from a societal, economic and cultural point of view. The solutions must also give primacy to what should be a prevailing societal responsibility to provide safe and healthy environments for children. The human rights approach to childhood obesity, therefore, provides an important frame of reference for solutions to be developed and communicated.

The epidemiology of the childhood obesity epidemic gives us many clues about its determinants and Chapter 1, led by Tim Lobstein from the International Obesity Taskforce, plots the global trends in prevalence rates. The rise has been rapid but varied, and much of the variation in prevalence is likely to be explained by environmental and socio-cultural factors——a neglected area of obesity research. The increasing demands on pediatric health services and the tracking of obesity into adulthood, and thus the future demand on adult health services, are two enormous challenges we face. We need to look widely for the answers to the obesity epidemic and there are many valuable lessons to be learned from the successful control of other epidemics. This important evidence, which is explored in Chapter 2 by Mickey Chopra, is known to many epidemiologists and public health researchers who work across different health issues, but the lessons need to be applied systematically to obesity. The central role of policy is one crucial lesson that has yet to be well applied in obesity prevention.

Terms “life-course”, “multi-sector”, multi-strategy”, “whole-of-society” are often used to describe the approaches to obesity prevention and these are discussed in Chapter 3 by Ricardo Uauy and colleagues. What becomes an inescapable conclusion is that we cannot hope to reduce childhood obesity in the face of the continuing barrage of commercial marketing of “junk” food to children. Something must be done to reduce this overwhelming driver of obesogenic environments as a central plank of childhood obesity prevention. Taking an ethics-based, child rights approach is vital to give gravity to society’s response. It also ensures that the ethical dilemmas intrinsic to obesity prevention, such as the potential for risk and the balance between paternalism and individualism, are assessed and managed in the best interests of child health. Chapter 4, led by Marieke ten Have, and Chapter 5, led by Naomi Priest, enter this important territory and, again, food marketing to children arises as a fundamental problem.

CHAPTER 1

The childhood obesity epidemic

Tim Lobstein,¹,² Louise A Baur³ and Rachel Jackson-Leach¹

¹International Association for the Study of Obesity, London, UK

²SPRU—Science and Technology Policy Research, University of Sussex, Brighton, UK

³Discipline of Paediatrics and Child Health, University of Sydney, Sydney, Australia

Summary

• Childhood obesity can be measured in various ways, but applying a single method across all available data shows a rapid rise in the numbers of children affected.
• Very few countries have shown a reversal of this trend, but prevalence levels vary across populations, and according to social demographics.
• The rise in child obesity will almost certainly lead to a rise in adult obesity rates.
• Child obesity is a health concern itself and will increase the demand for pediatric treatment.

Introduction

In many developed economies child obesity levels have doubled in the last two decades.¹ The impending disease burden in these countries has been described by medical professionals as “a public health disaster waiting to happen”,² “a massive tsunami”,³ and “a health time-bomb”.⁴ In emerging and in less developed economies, child obesity prevalence levels are also rising,⁵ especially among populations in urban areas where there may be less necessity for physical activity, greater opportunities for sedentary behavior and greater access to energy-dense foods and beverages.

This chapter looks at the figures and predictions, and considers the implications in terms of children’s obesity-related health problems and the need for policy development for both pediatric treatment services and public health preventive action.

Measuring the prevalence of obesity

Policy-makers will need to evaluate the trends in child obesity and the success of any interventions, but they face an initial problem in agreeing a clear definition of what constitutes excess body weight in a child. Among adults, obesity is generally defined as a BMI greater than 30 kg/m², and overweight as a BMI between 25 and 30 kg/m², but for children there are difficulties in defining a single standard as normally-growing children show significant fluctuations in the relationship between weight and height. Charts showing weight, height and BMI for children by age and gender are commonly used, but with different cut-off points for overweight and obesity, such as 110% or 120% of ideal weight for height, or weight-for-height greater than 1 or 2 standard deviations above a predefined mean, or a BMI-for-age at the 85th, 90th, 95th or 97th percentiles, based on various reference populations.¹

For young children, it has been common practice to use “weight-for-height” rather than BMI. This stems from existing definitions used in the assessment of underweight and stunting, where “weight-for-age”, “height-for-age” and “weight-for-height” are used to assess infant growth. The measures are still occasionally used for assessing overweight in young children, usually by taking a value of two standard deviations (Z >+2.0) above a reference population mean as the criteria for excess weight for a given age and gender.

