The obesity epidemic: Contextual influences on physical activity and body weight

NVITED EDITORIAt The obesity epidemic: Contextual influences on physical activity and body weight Australia, along with the rest of the world, is in the midst of an epidemic of obesity. The prevalence of overweight and obesity h a s escalated dramatically in recent years, having more or less doubled a m o n g adults over the period 1990-2001 (1). There is also evidence of substantial increases in childhood obesity (2). In Australia, almost one in four children and adolescents, one in two women and two in three m e n are overweight or obese (2,a). Given the chronic physical and psychological conditions associated with obesity (4), and its financial impact on the health care system (5), this epidemic poses a formidable threat to population health worldwide. There is no question that obesity is bad for our health. There are, however, a n u m b e r of contentious issues surrounding obesity that are u n d e r debate. These include: the importance of physical inactivity versus dietary factors(6); the a m o u n t of physical activity that is required to prevent weight gain or to bring about weight loss(7); which aspects of diet are important in terms of obesity(s); and whether fitness or fatness is more important for health (9). One issue that h a s received less attention, b u t which is critically important in t e r m s of developing strategies to reverse the epidemic of obesity, relates to the relative importance of individual behaviours versus environmental factors in the epidemic. The recent increase in obesity prevalence is not attributable to genetic factors, since the increase h a s OCCUlTed over too short a period for there to have been substantial changes in population gene pools 11°). In an attempt to understand the causes of the epidemic, m a n y are blaming the environments in which we live, with some commentators describing them as 'toxic'(]1) or 'obesogenic '(12). There is a great deal of rhetoric around the importance of the environment that seems to imply that, if we could simply 'fix' the environment, the obesity problem would be solved. Given the widespread nature of the problem and the potential of 'upstream' interventions to impact on large segments of the population, this view is intuitively appealing. But what evidence is there to support such a proposition? In their review of the changing environment and its role in obesity, Jeffery and Utter (la) concluded: "the scientific evidence available at present is so weak that it seems unlikely that a quick consensus will be reached on...what environmental factors are drMng the epidemic". Evidence on the role of environmental factors in influencing obesity-related behaviours is equivocal. For example, a recent Australian study demonstrated that access to a supportive physical environment was less important t h a n individual-level and social environmental factors in determining adults' physical activity (14). It is noteworthy that despite substantial changes to the environment during the period of the obesity epidemic (la), m a n y people have m a n a g e d to not gain weight (15). It therefore appears that the environm e n t m a y not be the sole driver of the epidemic. Many aspects of the environment have not been investigated but, of those that have, some we might expect to play an important role do not (161. This not surprising since 'the environment' tends to be poorly conceptualised. If we take walking as a n example, is it safety in the local area, the presence of walldng tracks, how well lit these are, access to local facilities, h a ~ n g an aesthetically attractive neighbourhood, or all of these factors, that is important in determining how m u c h an individual walks? We do not possess good conceptual frameworks to help u s decide which environmental exposures are likely to be important. Perhaps as a result, research on 'the environment' tends to be opportunistic. That is, it is often not driven by solid theoretical frameworks, b u t by the available data. We should not lose sight of the fact that "not everything that can be counted counts, and not

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everything that counts can be counted" (Albert Einstein). Much of the available data relate to the physical environment, largely ignoring the socio-cultural environment (eg, how do social connectedness and social capital influence walking?.). Rather t h a n a singular focus on 'the environment' (or for that matter, on any single domain of potential influence), more sophisticated thinking about the contextual influences on obesity is required. Cognitive and social factors are established key determinants of health b e h a w o u r s . We m u s t consider health behaviours in the contexts in which they occur, and examine the interactions between cognitive, behavioural, social and environmental factors, and their relationship to obesity. This will involve drawing on innovative theoretical models to u n d e r s t a n d behaviour, s u c h as social ecological models, which posit a n interaction between individuals and their social and physical environments. In addition, there is a need to embrace new analytical methodologies, including multi-level models that are being developed, to u n d e r s t a n d better the relative importance of the range of potential influences. It is only by gaining an understanding of the contextual influences on physical activity and dietary behaviours that we will obtain the insights necessary to respond effectively to the epidemic of obesity. •

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References 1. Australian Institute of Health and Welfare. A growing problem: trends and patterns in overweight and obesity among adults in Australia, 1980 to 2001. Bulletin No. 8 AIHW Cat. No. AUS 36. Canberra: AIHW; 2003. 2. Magarey AM, Daniels LA, Boulton TJ. Prevalence of overweight and obesity in Australian children and adolescents: reassessment of 1985 and 1995 data against new standard international definitions. Med J Aust 2001; 174:561-4. 3. Cameron AJ, Welborn TA, Zimmet PZ, et al. Overweight and obesity in Australia: the 1999-2000 Australian Diabetes, Obesity and Lifestyle Study (AusDiab}. Med J A u s t 2003;178:427-432. 4. World Health Organization. Obesity, preventing and managing the global epidemic: Report of the WHO consultation on obesity. Geneva: WHO; 1998. 5. Reidpath D, Crawford D, Tilgner L et al. Relationship between Body Mass Index and the use of healthcare services in Australia. Obes Res 2002;10:526-531. 6. Prentice A, J e b b S. Obesity in Britain: Gluttony or sloth? BMJ 1995; 311:437-9. 7. Schoeller DA. But how m u c h physical activity?. Am J Clin Nutr 2003;78 669-670. 8. Gill T. Blinded by science: The National Heart Foundation of Australia's position statement on dietary fat and overweight/obesity. Nutr and Diet 2003;60:151. 9. Blair SN, Brodney S. Effects of physical inactivity and obesity on morbidity and mortality: current evidence and research issues. Med Sci Sports Exerc 1999; 31:$646-62. 10. Hill JO, Peters JC. Environmental contributors to the obesity epidemic. Science 1998; 280:1371-1374. 11. Battle EK, Brownell KD. Confronting a rising tide of eating disorders and obesity: treatment vs. prevention and policy. Addictive Behaviors 1996;21:755-65. 12.Swinburn B, Egger G, Raza F. Dissecting obesogenic envirorLments: the development and application of a framework for identifying and prioritizing environmental interventions for obesity. Prey Med 1999;29:563-570. 13. Gfles-Corti, B, Donovan, RJ. The relative influence of individual, social and physical environment determinants of physical activity. Soc Sci Med 2002;54:1793-1812. 14. Jeffery RW, Utter J. The changing environment and population obesity in the United States. Obes Res 2003;11:12S-22S. 15. Ball K, Brown W, Crawford D. Who does not gain weight? Prevalence and predictors of weight maintenance in young women. Int J Obes 2002;26:1570-1578. 16. Crawford D, Ball K. Behavioural determinants of the obesity epidemic. Asia-Pacific J Clin Nutr 2002; 11: $718-$721. 17. Sallis J, Owen N. Physical Activity and Behavioral Medicine. Thousand Oaks, CA: Sage. 1999.

Kylie Ball and David Crawford C e n t r e for P h y s i c a l Activity a n d N u t r i t i o n R e s e a r c h , Deal(in University, Victoria.

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