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Sunday, March 9th 2008

The Obesity War

There seems to be something of a little backlash in the war to prevent obesity. Or maybe the skeptics are just getting more vocal or more coverage.

According to some experts whose views are public health heresy, the jury is still out on how dangerous it is to be fat. “The obesity epidemic has absolutely been exaggerated,” said Dr. Vincent Marks, emeritus professor of clinical biochemistry at the University of Surrey.

Moreover, [obesity skeptics] point to research showing the benefits of a few extra kilos (pounds).

In 2005, Katherine Flegal of the United States’ Centers for Disease Control and Prevention published a study in the Journal of the American Medical Association, finding that overweight people typically live longer than normal-weight people. More than a dozen other studies have come to the same conclusion.

You might remember that 2005 report from the CDC researcher. It made a little bit of splash in the mainstream media as the most prominent study to announce that being overweight (BMI between 25-30) was actually associated with decreased all cause mortality.

In our analysis, we did not find overweight (BMI 25 to <30) to be associated with increased mortality in any of the 3 surveys. Our results are similar to those of a previous analysis of NHANES I and II data that found little effect of overweight on life expectancy.30 Our finding is consistent with other results reported in the literature, although methodologic differences often preclude exact comparisons. In many studies, a plot of the relative risk of mortality against BMI follows a U-shaped curve, with the minimum mortality close to a BMI of 25; mortality increases both as BMI increases above 25 and as BMI decreases below 25,31 which may explain why risks in the overweight category are not much different from those in the normal weight category. Some studies have found that overweight was associated with a slightly increased risk of total mortality compared with the normal weight category.32-34 Other studies have suggested that overweight (BMI 25 to <30) is associated with no excess mortality, particularly in older age groups.35-37,39

But even in Flegal’s study the relative risk of mortality for those who were obese (BMI >30) was clearly higher.

Using relative risks from the combined survey data, we estimated that 111 909 excess deaths in 2000 (95% CI, 53 754 to 170 064) were associated with obesity (BMI ≥30).

Certainly the study had critics concerning its methodology. While there is data (most of it older, such as from NHANES) which has found the same as that 2005 study; but there is a much larger dataset which finds an increased relative risk of mortality both with being overweight and obese.


America Is Fat

Consider Adams’ 2006 look at all cause mortality in the middle aged overweight and obese,

In this large prospective study, obesity was strongly associated with the risk of death in both men and women in all racial and ethnic groups and at all ages. After we accounted for potential bias owing to preexisting disease and residual confounding by smoking status by using midlife BMI values and restricting the analysis to participants who had never smoked, we found that even moderate elevations in BMI conferred an increased risk of death. The risk among participants who were overweight at the age of 50 years was 20 to 40 percent higher than that among participants who had a BMI of 23.5 to 24.9 at that age. The risk among obese subjects was two to at least three times that of participants with a BMI of 23.5 to 24.9. The risk of death among underweight participants was attenuated.

[...]

[W]hether moderate elevations in BMI (i.e., overweight) truly increase the risk of death is controversial.2 Several studies reported no increase in the risk of death among overweight subjects even after those who died during the initial years of follow-up were excluded or subjects were stratified according to smoking status.25,26,27,28,29 Recently, Flegal et al. reported that overweight was not associated with an excess risk of death in the nationally representative samples of U.S. adults drawn from the National Health and Nutrition Examination Survey.29 They speculated that possible causes for their finding might be improved medical management of obesity-related chronic disease or differences between the U.S. general population and populations in other studies.29 Others have suggested that inadequate control for the combined effects of smoking and chronic illnesses could be the explanation.30 Smoking is associated with both a lower BMI and an increased risk of death and can therefore distort the relation between BMI and the risk of death. Statistical adjustment for smoking status does not fully address the problem; the adjusted findings represent a potentially complex combination of the associations between BMI and the risk of death among current smokers, former smokers, and those who have never smoked. Restriction of analyses to persons who have never smoked is a powerful tool for addressing this potential bias. Our cohort included more than 186,000 men and women who had never smoked. When we restricted our analyses to these persons, the relation of obesity to the risk of death was substantially strengthened, and significant increases emerged in the risk of death, even among overweight participants.

While questions may remain, the studies seem to trend that being overweight or obese increases your all cause mortality. But in turn that increased risk of death has drawn criticism over the campaign to document how much obesity is costing western societies.

Notably, Daniel Engber (aka The Slate Explainer) has a recent column entitled, ‘It’s time to shut up about “the cost of obesity”‘.

I’m not going to lie, I have little respect for Engber’s work especially the depth of his explanations when it comes to matters of biological science.


What Are You Talking About??

The Slate column has three main points: 1) the political candidates are overstating the cost of obesity 2) researchers may be overstating the cost of obesity and 3) the alarmism over obesity worsens the problem.

