Just in time for New Year’s resolution season, The Journal of the American Medical Association comes out with a study casting doubt on the medical dogma that even a small bit of “extra” weight will kill you.
The study in question is an analysis that used some 100 previous studies on death and body mass index – an index based on weight and height. CDC researcher Katherine Flegal concluded that people who fell into the World Health Organization’s “overweight” category were 6% less likely to die than people in the “normal” range. Obese people were more likely to die.
The study deserved attention. It addresses a major heath issue, since more than 30 percent of Americans qualify for the so-called overweight category – the middle range between what the medical community deems healthy and obese. Flegal was widely quoted saying the take-home message should be that the relationship between weight and health is more complicated than previously assumed, though most news outlets focused on the apparent longevity edge of those people WHO deemed overweight. Headlines declared that extra fat would help you live longer, or extra pounds would cut risk of early death, though the stories didn’t support such a sweeping conclusion. Perhaps we need to rethink what we call "extra" pounds.
I was surprised at the similarities between all the news stories I read. Nearly all took the standard dueling experts format with Harvard School of Public Health researcher Walter Willet playing the skeptic’s role. Some of the stories did a better job than others in letting Willet explain why he thought this latest study was “rubbish” as he put it.
I was still left wondering what the scientific basis had been for our current dividing lines between normal, overweight and obese. How did the medical community decide who was “overweight” before? Surely it must have been based on some science. What was the evidence in favor of the old standard and why did this new meta analysis suggest something so different? Does this new analysis really show that “overweight” is good, or merely that we haven’t yet figured out how to define normal and overweight?
The New York Times story by Pam Belluck did note that our criteria for normal and overweight may need revising:
Experts also said the data suggested that the definition of “normal” B.M.I., 18.5 to 24.9, should be revised, excluding its lowest weights, which might be too thin.
In the NPR shots blog, Allison Aubrey gave Willet an opportunity to discuss cause and effect and the possibility that some of the thin people in this new analysis were thin because they had been sick, not sick because they were thin.
Nanci Helmich at USA Today did quote Willet making general references to existing studies showing dangers of being overweight but not obese. The same story, which used the misleading term “obesity paradox” in the headline, quoted Steven Heymsfield, one of the authors on an accompanying editorial, saying this: "We don't really know the ideal weight for a long life and optimal health. Science is still working that out. But falling in the normal, healthy weight range is still the safest place to be."
If we don’t know, why should it be safer to be in the normal healthy range? If you’re a big, strapping, muscular person, does that mean you need to go on a diet? Is there some standing body of evidence on which we’ve defined the healthy range? And if so, why would he say we don’t know? Lots of questions were left unanswered and the dueling experts were not challenged nearly enough.
Those on both sides of this debate were quoted pointing out that the link between BMI and health is complicated. Many stories also noted that BMI doesn’t distinguish between fat and muscle, so body builders and athletes can be classified as overweight when they’re far from fat. I recall, from the early days of BMI, some commentators pointing out that Arnold Schwarzenegger would qualify as overweight if not obese. I can’t quite picture doctors telling the Terminator he’s too fat.
Other stories noted studies that show big biceps are fine, big butts won’t shorten your life, but stomach fat could be a harbinger of illness. Weight is turning out to be like real estate – location location location.
Reuters: More Evidence for Obesity Paradox