Children, Obesity and Exercise

Prevention, Treatment and Management of Childhood and Adolescent Obesity

Andrew P. Hills, Neil A. King, Nuala M. Byrne

• Publisher: Routledge
• Year: 2007
• Print ISBN: 9780415408844
• eBook ISBN: 9781134132263
• Edition: 1
• Topic: Education
• Subtopic: Physical Education

Throughout the developed world there is an increasing prevalence of childhood obesity. Because of this increase, and awareness of the risks to long term health that childhood obesity presents, the phenomena is now described by many as a global epidemic.

Children, Obesity and Exercise provides sport, exercise and medicine students and professionals with an accessible and practical guide to understanding and managing childhood and adolescent obesity. It covers:

• overweight, obesity and body composition;
• physical activity, growth and development;
• psycho-social aspects of childhood obesity;
• physical activity behaviours;
• eating behaviours;
• measuring children's behaviour;
• interventions for prevention and management of childhood obesity.

Children, Obesity and Exercise addresses the need for authoritative advice and innovative approaches to the prevention and management of this chronic problem.

1 Childhood obesity – an introduction

J. Yeung and A.P. Hills

Introduction

The increasing prevalence of childhood overweight and obesity is a global trend (World Health Organization, 1997) and is of concern as overweight or obese children are at a higher risk of experiencing a range of health problems in the immediate, short and long term.

Immediate health problems of overweight and obese children include social isolation and potential psychological dysfunction (Friedman, Story and Perry, 1995; Must, 1996; Must and Strauss, 1999). Young overweight children have been described by their peers as ugly, stupid, dishonest and lazy (Staffieri, 1967) and they may experience teasing and social isolation as a result (Stunkard and Burt, 1967). Such children are also at greater risk of co-morbidities than their lean counterparts. For example, children who are overweight or obese are at greater risk of asthma, and when they have it they have been shown to use more medicine (Belamarich et al., 2000; Luder, Melnik and DiMaio, 1998), wheeze more, experience more unscheduled visits to hospital (Belamarich et al., 2000) and miss more school days as a result of their asthma than lean asthmatic children (Luder, Melnik and DiMaio, 1998).

In the short term, overweight and obese children are more likely to develop certain gastrointestinal, cardiovascular, endocrine and orthopaedic problems than their lean peers that may be exacerbated in the long term. Further, overweight and obese girls are more likely to develop reproductive system abnormalities, such as early onset of puberty and menarche, and polycystic ovary syndrome (Goran, 2001; Must, 1996; Must and Strauss, 1999; Taitz, 1983).

Data from the longitudinal Bogalusa Heart Study suggest that, in the long term, cardiovascular disease risk factor prevalence increases greatly over time in overweight and obese children (Goran, 2001). In short, remaining obese from childhood through adolescence and into adulthood places the individual at a higher risk of associated morbidities (Guo and Chumlea, 1999; Magarey et al., 2003).

Aetiology of obesity

Environmental factors such as diet, physical activity and metabolic status are major contributors to obesity, and in turn are influenced by genetic traits (Weinsier et al., 1998). As a rule, excess body fatness results from a long-term imbalance between energy intake and energy expenditure (NHMRC, 1997).

Diet

The increased consumption of highly refined and often high-fat food products has been identified as a key energy intake factor contributing to overweight and obesity in adults (Popkin, 2001). In Europe and North America, simple sugars and fat account for more than half the energy intake and consumption of refined grains has mostly replaced that of whole grains (Chopra, Galbraith and Darnton-Hill, 2002). Eck et al. (1992) and Gazzaniga and Burns (1993) have reported a significant relationship between childhood obesity and the percentage of dietary intake from fat; however, a study by Wang, Patterson and Hills (2003) found no differences in the average intake of energy and fat between non-overweight and overweight or obese Australian children and adolescents. This finding is consistent with reports from other countries that suggest there has not been a concurrent increase in energy and/or fat intake with increasing obesity prevalence (Nicklas et al., 1993; Rolland-Cachera, Deheeger and Bellisle, 1996).

The apparent lack of consistency in findings for energy and fat intake in youth may be a function of the relative difficulty in accurately measuring individual intake, including reporting biases. More research is required in the area.

Physical activity

In a number of countries, including the United States, there is evidence that physical activity among youth has declined in recent decades and the corresponding increase in obesity prevalence may be the direct result of this decline (Luepker, 1999). An Australian study comparing physical activity in 10- to 11-year-old children from 1985 to 1997 also reported a decrease in physical activity (Dollman et al., 1999).

