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The June issue of Scientific American had an amazing article. Apparently obesity is not a cause of mortality.

And yet an increasing number of scholars have begun accusing obesity experts, public health officials and the media of exaggerating the health effects of the epidemic of overweight and obesity.

The article contains a lot of data and information and I recommend reading it strongly. Note, the magazine is only available by subscription, but this one article is worth the price of admission. I'll quote on breakout box here just to give you an idea.

Media coverage of the obesity epidemic surged in 1999 following a report in the Journal of the American Medical Association by David B. Allison and others that laid about 300,000 annual deaths in the U.S. at the doorstep of obesity. The figure quickly acquired the status of fact in both the popular press and the scientific literature, despite extensive discussion in the paper of many uncertainties and potential biases in the approach that the authors used.

Like election polls, these estimates involve huge extrapolations from relatively small numbers of actual measurements. If the measurements?in this case of height, weight and death rates?are not accurate or are not representative of the population at large, then the estimate can be far off the mark. Allison drew statistics on the riskiness of high weights from six different studies. Three were based on self-reported heights and weights, which can make the overweight category look riskier than it really is (because heavy people tend to lie about their weight). Only one of the surveys was designed to refl ect the actual composition of the U.S. population. But that survey, called NHANES I, was performed in the early 1970s, when heart disease was much more lethal than it is today. NHANES I also did not account as well for participants? smoking habits as later surveys did.

That matters because smoking has such a strong infl uence on mortality that any problem in subtracting its effects could distort the true mortal risks of obesity. Allison and his colleagues also used an incorrect formula to adjust for confounding variables, according to statisticians at the CDC and the National Cancer Institute.

Perhaps the most important limitation noted in the 1999 paper was its failure to allow the mortality risk associated with a high BMI to vary?in particular, to drop?as people get older.

Surprisingly, none of these problems was either mentioned or corrected in a March 2004 paper by CDC scientists, including the agency?s director, that arrived at a higher estimate of 400,000 deaths using Allison?s method, incorrect formula and all. Vocal criticism led to an internal investigation at the CDC; in January the authors published a ?corrected? estimate of 365,000 obesity-related deaths a year, which they labeled asstemming from ?poor diet and inactivity.? The new figure corrected only data-entry mistakes, however.

Meanwhile another CDC scientist, Katherine M. Flegal, was preparing to publish a new and much improved estimate based entirely on nationally representative surveys that actually measured weights and heights. Flegal?s analysis allows for risks that vary with age and claims to correct properly for confounding factors. But ?the biggest reason that we get different results is that we used newer data,? she asserts.

As illustrated in the chart below, the new analysis suggests that it is still far from certain whether there is any measurable mortality toll at all among overweight and obese Americans as a group. Even among the moderately and severely obese (those whose BMI exceeds 35), the plausible annual mortality found in the 1988?1994 survey ranges from 122,000 extra to 7,000 fewer deaths than one would expect based on the death rates of ?healthy weight? people.

There it is, the best we can really say is that we do not know about the effects of weight on mortality. Next time somebody tells you you need to lose 15 pounds or your going to die young, shove this article at them.