Creative Destruction

September 11, 2006

On The Most Recent “Fat = Death” Study

Filed under: Fat and fat acceptance — Ampersand @ 5:25 pm

Late last month, a National Cancer Institute study published in the New England Journal of Medicine was given a lot of unskeptical press coverage.

This report, from the AP’s Alicia Chang, is typical in its gloom-and-doom prognosis:

Being a little overweight can kill you, according to new research that leaves little room for denial that a few extra pounds is harmful. Baby boomers who were even just a tad pudgy were more likely to die prematurely than those who were at a healthy weight, U.S. researchers reported Tuesday.

Fortunately for overweight people, the NEJM study is pretty awful, combining bad methodology with dishonest interpretation. The results of this NEJM study, if honestly reported, show that overweight people on average live as long or longer as “normal” weight people; and that the one group of overweight people who did seem to have a significantly elevated risk of mortality, were overweight 50-year-olds who lost weight.

Expect multiple “Alas” posts criticizing this NEJM study. Starting us off is a commentary by Linda Bacon, quoted here with her kind permission.

New Weight Scare Based on Faulty Analysis

by Linda Bacon, PhD, Nutrition Researcher and Professor, NAAFA member

At least 400,000 Americans die of overweight and obesity every year, making it soon to surpass smoking as the leading cause of preventable death [1]. At least that’s what the Centers for Disease Control (CDC) told us.

But an updated federal report, published last year in the Journal of the American Medical Association (and reported in the Late Spring 2005 NAAFA Newsletter), acknowledged that the previous analysis suffered from computational errors [2]. In fact, obesity and overweight only result in an excess of 26,000 annual deaths, far fewer than guns, alcohol or car crashes. And separating overweight from obesity reveals further interesting information: “overweight” people live longer than “normal” weight people.

The data weren’t surprising to those of us who study these issues. This is not an anomaly, but consistent with many other investigations. That it came from the CDC and got published in JAMA were the real astonishing facts.

We waited for the backlash. Fear-mongering about weight is worth billions to industry and is consistent with government policy. Few stand to gain from the news that overweight is benign, if not beneficial. The backlash has been slowly building, and recently came out full force in a highly publicized study published in the August issue of the New England Journal of Medicine [3].

The front page leader in my local paper loudly proclaimed: “Just a few extra pounds is bad for you” and the article title reinforced the message: “Study finds risks for the barely overweight.” Turn to the original report, and you find a consistent conclusion in the abstract: “excess body weight during midlife, including overweight, is associated with an increased risk of death.”

But before you dust off those diet books, let’s take a look at the data itself. The authors worked hard for their conclusion. They examined records from over a half million AARP members that had been surveyed over a ten year period. What they found was entirely consistent with the earlier JAMA report: “overweight” people had the lowest mortality risk. But that wouldn’t serve their purposes. NEJM’s press release wouldn’t look nearly as attractive with that headline.

So they subjected their data to numerous manipulations before finally arriving at a suitable conclusion. First they threw out data on people who were smokers or former smokers. Nope, still shows overweight as benign. They hid this with a sleazy method: using only the top (BMIs of 23 to 24.9) of the “normal weight” group compared to the whole of the “overweight” group.

Then they found an even more creative trick. When they asked participants – some of whom were in their 70s – what they had weighed at the age of 50, they hit paydirt: at last, overweight – at midlife – was associated with increased risk, albeit modest. This will grab the headlines. No need to highlight that we had to whittle our data down to about 5% of the original sample to get this result! (That 40% of the participants chose to leave the question on recalled weight blank should give some indication of the ability of people to accurately report this information.)

Their paper is weak for many other reasons: they had a very low response rate (18%) from a sample that is not nationally representative; their data is based on self-report, which is known to be inaccurate; adjustments for potential confounders were weakly conducted; the list goes on. And they neglected to note another important conclusion: weight loss is associated with a significant increased risk of death for middle-aged “overweight” people.

Come on, New England Journal of Medicine. We expect scholarship, not propaganda.

References

1. Mokdad, A.H., et al., Actual causes of death in the United States, 2000. Journal of the American Medical Association, 2004. 291: p. 1238-45.
2. Flegal, K.M., et al., Excess deaths associated with underweight, overweight, and obesity. Journal of the American Medical Association, 2005. 293(15): p. 1861-7.
3. Adams, K., et al., Overweight, Obesity, and Mortality in a Large Prospective Cohort of Persons 50 to 71 Years Old. New England Journal of Medicine, 2006. 355(8): p. 763-8.

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