As for energy intake, the relationship between obesity and physical activity varies across studies. For example some studies (Sunnegardh et al., 1986; Waxman and Stunkard, 1980) have reported an inverse relationship between activity and adiposity levels while others have found no relationship (Saris, 1986; Wilkinson et al., 1977). Again, the measurement challenges in the physical activity area may account for the lack of definitive findings.

Metabolic factors

Weinsier et al. (1998) suggest that a number of metabolic factors have the potential to influence the onset of obesity. These include resting energy expenditure, the thermic effect of food (food- or drink-induced increase in metabolic rate), activityrelated energy expenditure and fuel utilization. However, much of the research in this area has been conducted on adults and not the childhood population.

Resting energy expenditure (REE) varies amongst individuals; however, although individual variations in REE may affect total daily energy expenditure, the variations may only have a small impact on the tendency to gain significant weight (Goran et al., 1998; Seidell et al., 1992; Weinsier et al., 1998). Similarly, while the energy expended via the thermic effect of food in obese people may be reduced (Weinsier, Bracco and Schultz, 1993), the potential weight gains are too small to be considered a likely cause of obesity. In contrast, there is widespread acceptance that the most variable component of total energy expenditure, activity energy expenditure (Carpenter et al., 1995; Goran, 1995), is a potentially significant contributor to the predisposition to obesity (Ravussin et al., 1988; Zurlo et al., 1992). The effects, if any, of fuel utilization on obesity are not established (Weinsier et al., 1998).

The impact of the environment in the promotion of childhood obesity

Despite recent advances in genetic research, genetics alone cannot explain the obesity epidemic (Hill and Peters, 1998). Although genetics may predispose some individuals to obesity and related diseases (Carmelli, Cardon and Fabsitz, 1994), this alone is not sufficient to cause the condition (Bouchard, 1995; Greenberg, 1993; Maffeis, 2000) and other determinants must be present for obesity to occur. Eaton, Konner and Shostak (1988a,b) suggest that the human gene pool has not changed substantially over the last 35,000 years but the living environment has been radically transformed, particularly in the past century in industrialized nations.

The ‘discordance hypothesis’ has been proposed to describe how the human genome, with its various susceptibilities, is more likely to express ‘diseases of civilization’ in the current environmental circumstances (Eaton, Konner and Shostak, 1988a,b). For example, today, energy-dense foods are readily available and there are commonly minimal requirements for physical activity for subsistence. The hypothesis suggests that obesity results from a mismatch between the modern lifestyle and the lifestyle for which humans, and their genes, evolved. Despite significant advances in reducing mortality related to infectious diseases, detection and treatment of many other conditions and an overall increase in longevity, a shift has occurred to an increase in chronic and degenerative diseases that are strongly associated with the western lifestyle (Popkin, 1998).

Hill and Peters (1998) suggest that the present environment promotes high energy intake and low energy expenditure. Under such circumstances, obesity occurs more frequently because, whereas the body has excellent physiological defence mechanisms that protect against the depletion of body energy stores, it has weak defence mechanisms to prevent the accumulation of excess energy stores when food is abundant. In addition, changes in social eating behaviours, enticing food advertisements and larger food portion sizes may override the normal leptin-induced satiety, and thereby cause excess weight gain.

The term ‘obesogenic’ has been coined to describe the current environmental circumstances. The obesogenicity of an environment is defined as ‘the sum of influences that the surroundings, opportunities, or conditions of life have on promoting obesity in individuals or populations’ (Swinburn, Egger and Raza, 1999: 564).

Behavioural determinants of obesity and the effect of the environment

Despite the general consensus that environmental factors are likely to be important in influencing factors such as energy intake, physical activity levels and ultimately body weight, the empirical evidence of a relationship between specific environmental exposures and obesity is poor (Crawford and Ball, 2002). There is a large range of environmental factors that could potentially increase the likelihood of weight gain and thus risk of obesity (Booth et al., 2001; French, Story and Jeffery, 2001), but these environmental influences must be mediated by the population’s eating and physical activity behaviours (i.e. through energy intake and energy expenditure) (Crawford and Ball, 2002). These behaviours are critically important since they form the interface between human biology and the environments to which the population is exposed (Crawford and Ball, 2002). In short, the development of obesity may be better understood with knowledge of the population’s eating and physical activity behaviours, the determinants of these behaviours, and how they might be influenced (Law, 2001).

From an epidemiological perspective, the behaviours themselves should be focused on, rather than the disease or health condition (Mason and Powell, 1985). Additionally, there should be an examination of their psycho-social and social–ecological antecedents (Raymond, 1989). In relation to obesity, it is important to acknowledge that the environment is but one source of influence, albeit potentially potent (Booth et al., 2001; French, Story and Jeffery, 2001; Kumanyika et al., 2002).

