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An Epidemic of Obesity Myths
A Shared Problem

"Our estimates may be biased toward higher numbers due to confounding by unknown variables." —David Allison in JAMA, 1999
Both Allison’s and Flegal’s studies presume that any increased rate of death in overweight or obese people is the result of their excess weight—a very unlikely assumption. Those without a high school diploma are nearly twice as likely to be obese as those with a four-year degree.

They are also much less likely to have health insurance and to receive quality health care. Other factors that could increase the risk of death among obese people include sedentary lifestyles, genetic ailments, and the negative effects of diet pills—including amphetamines, the weight loss drug of choice for much of the last half-century. A generation ago, 8 percent of all U.S. prescriptions were for weight-loss amphetamines. Allison and his co-authors acknowledge that their calculations assume "all excess mortality in obese people is due to obesity," and that this assumption had the effect of overestimating the total number of obesity-related deaths. They continue: "Our estimates may be biased toward higher numbers due to confounding by unknown variables."

Echoing that point, Flegal’s team writes, "other factors associated with body weight, such as physical activity, body composition, visceral adiposity, physical fitness, or dietary intake, might be responsible for some or all of the apparent associations of weight with mortality."

Dr. David Williamson, who co-authored the study with Flegal, explained: "…we cannot truly say there is a causal relationship [between obesity and mortality]." The New England Journal of Medicine (NEJM) pointed out in a 1998 editorial that "mortality among obese people may be misleadingly high because overweight people are more likely to be sedentary and of low socio-economic status." In a letter amplifying their original editorial, the NEJM editors further note:

"Calculations of attributable risk are fraught with problems. They provide only an upper bound for the effect of a single variable, because many other factors, both recognized and unrecognized, may also be contributing to the outcome. When several known factors are taken into account, it is even possible to find that they account for more than 100 percent of deaths—a nonsensical result."
Even the CDC has noted the inherent problems in measuring the risk attributed to poor diet and physical activity. In a paper on physical activity, the agency writes:
"[Mortality estimates] are generally derived by calculating the population attributable risk (PAR) … Such estimates are inherently uncertain because they do not take into account the reality that some people have more than one risk factor for a disease; for these people, the elimination of a single risk factor (e.g., by becoming physically active) may not reduce mortality risk to the level attainable for people who initially have only that one risk factor. PAR methods thus overestimate the proportion of deaths avoidable by eliminating one modifiable risk factor, in this case physical inactivity."
The CDC’s internal review committee’s report notes: "Double counting [of deaths] is mentioned clearly in the Discussion section but not in the Introduction and not clearly in the Methods."

Dr. Jon Robison of Michigan State University explains the dubious logic behind the 400,000 number:
"Perhaps the most glaring absurdity about the 400,000 deaths due to obesity study resides in the pronouncement that ´┐Żall excess mortality in obese people is due to their obesity.’ This is as preposterous as claiming that differences in mortality rates between blacks and whites are solely a result of the color of their skin!"
University of Virginia Professor of Exercise Physiology Glenn Gaesser reinforces the point:
"The authors made no attempt to determine whether other factors, such as physical inactivity, low fitness levels, poor diet, risky weight loss practices, weight fluctuation, use of weight loss drugs, less than adequate access to health care, etc. could have explained some or all of the excess mortality in large people."