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Monday, June 25, 2012

Obesity and social disadvantage

Frequently, when chatting with my middle class friends on nutrition and health, I have to argue long and hard against some preconceived notion of the truth behind the topic of discussion. Of all of these issues, the one I encounter most frequently and the one that meets most resistance to change is the view that the problem of obesity is really a problem of the lower socio-economic groups.  A frequent argument put forward is that  “if you look at their shopping trolleys in supermarkets, they are laden with all sorts of junk foods”.  So let me give you the facts. Taking the Irish population as a whole and using the IUNA database, body mass index (BMI kg/m2) is 26.8 among the professional workers, 27.4 among non-manual workers, 28.4 among skilled workers and 26.0 among the unskilled workforce. An acceptable level of BMI is 25 and I should add that the variance (standard deviations) of these figures is broadly similar. Now you can look at this and say: ”See I told you so. There is a graded rise in BMI from professional to skilled workers” and this goes nicely with the social class stereotype. The socio-economically disadvantaged are seen as lacking money to buy healthy food, and so poorly health aware as to not know good food choices from bad food choices and, in some cases, they are deemed to lack the literary skills to read labels correctly. This leads the debate on public health nutrition to shift into policy decisions in which actions toward social issues begin to dominate. In case you think that this Irish data is unique, please consult the Report of the Health and Social Care Information Centre’s report: Statistics on obesity, physical activity and diet: England, 2011.  To directly quote the report: “Table 7.3 on page 128 of the HSE 2009 report shows that there are very little differences in mean BMI by equivalised household income for men with the exception of those in the lowest income quintile who had slightly lower BMI; in contrast for women, those in the lower income quintiles had a higher mean BMI than women in the highest quintile. Among women, the proportions who were obese were higher in the lowest three income quintiles (ranging from 27%-33%) than women in the highest two quintiles (ranging from 17%-21%). The relationships between BMI and income for men were less clear”. Canadian data is quite similar but US data[1] does show quite a different pattern with obesity rising more rapidly among the socially disadvantaged. However, these data when carefully examined reveal some intriguing facts.  Among white men and women, the rate of rise in the % obese has grown equally across socio-economic status (SES) over the 30 years from 1970 to 2000. The lowest SES in 2000 had an obesity rate of 28.3% in men compared with 23.9% among those in the highest SES. For women, the figures were 36.3% and 26.6% respectively. However, when we look at black males, the % obese jumped from 4% to 33% in that 30-year period among the highest SES. The middle and lowest SES groups started off with a figure of 15%, which grew to 24%. For black women, the total reverse was seen. How does on e begin to make sense of that?

I should add that if you look at dietary patterns across socio-economic status in the Irish IUNA data, you see no biologically meaningful change in the % energy from fat or sugar and this is borne out by data from the Household Budget Survey which tracks expenditure on foods. That data shows no difference in food purchasing patterns across socio-economic status.

There is a bottom line here and that is that obesity is everywhere. To argue over one unit of BMI between the haves and the have-nots is to quite simply miss the point. Statisticians can construct models, which show that controlling for age, gender, smoking and so on, the relative risk of obesity rises with lower socio-economic status. They are welcome to that but if it begins to drive public health nutrition policies toward some social solutions, then they are being unhelpful. Of course, social disadvantage needs to be a factor we consider in all aspects of public health. But what is driving the increased adiposity of judges, teachers, doctors and so forth. It is not a lack of knowledge, not due to literacy or lack of income. The do-gooders of public health nutrition need to read the real population statistics and make appropriate recommendations.

[1] The Obesity Epidemic in the United States—Gender, Age, Socioeconomic, Racial/Ethnic, and Geographic Characteristics: A Systematic Review and Meta-Regression Analysis Youfa Wang and May A. Beydoun Epidemiologic Rev 2007;29:6–28

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