The environment is one of a number of factors that influence obesity development and also affect people’s behaviours. Hill and Peters (1998) suggest that the environment’s contribution to obesity should be thought of in terms of how it contributes to the frequency of behaviours that increase or decrease the risk of a positive energy balance. For example, parents influence the nature and amount of physical activity in which children engage. Kohl and Hobbs (1998) concluded that parental influence on physical activity among children is most likely an interaction of direct and indirect factors. Parents may have a direct influence by providing an environment that nurtures physical activity in the child, and have indirect influence through modelling of physical activity participation. Young children (four to seven years of age) whose parents were physically active were nearly six times as likely to be physically active as peers of whom neither parent was physically active (Moore et al., 1991). Therefore, parents who provided physical activity-promot-ing environments, and who were physically active themselves, influenced their children to adopt a significantly higher frequency of physical activity behaviours (and the likelihood of a decreased risk of positive energy balance) compared with children with less physical activity-stimulating environments.

Obesity may thus be viewed as a natural response to the environment. However, within any given environment, an individual has a certain probability of becoming obese but not a certainty. Some individuals resist gaining weight and becoming obese in unsupportive environments by maintaining a pattern of healthy behaviours (Hill and Peters, 1998). Therefore, some individuals are susceptible to the obesogenic environment whilst others are able to resist it.

In summary, obesity is the consequence of an energy imbalance, with energy intake exceeding energy expenditure. Although the expression of certain genes might increase one’s vulnerability to obesity, other determinants, a mixture of environmental and behavioural, must be present for obesity to occur.

Necessary modifications to the environment to afford a shift in activity levels

From research evidence to date, Campbell et al. (2002) believe that childhood obesity prevention strategies should encourage a reduction in sedentary behaviours with concurrent increases in physical activity. Advances in technology and transportation have reduced the need for physical activity in daily life (Hill and Peters, 1998), and the appeal of television, electronic games and computers has increased the time spent in sedentary pursuits among both children and adults. If a low level of physical activity energy expenditure is not matched with a correspondingly lower daily energy requirement, weight gain is the likely outcome.

An important challenge is to provide all children with an environment conducive to regular physical activity. This is particularly difficult given the diversity of urban and rural settings and mix of socioeconomic determinants. For example, a study of a multiethnic sample of youth indicated that racial/ethnic disparities in exercise levels were mediated by disparities in access to exercise facilities and programmes (Garcia et al., 1995). A parallel challenge is to encourage all children to be physically active irrespective of size, shape and physical ability (Hills and Cambourne, 2002).

Investigations using self-report and/or more objective measures of physical activity have identified the following correlates of physical activity behaviour: physical activity self-efficacy (Trost et al., 1996, 1997, 1999); enjoyment (Borra et al., 1995; Stucky-Ropp and DiLorenzo, 1993); parental influences (Moore et al., 1991; Sallis et al., 1992); attitudes or beliefs about physical activity outcomes (Craig, Goldberg and Dietz, 1996; Theodorakis et al., 1991; Trost et al., 1999); access to equipment and programmes (Pate et al., 1997; Trost et al., 1997); social norms regarding physical activity (Trost et al., 1999); involvement in communitybased physical activity organizations (Trost et al., 1999); and time spent outdoors (Trost et al., 1999).

The most salient predictor of exercise behaviour was child enjoyment of Yeung and Hills physical activity (Stucky-Ropp and DiLorenzo, 1993). Poor physical activity experiences may be a s...

Table of contents

• Cover Page
• Title Page
• Copyright Page
• Figures
• Tables
• Boxes
• Contributors
• 1 Childhood Obesity – An Introduction
• 2 Tracking of Overweight and Obesity from Childhood into Adulthood
• 3 Clinical Correlates of Overweight and Obesity
• 4 Body Composition Assessment in Children and Adolescents – Implications for Obesity
• 5 The Importance of Physical Activity in the Growth and Development of Children
• 6 The Role of Perceived Competence in the Motivation of Obese Children to be Physically Active
• 7 Psychosocial Aspects of Childhood Obesity
• 8 Physical Activity, Appetite Control and Energy Balance
• 9 Eating Behaviour in Children and the Measurement of Food Intake
• 10 Physical Activity Behaviour in Children and the Measurement of Physical Activity
• 11 Environmental Factors and Physical Activity in Children
• 12 Interventions for the Prevention and Management of Childhood Obesity