In recent years, BMI has been increasingly accepted as a valid indirect measure of adiposity in older children and adolescents for survey purposes,^1,6 leading to various approaches to selecting appropriate BMI cut-off values to take account of age and gender differences during normal growth.^7–12 A number of different BMI-for-age reference charts have been developed, such as those from the US National Centre for Health Statistics,⁹ the United Kingdom¹⁰ and France.¹¹

An expert panel convened by the International Obesity TaskForce (IOTF) proposed a set of BMI cut-offs based on pooled data collected from Brazil, Britain, Hong Kong, Singapore, the Netherlands and the USA. The IOTF definitions of overweight and obesity are based on BMI centile curves that passed through the adult cut-off points of BMI 25 and 30. The resulting set of age- and gender-specific BMI cut-off points for children was published in 2000.¹²

The World Health Organization (WHO) has for many years recommended using a set of cut-offs based on a reference population derived from the USA, but more recently the WHO has been reviewing their recommendations. There had been concern that the USA data included large numbers of formula-fed infants with growth patterns that differed from breast-fed infants, and which underestimated the true extent of overweight in younger children. WHO has now published a new “standard” set of growth charts for children aged 0–5 years, based on data from healthy breast-fed babies.¹³ It is unclear at this stage what BMI cut-off values should be used from this healthy population to define overweight and obesity, with both centile and Z-score options available in published tables. Further reference charts are available for children aged 5–19 years, based on a revision of US data collected in 1977 adapted to match the standards for 0–5-year-olds.

Care should be taken when looking at published prevalence figures for overweight and obesity. Some authors use “overweight” to define all members of a population above a specified cut-off, while others mean “overweight” to mean those above one cut-off but not above a higher cut-off that defines obesity. Thus, in some reports the prevalence value for “over-weight” children includes obese children and in other reports it does not. In this section “overweight” includes obese, so the term should properly be understood to mean “overweight including obese”. Readers should also note that prevalence levels using reference curves from the USA sometimes refer to “at risk of overweight” and “overweight” for the top two tiers of adiposity, and sometimes to “overweight” and “obese”.

It should also be noted that the definitions are very helpful for making comparisons between different population groups, or monitoring a population over time. However, for the clinical assessment of children, serial plotting of BMI on nationally recommended BMI-for-age charts should be coupled with more careful examination of the child in order to be sure that, for example, a high BMI is not due to extra muscle mass or to stunted linear growth.

In this chapter the prevalence levels will be based on the IOTF international classification scheme, as most survey evidence is available using this approach, and the results tend to be more conservative than some other approaches.¹

Prevalence levels

Policy-makers face a second hurdle in understanding the circumstances surrounding obesity in children and adolescents, namely, a lack of representative data on what is happening in the population that is of interest. Only in a few countries are children monitored routinely and data on their nutritional status gathered, analysed and reported consistently.

Even where data are available, they need to be examined carefully. Firstly, data may be collected using proper measurement procedures, or may be self-reported, but self-reported measures tend to underestimate BMI, especially among more over-weight respondents. Data may come from nationally representative surveys or from smaller surveys—for example, in the more accessible urban areas—which do not represent national populations. And, when comparing two surveys across a period of time, surveys need to be properly comparable in terms of the children’s ages, and their ethnic and socio-demographic mix.

