Fat 'fact' takes on life of its own
Paul Campos, Rocky Mt. News
http://www.rockymountainnews.com/drmn/news_columnists/article/0,1299,DRMN_86_1213969,00.htmlJune 18, 2002
An abiding weakness of the conventional wisdom is that, once a supposed fact has become part of that wisdom, it becomes almost impossible to dislodge it. Contemporary journalism contributes to this problem by relying on technologies that help ensure an assertion, once it is repeated enough times, will never be checked against the actual evidence. Consider for example the claim that fat kills 300,000 Americans per year, and is thus the nation's second-leading cause of premature death, trailing only cigarettes.
A Lexis database search reveals that this "fact" has been repeated in more than 1,000 news stories over the past three years alone. Yet the evidence for this claim is so slim as to be practically nonexistent.
As University of Virginia professor Glen Gaesser points out in the forthcoming revised edition of his book
Big Fat Lies, the supposed source for this claim was a 1993 medical study that made no such assertion. That study attributed around 300,000 extra deaths per year to sedentary lifestyle and poor dietary habits, not to weight, which was not even evaluated as a risk factor. Indeed the authors of the study, Michael McGinnis and William Foege, became so frustrated by the chronic miscitation of their data that in 1998 they published a letter in the New England Journal of Medicine, objecting to the misuse of their study.
A year later the journal published an article which actually did assert that obesity causes approximately 300,000 deaths annually. This article, "Annual Deaths Attributable to Obesity in the United States," is a classic example of junk science at its worst. After calculating the death risk associated with various weight levels derived from six epidemiological studies, the authors employed the following assumption: "Our calculations assume that all excess mortality in obese people is due to their obesity" (emphasis added). That was, to put it mildly, a remarkable assumption. As Gaesser points out, "the authors made no attempt to determine whether other factors -- such as physical inactivity, low fitness levels, poor diet, risky weight loss practices, and less-than-adequate access to health care, just to name a few -- could have explained some, or all, of the excess mortality in fat people."
In fact there is a great deal of evidence that such factors are far more relevant to mortality than weight. Indeed, long-term studies conducted at Dallas' Cooper Institute, involving tens of thousands of subjects tracked for a decade or more, have concluded that
all of the excess mortality associated with increasing weight is accounted for by activity levels, not weight. These studies show moderately active fat people have far lower mortality rates than thin sedentary people, and essentially the same mortality rates as thin active people. In other words, adding just one variable to the mix -- activity levels -- eliminates fat as a risk factor (the activity levels associated with optimum mortality rates are quite modest -- a brisk daily half-hour walk will by itself put a person in these categories).
Furthermore the 300,000-deaths-per-year figure was derived without taking into account factors such as yo-yo dieting and diet drug use, both of which have been shown to have devastating effects on health. Nor were variables such as class -- poor people die sooner than the well-off -- and social discrimination, which has been shown to have a very negative impact on health, taken into account. In short, the claim that fat causes 300,000 deaths per year should be dismissed as an assertion for which there is essentially no evidence. Journalists in particular ought to start noticing that fact, rather than endlessly reprinting the same piece of junk science.
Paul Campos is a professor of law at the University of Colorado. He can be contacted at paul.campos@colorado.edu.
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