Measures designed for prejudice

A fascinating study released this month received absolutely no media notice, perhaps because its myth-shattering findings might be too uncomfortable to acknowledge. It demonstrated one reason why more poor women in developed countries are labeled “obese” than women of privilege.

Israeli researchers, led by Dorit Nitzan Kaluski, M.D., MPH, R.D., at the Ministry of Health and Tel Aviv University, demonstrated that body mass index (BMI) is a discriminatory measure, biased against women who are poor....

In developed countries, obesity is more common among those of lower social and economic status. The researchers wrote that it is popular to blame an “obesogenic” environment with its “unhealthy lifestyles” and to condemn poorer people as eating more cheap, fattening foods and doing less leisure-time exercise. But, as they reported in a study just published in the journal Obesity, a more accurate explanation could partly account for higher rates of obesity among the poor.

Currently, obesity is determined using an arbitrary mathematical formula of weight in kilograms over height (in meters) squared — the body mass index (BMI). For years this measure has been criticized by researchers for lots of reasons, but one is that it is skewed by height, meaning shorter people disproportionately find themselves labeled “obese.”

To investigate the differences in height, weight, socioeconomic status (SES) and the effect on BMI, the researchers examined data from the Israeli National Health and Nutrition Survey, named MABAT. They used the random sample of 2,781 ethnically-diverse Israeli adults who had been visited in their homes by trained public health workers. Similar to the U.S. National Health and Nutrition Examinations Surveys (NHANES), health and diet information had been obtained, and actual measurements had been taken twice by the examiners.

Among women, the prevalence of obesity was about twice as high among those of lower socioeconomic status compared with those of higher status. But, the researchers found:

For any given weight, the socially deprived will have a higher BMI, some of whom will be misclassified as more obese.

In other words, in two women of the same weight the poor one will be more likely to have a higher BMI and fall into the category of being labeled as too fat. Why? The researchers found that adults “of lower SES were significantly shorter than men and women of higher SES.” The differences in height between the higher and the lower SES was 2.3 cm in women, while their weight difference was 4.6 kg. They concluded that the higher prevalence of obesity among poorer women in developed countries is partly due to them being misclassified as obese because of the use of BMI. A 1% change increase in weight leads to a 1% percentage increase in BMI, while a 1% lower height leads to a double percentage increase in BMI, they explained “So, the combined effects are additive.”

After adjusting for age, population group, and ethnic origin, height was significantly inversely associated with obesity among women, with a 7% increase in risk of obesity for each 2.5-cm decrease in height.

This has significance especially when looking at population-wide statistics and making conclusions about obesity or “bad” behaviors, when the real issue is the social and economic situation. Height is a complex trait controlled by both genetic and environmental factors, they explained. The body of research, they said, points to decreased height as reflecting “suboptimal nutrition during fetal, child, and adolescent life, notwithstanding the influence of heredity.” Thus, they wrote, the higher rates of obesity seen among poor people could be due to inadequate prenatal and childhood nutrition, “rather than to various degrees of ‘sloth or gluttony.’”

According to Dr. Kaluski’s research, food insecurity and not having enough to eat, as found amongst poorer populations, leads to higher weights:

[I]t was previously shown that women exposed to starvation conditions at childhood presented with increased plasma levels of insulin-like growth factor and weakly decreased levels of its plasma carriers at adulthood. These results are opposite to the immediate responses seen under starvation and suggest a compensating hormonal overshoot after improvement of famine condition. Possibly, inadequate childhood nutrition may also result in an overshoot of certain hormones and, subsequently, compensatory higher weight at adulthood.

This speaks to the need to address poverty and ensure women and children have enough calories and higher-density and nutritious foods to eat. It also points out that promoting dieting is illogical and will only raise weights long term. Which, in fact, every study on dieting has shown this to be the case, tripling the development of obesity among children who’ve restricted their eating and tried to diet for weight control.

They noted that obesity, in turn, affects SES, with discrimination against obese people well-documented as "impeding attempts to attain higher status."

These researchers went on to demonstrate how simply making minor changes to the mathematical formula for BMI could dramatically change who is labeled “overweight” and “obese,” even virtually eliminating the SES disparities. When they recalculated the BMIs among the 1,410 women in their study using weight/height^1/2 they reduced the prevalence of obesity among women of lower SES and significantly reduced the association between poor women and “obesity:”

In short women of lower SES, the prevalence of obesity was reduced by 7-fold when calculated by weight/height^1/2 index rather than by BMI. However, for short women of middle and high SES, the prevalence of obesity was reduced by only 4.5-fold when calculated by weight/height^1/2 index compared with BMI.

Why does a discriminatory arbitrary measure with such obvious problems — that leads to the greater condemnation of those of certain ethnic and genetic backgrounds, those who are aging and those who are poor — continue to be favored? The answer lies in the fact that the war on obesity isn’t an issue of health, any more than dieting is about health — how can it be when fat people have a survival advantage, while chronic diseases of aging are shared by people of all sizes, and there is no evidence that losing weight prolongs life?

No, the war on obesity is about aesthetics and classism and ageism. It is a war against people some don’t want to see.

© 2007 Sandy Szwarc