The figures presented here are based on the latest and most reliable available, some of which were previously published in 2006 by Wang and Lobstein.⁵ Unless otherwise stated, the IOTF definitions of over-weight and obesity in childhood are used.

Global figures

Taking an estimate for the world as a whole, in 2004 some 10% of school-age children (aged 5–17) were defined as overweight, including some 2–3% who were obese. This global average reflects a wide range of prevalence levels in different regions and countries, with the prevalence of overweight in Africa and Asia averaging well below 5% and in the Americas and Europe above 20%. Projections to the year 2010 are shown in Table 1.1.

Table 1.1 Estimated prevalence of excess bodyweight in school-age children in 2010.

Source: Wang and Lobstein.

Region^a	Obese	Overweight (including obese)
Americas	15%	46%
Mid East & N Africa	12%	42%
Europe & former USSR	10%	38%
West Pacific	7%	27%
South East Asia	5%	23%
Africa	> 1%	> 5%

^aCountries in each region are according to the World Health Organization.

Region: Americas

The most comprehensive and comparable national representative data on trends in the prevalence of obesity are from the USA, where nationally representative surveys undertaken in the 1960s were followed by the series of National Health and Nutrition Examination Surveys (NHANES) from 1971 onwards. The most recent publications (for surveys conducted in 2003–2004) show that 36% of children aged 6–17 were overweight, including 13% obese. These figures are based on the international (IOTF) criteria for overweight and obesity,¹² and compare with 36% and 18% respectively using US-defined cut-offs.¹⁴

In Canada 26% of younger children and 29% of older children were found to be overweight in a 2004 survey, almost exactly double the prevalence levels found among children 25 years earlier.¹⁵ In Brazil, the prevalence of overweight among school-aged children was 14% in 1997, compared with 4% in 1974. In Chile, in 2000 the prevalence of overweight among school children was 26%.

There are few data available for schoolchildren in most other South and Central American countries, but some data have been collected for pre-school children. In Bolivia, the prevalence of overweight (defined as one standard deviation above a reference mean) was 23% in 1997, and in the Dominican Republic it was 15% in 1996. In a few countries in the region, obesity prevalence has fallen: in Columbia it fell from 5% to 3% between 1986 and 1995.

Region: Europe

A number of studies have examined childhood over-weight and obesity prevalence in European countries. The highest prevalence levels are observed in southern European countries. A survey in 2001 found that 36% of 9-year-olds in central Italy were overweight, including 12% who were obese. In 1991, 21% of school-age children in Greece were overweight or obese, whereas a decade later, in 2000, 26% of boys and 19% of girls in Northern Greece were overweight or obese, while data from Crete in 2002 show 44% of boys aged 15 years to be overweight or obese. In Spain, 35% of boys and 32% of girls aged 13–14 years were overweight in a survey in 2000.

Northern European countries tend to have lower prevalence values. In Sweden in 2000–2001, the prevalence was 18% for children aged 10 years. In the Netherlands the figures are particularly low, with only 10% of children aged 5–17 overweight, including only 2% obese, in a 1997 survey. In France, the figures are a bit higher, at 15% overweight and 3% obese in a northern French survey in 2000, and these figures appear to have remained stable, according to recent preliminary results of surveys in 2007.¹⁶ In England, prevalence rates have climbed to 29% overweight, including 10% obese, in a 2004 survey.

The reasons for a north–south gradient are not clear. Genetic factors are unlikely to be the explanation, as the gradient can be shown even within a single country, such as Italy and virtually all countries have shown a marked increase in prevalence in recent decades. A range of factors influencing regional barriers or promoters of population levels of physical activity may be important. The child’s household or family income may be another relevant variable, possibly mediated through income-related dietary factors such as maternal nutrition during pregnancy, or breast- or bottl...

Table of contents

• Cover
• Title
• Copyright page
• Preface
• Contributors
• Foreword
• Part 1: The context
• Part 2: Evidence synthesis
• Part 3: Evidence generation and utilization
• Part 4: Policy and practice
• Index