I concede the first point when it comes to Obama and Clinton. Bringing obesity levels down to 1980 levels will not save the government $1 trillion dollars…not in a time frame that anyone currently alive in the United States will see.

But the rest of the column’s angry rant against the perceived alarmism over the obesity epidemic is uh…misplaced.

Engber largely relies on a PLoS published paper out of The Netherlands. In it the researchers conclude that although obese individuals have higher medical costs those costs are for fewer years as the obese have lower life expectancy, and thus the cost of obesity is overestimated.

Here’s how Engber summarizes the study,

It’s true that if you compare two people of the same age and wealth, one slim and the other obese, you can expect the fatter one to have more chronic diseases like diabetes and hypertension. The fatter patient will also make more visits to the doctor, buy more prescription drugs, and otherwise ring up higher medical bills in a given year.

But this analytical approach—used routinely by Finkelstein and other obesity number crunchers—ignores one important fact: Obese people have shorter life spans. Since the elderly are by far the costliest patients, it’s possible that early deaths save taxpayers money in the long run. In fact, fatal diseases almost always return net-cost savings to public health care. Smoking, which causes a host of particularly deadly conditions, turns out to be especially cheap—which is to say, government attempts to curb nicotine addiction have actually cost the United States money. (Niggling mental disorders and musculoskeletal diseases tend to be more expensive.)

In the study however van Baal et al have merely run a highly questionable simulation. The limits in their methodology are…noteworthy. Here’s how the paper describes the methods used,

To estimate annual and lifetime health-care costs conditional on the presence of risk factors, the National Institute for Public Health and the Environment chronic disease model (RIVM-CDM) was used. The RIVM-CDM is a dynamic population model that describes the life course of cohorts in terms of transitions between risk factor classes and changes between disease states over time. Smoking classes distinguished in the model are never-smokers, current smokers, and former smokers. Body weight is modeled in three classes using body mass index (BMI) as an indicator: 18.5 ≤ BMI < 25 (normal weight), 25 ≤ BMI < 30 (overweight), BMI ≥ 30 (obese). The RIVM-CDM has been used in disease projections and cost effectiveness analyses [21–25]. With the model we estimated survivor numbers and disease prevalence numbers for three different hypothetical cohorts consisting of 500 men and 500 women aged 20 y at baseline: (1) an “obese” cohort, never-smoking men and women aged 20 with a BMI above 30; (2) a “healthy-living” cohort, never-smoking men and women aged 20 with normal weight (18.5 ≤ BMI < 25); and (3) a “smoking” cohort, men and women aged 20 with normal weight who had smoked throughout their life. Cohorts were simulated until everybody in the cohort had died.

We have no idea what kind’ve data was put into the RIVM-CDM to run this simulation. And even if we did, this obviously reflects the weakest type of evidence. A simulation? Run until all the simulated cohorts were dead? Is this a joke?

Nevermind the lengthy list of potential problems in extrapolating this study out into the real debate in the American health care system. For example, the simulation fails to acknowledge the rise of obesity in the elderly, as the simulation breaks down it’s cohorts at twenty-years of age as either obese or non-obese without the apparent potential for crossover amongst the groups.

In addition the PLoS paper doesn’t necessarily run parallel with other more legitimate research on teh subject. The issue addressed by the PLoS paper has been addressed circumstantially before with different conclusions.

The point is that the paper Engber cites is an incredibly weak basis on which to vehemently denounce the war on obesity as alarmist. And the Slate column is certainly vehement.

This chew-and-screw narrative feeds on itself. First, it inflates the numbers by ignoring the real effects of an aging population. Then it promotes bias by supplying phony evidence that heavy people are lazy, useless, and a drag on the nation. This in turn makes anyone who thinks he’s a little chubby feel even fatter, which worsens his health and lowers his quality of life. As a result, he spends more money on medical bills and more days at home crying into a bowl of ice cream. And guess what? All of this only increases the cost of obesity!

Look obesity is a major problem which is costing our healthcare system loads. To deny such just denies the large number of studies and the data to the contrary. And while we might be experiencing an alarmism over obesity it is arguable such is a little necessary to make progress in the war on such. The problem is real, but without a little bit of a vaudeville act no one pays attention to it.

And excuse such alarmism if it causes those who have contributed to their own obesity to feel stigmatized, as Engber puts it.

[F]eeling fat…is a major contributor to obesity-related disease and ill health. This would account for the strong association between body-mass index and depression (especially among women), and the high rates of morbidity and mortality that ensue. Sure enough, racial and cultural subgroups with more moderate attitudes toward obesity seem to experience more moderate health effects. Overweight and obese African-Americans, for example, are much less vulnerable to weight-related illness—even among women who are 5 feet 5 inches and 250 pounds.

Sorry, I’ll have to cut this post short, I have to go *roll my eyes*.

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