TCS Daily


Only the Plump Die Young?

By John Luik - April 29, 2005 12:00 AM

Some people don't know when to quit. You would think that after the debacle over the grossly inflated estimates of so-called obesity-related deaths from the US Center for Disease Control that the fat police would have the decency to just shut up. But the scary junk science stories about killer fat just keep coming. The latest is an alarmist study in the New England Journal of Medicine titled "Children's Life Expectancy Being Cut Short by Obesity."

The study, by a team led by Jay Olshansky of the University of Illinois, makes the astonishing and quite unsupported claim that for the first time since at least 1900 children born in the United States today will live shorter lives than their parents due to obesity-caused mortality. The study's only problems are:

        1)     It flies in the face of the standards of contemporary 
                evidence-based medical research since the "study" is not based 
                on any scientific evidence but simply on a "collective judgment" 
                about disease and mortality trends.

        2)     It is contradicted by a mass of real scientific evidence from the 
               last fifty years about the relationship between obesity and death.

To begin with, it is hard to describe the Olshansky study as science at all since there is no empirical evidence, other than "trends" cited in support of the author's claims. As the authors note, "from our analysis of the effect of obesity on longevity, we conclude that the steady rise in life expectancy during the past two centuries may soon come to an end." According to Olshansky and his co-researchers, Americans would live longer if everyone "who is currently obese were to lose enough weight to obtain an 'optimal' BMI, which we defined as a BMI of 24."

The problem with this claim is that it is contradicted by a significant number of empirical studies of the connection between weight and premature mortality, including one by David Allison, one of Olshansky's co-authors. According to Allison's 1999 study in JAMA "Annual Deaths Attributable to Obesity in the United States", which claims that obesity causes about 300,000 premature deaths a year, individuals with BMI's of 20 ("normal") have the same risk of early death as those with BMI's of 30 ("obese"). Both of these groups have higher risks of dying than those who are overweight with a BMI of 25. Again, the 1995 Nurses Study found that those nurses with BMI's of 19-24.0 had almost identical mortality rates as nurses with BMI's of 25-31.9. So how can an "ideal" BMI of 24 possibly lead to living longer?

Second, the US National Center for Health Statistics, in its most recent US Life Tables (2000), reports that overall life expectancy at birth was 76.9 compared with 47 in 1900. Overall life expectancy increased by more than six years from 1970 to 2000, despite the claim that for the last ten years there has been an unprecedented obesity epidemic in which weights have increased by up to 75%.

Again, the author's worry about the connection of childhood obesity with such diseases as Type 2 diabetes is not supported by the scientific evidence. With the change in the definition of diabetes (from fasting blood sugar of 140-126) millions of new diabetics were minted overnight, just as millions of new overweight and obese were created with the "revised" BMI categories.

But even with this change there is little evidence of a substantial increase in blood sugar levels across the population. Despite the claims of an obesity-fueled diabetes epidemic, CDC figures show that during the 1990's the disease increased only from 8.2 to 8.6%, a statistically nonsignificant increase. Finally, a number of recent studies have shown that dieters have a higher risk of the disease than others. Studies have also reported that the most effective strategy for avoiding Type 2 diabetes is not through weight loss by through changes in physical activity and diet.

But what really contradicts the claim that today's children will live shorter lives than their parents due to obesity is the ever-growing number of serious scientific studies that over the last 50 years that have looked at the link between obesity and premature death. These studies refute Olshansky's claim of a reduction in mortality if everyone who is currently obese were to reduce to a BMI of 24.

Starting in 1950's in the midst of another alleged obesity epidemic that had the medical community declaring obesity to be the number one threat to the nation's health, there has been a steady stream of studies that have shown that being overweight is not a cause of increased mortality. The Framingham study of some 5,000 people over 30 years found, for instance, that the worst life expectancies were for the thinnest men. According to Reubin Andres of the US National Institute on Aging, none of the scientific studies on weight and mortality supports the claim that excessive weights lead to increased mortality. As he noted "The major studies of obesity and mortality fail to show that overall obesity leads to greater risk." This conclusion is echoed in the Seven Country Study by Ancel Keys. In a recent re-examination of Keys data, researchers found that being overweight -- a BMI of 25-30 -- had no effect on mortality and even the obese still had lower death rates than thin men.

Another longitudinal study involving almost two million Norwegians followed for ten years found those with BMI's from 26-28 ("overweight") had the highest life expectancy. As the journal Obesity Research noted in 2002, "Compared with normal weight, overweight and obesity did not significantly increase all-cause mortality risk."

All of this suggests that the Journal's latest study is more likely the stuff of science fiction rather than science. Despite the alarmist cries of declining life expectancies, the scientific evidence of the last half century does not support the claim that obesity will mean shorter lives for our children. As the Journal put it so well in 1998, "The data linking overweight and death, as well as the data showing the beneficial effects of weight loss, are limited, fragmentary and often ambiguous. Most of the evidence is either indirect or derived from observational epidemiologic studies, many of which have serious methodologic flaws." Indeed. Perhaps the Journal's editors could paste that comment up somewhere in their office so that it might be consulted every time another "scientific" obesity study arrived.

John Luik is a health policy analyst currently writing a book about obesity in America.

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