Health

No, Being Fat Won't Help You Live Longer

A decade or more of "obesity paradox" research is just plain wrong.

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West Coast Surfer/picture alliance / moodboard/Newscom

File another one under "health research too good to be true." After more than a decade of reports that extra weight could boost longevity and protect against death by heart disease, a new study casts doubt on this "obesity paradox."

The purported paradox first appeared in research on people diagnosed with heart disease. After a diagnosis, overweight and mildly obese individuals lived longer than their normal-weight counterparts, according to research funded by the federal government. In the hands of the health press, this became 1,000 headlines about how being overweight was actually good for your health.

Yet according to Northwestern University's Sadiya Khan, the real reason the data appeared to show this weighty benefit is that overweight patients were developing heart disease earlier in life than their normal-weight peers. Yes, they tended to live longer following a heart disease diagnosis—but that's only because they were getting heart disease years earlier than skinnier people did.

As the Pittsburgh Post-Gazette puts it, "one of the main effects of carrying around too much excess weight is that you get fewer years of disease-free life."

While the mildly overweight live about as long as their normal-weight peers, heavier folks spend more of those years in ill health. And extra weight is also associated with a greater risk of developing cardiovascular conditions in the first place, says the Khan study.

According to Khan's findings, published Wednesday in JAMA Cardiology:

  • 32 percent of men with a body mass index (BMI) in the normal range (between 18.5 and 24.9) suffered a heart attack, stroke, or congestive heart failure during their time in the study, compared to 37 percent of overweight men (defined as those with a BMI between 25 and 29.9), 47 percent of obese men (BMI between 30 and 39.9), and 65.4 percent of morbidly obese men (BMI 40 or above).
  • 21.5 percent of women with a normal BMI had a heart attack, stroke, or heart failure, compared to 27.9 percent of overweight women, 38.8 percent of obese women, and 47.6 percent of morbidly obese women

Khan's research relies on data from the Cardiovascular Disease Lifetime Risk Pooling Project, and it includes an analysis of medical information on 190,672 Americans, each of whom were followed for at least 10 years.

Overall, extra weight raised a middle-aged man's lifetime risk of heart problems by somewhere between 18 percent (for the overweight) and 98 percent (for the morbidly obese), relative to their normal-weight counterparts. For middle-aged women, being overweight meant a 42 percent higher chance of heart problems, while being obese raised the risk by 75 percent and being morbidly obese raised the risk by 80 percent.

All this prompts the question: How did previous researchers on this topic manage to get things so wrong?

One answer is that early studies on the topic usually looked only at the period of time following a heart-disease diagnosis or negative heart-related event rather than considering a longer time period. And while researchers themselves often weighed the impact of this limitation—as well as the limitations of using measures such as BMI as a biomarker in the first place, and the danger of putting too much stock in one particular health outcome, like developing heart disease, while ignoring others—the nuances rarely survived a study's translation to a mass audience. Hence headlines like "A few extra pounds may cut risk of early death," "Why being overweight means you live longer," and "Scientists now think that being overweight can protect your health."

But bad health reporting doesn't deserve all the blame. Plenty of the published studies on the "obesity paradox" simply weren't that good, reflecting a larger crisis of credibility in the scientific and academic publishing community—a credibility crisis that's all too often overlooked in our government's rush to push food regulations under the veneer of science. Recently, this led to nationally implemented school "smarter lunchroom" programs that were informed by a body of research found to have serious flaws. Indeed, some of the research may have been entirely fabricated.

The "obesity paradox" is also rooted in the government. It starts with the National Institutes of Health (NIH). In 2005, an NIH researcher named Katherine Flegal published an analysis of Centers for Disease Control and Prevention data on mortality and weight, following this up over the next decade with several more papers in a similar vein.

"A lot of people interpreted this as being the official statement of the U.S. government," Walter Willet, chair of the Harvard Department of Nutrition, told Nature. Willet has not been shy about criticizing Flegal's work, declaring to NPR in 2013 that it was "a pile of rubbish, and no one should waste their time reading it."

Recent research has debunked all sorts of aspects of the supposed paradox. Using data from more than 225,000 long-term study participants, a 2017 study in the Annals of Internal Medicine showed that greater BMI was associated with greater risk of death from all causes, and a greater risk of dying specifically from heart disease; the association held up across sexes and age groups. Another 2017 study showed no obesity paradox when looking at new cases of cardiovascular disease.

Some scientists raised questions about Flegal's research from the beginning. "Closer examination of [obesity paradox] studies raises important questions on the validity of the paradox," stated a paper published in the American Journal of Cardiology in 2006.

"There is compelling evidence that the obesity paradox is not a real biological finding at all but just sloppy science," Boston University professor Andrew Stokes told Vox in 2015.