Last week we told you about a bombshell article in Scientific American critiquing a study that found obesity is set to substantially shorten Americans’ life expectancy. Senior science reporter W. Wayt Gibbs writes that when pressed, the study’s co-author, Dr. D.B. Allison, admits: "These are just back-of-the envelope, plausible scenarios. " That’s quite an admission for Allison, who is alsothe father of the faulty formula used by the Centers for Disease Control and Prevention (CDC) to estimate 400,000 obesity-related deaths per year. Providing yet more vindication for our earlier critiques, Gibbs notes that these "estimates were compromised by dubious assumptions, statistical errors and outdated measures."Noting that Allison has received money from scores of companies and organizations that benefit from hyping fears of flab, Gibbs reports:

Media coverage of the obesity epidemic surged in 1999 following a report in the Journal of the American Medical Association by [Dr.] 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 reflect 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 …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 as stemming from "poor diet and inactivity." The new figure corrected only data-entry mistakes, however…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.