It is virtually official U.S. government policy that obesity kills 300,000 people every year. But a new analysis by some brave federal researchers exposes this factoid for what it really is — junk science.
Secretary of Health and Human Services Tommy Thompson said last March, “Americans need to understand that overweight and obesity are literally killing us.”
Thompson made that remark on the occasion of the release of a study by the Centers for Disease Control and Prevention estimating that poor diet and lack of physical activity caused 400,000 deaths in 2000 — up from 300,000 in 1990 and on par with the supposed 435,000 annual deaths attributed to smoking. That is just where the new analysis picks up.
“It is frequently stated in scientific and lay literature that obesity causes 300,000 deaths per year in the U.S. It has been suggested that obesity is second only to smoking as a preventable cause of death,” write researchers from the National Center for Health Statistics (search) in the September issue of the American Journal of Public Health.
But “many methodological and conceptual difficulties arise in attempting to estimate the number of deaths in the United States that are attributable to obesity (search)," say the NCHS researchers. The basic flaw, they say, is that the alleged 300,000 deaths are generated by statistics, not science.
“The concept of a death being ‘attributable’ to obesity generally relies on a statistical excess of deaths among people who are obese, relative to people who are nonobese, rather than on identifying obesity as the specific cause of death for an individual,” they write.
“Obesity itself may not be the only contributing factor to this statistical excess, but rather a marker for other factors such as sedentary behavior or adverse body fat distribution.”
In other words, just because someone is obese and they die, it doesn’t necessarily follow that their obesity was the cause. The NCHS researchers point out that the populations analyzed to derive obesity deaths are biased because they intentionally exclude elderly persons or other persons who are at the highest risk of death and most likely to die of factors unrelated to obesity.
“Such exclusions result in estimates of the relative risk associated with obesity that apply only to a subgroup of the population and cannot necessarily be extrapolated to deaths in the entire population,” write the NCHS researchers.
Though I’ve written about many of these issues before, the NCHS researchers did have a surprise in store for me. Studies have generally reported that the risk of death associated with obesity actually declines with increasing age. A 1998 review of seven studies on bodyweight and mortality in elderly persons reported that only two of those studies reported a statistical correlation between bodyweight and premature death — and of those two studies, one study reported no association for those aged 75 years or over. The other five studies either found no correlation or a strong negative correlation.
Researchers are not sure why, but it has been suggested that in old age, the protective effects of obesity might counterbalance some negative effects.
“The protective effects of obesity include greater nutritional reserves in times of stress, lower rates of injury from falls and lower rates of osteoporosis,” speculate the NCHS researchers.
Since 75 percent of the 2 million annual deaths in the U.S. occur among those 65 years and older, the potential protective impact of obesity in old age may reduce the obesity body count significantly — subtracting as much as 200,000 from the oft-touted 300,000 figure, according to the NCHS researchers.
The NCHS researchers conclude by saying: “We have identified important limitations in the data that are currently available to estimate the number of deaths in the United States that are attributable to obesity. Our examination suggests that given present knowledge about the epidemiology of obesity (search), it may be difficult to develop accurate and precise estimates.
“We urge caution [Secretary Thompson, are you reading this?] in the use of current estimates of the number of deaths attributable to obesity and urge researchers to devote greater efforts to improve the data and methods used to estimate this important public health issue.”
Though I applaud the NCHS researchers for daring to challenge public health orthodoxy — never an easy thing to do for government researchers — I must quibble with their misclassification of obesity as a “public health issue.”
Obesity is not an infectious disease and so is not a traditional public health issue. This fact, however, hasn’t stopped the public health establishment from hyping obesity in order to boost the bureaucracy’s ever-shrinking role in the lives of increasingly long-lived Americans, who suffer less than ever from infectious diseases and other traditional public health maladies.
Fortunately, this new analysis makes progress toward removing about two-thirds of the 300,000 reasons for misclassifying obesity as a "public health" issue.
Steven Milloy is the publisher of JunkScience.com, an adjunct scholar at the Cato Institute and the author of "Junk Science Judo: Self-Defense Against Health Scares and Scams" (Cato Institute, 2001).