Socio-economic factors in obesity: a case of slim chance in a fat world

The global obesity pandemic has been well-documented and widely discussed by the public, the media, health officials, the food industry and academic researchers. While the problem is widely recognised, the potential solutions are far less clear. There is only limited evidence to guide decisions as to how best to manage obesity in individuals and in populations. While widely viewed as a clinical and public health problem in developed countries, it is now clear that many developing countries also have to grapple with this problem or face the crippling healthcare costs resulting from obesity-related morbidity. There is also abundant evidence that obesity is socio-economically distributed. In developed countries persons of lower socio-economic position are more likely to be affected, while in developing countries, it is often those of higher socio-economic position who are overweight or obese. The aim of this paper is to briefly review the evidence that links socio-economic position and obesity, to discuss what is known about underlying mechanisms, and to consider the role of social, physical, policy and cultural environments in explaining the relationships between socio-economic position and obesity. We introduce the concept of 'resilience' as a potential theoretical construct to guide research efforts aimed at understanding how some socio-economically disadvantaged individuals manage to avoid obesity. We conclude by considering an agenda to guide future research and programs focused on understanding and reducing obesity among those of low socio-economic position. Key Words: socio-economic factors, obesity, environment, social environment, resilience. Introduction Population obesity as a socio-economically patterned phenomenon There is a substantial body of evidence that demonstrates that obesity is associated with socio-economic position (SEP). That literature was first reviewed by Sobal and Stunkard in 1989. 1 In their now classic paper, they examined 144 mostly cross-sectional studies and concluded that, in developed countries, SEP was consistently inversely associated with obesity among women. Among men and children, however, the associations between SEP and obesity were less consistent. For example, of 66 studies including data from men, 52% found an inverse relationship between SEP and obesity, but 30% found the opposite -a direct relationship -and 17% found no association. In developing societies, Sobal and Stunkard's 1 review showed that SEP was strongly directly associated with obesity among men, women and children. In a more recent review, Ball and Crawford 2 examined the evidence regarding the associations between SEP and weight change. That review identified 34 papers published between 1980 and 2002 that reported on longitudinal studies conducted in developed countries. Based on the more rigorous of these studies, the authors concluded that occupation was inversely associated with weight gain. For example, in a sample of almost 8,000 adults participating in the Whitehall study, participants in the lowest occupational category (clerical) had 1.64 (men) or 2.16 (women) times the odds of long-term major BMI increases (>3 BMI points) compared with those in the highest occupational category (administrators). 3 The review also showed that the association between education and weight gain was less consistent, and that income was inconsistently associated with weight gain. While some previous evidence suggested that obesity may actually be an antecedent to low SEP, 4,5 results of Ball and Crawford's 2 review of longitudinal studies suggests that SEP precedes weight gain and risk for obesity, rather than the reverse. Too few studies from developing countries were identified to be included in that review, and similarly the remainder of the present paper focuses on developed countries, from where the majority of research evidence is derived. Socio-economic position and nutrition and physical activity behaviours There seems little doubt that the epidemic of obesity that we are witnessing worldwide is attributable to excess energy consumption and inadequate energy expenditure. In order words, at a population level, changes in both eating patterns and in physical activity habits are important in terms of obesity aetiology. 7-11 While the search for specific behavioural drivers of obesity continues, it is likely that these comprise both eating and physical activity-related behaviours. There is good evidence that the socio-economic distribution of eating patterns and of leisure-time physical activity are consistent with those found for obesity. Studies show that persons from low socio-economic backgrounds are less likely than those from high socio-economic backgrounds to participate in organised sport and leisure-time physical activity