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Obesity myth debunked

Being overweight increases the chances of premature death

In short, like smoking, the health problems associated with underweight, overweight and obesity are substantial but potentially preventable

Although people accept that obesity can shorten a person's life span, scientists have debated whether the weight category between normal and obese is, in fact, a health risk. However, according to a study published in The Lancet, on behalf of The Global BMI Mortality Collaboration, overweight and obesity were strongly connected to coronary heart disease, stroke and respiratory disease death, and were moderately linked to cancer mortality.

In their study, Body-mass index and all-cause mortality: individual-participant-data meta-analysis of 239 prospective studies in four continents’, the researchers conducted individual-participant data meta-analyses of prospective studies of BMI, to help assess their relevance to mortality in different populations, thereby limiting confounding and reverse causality by restricting analyses to never-smokers and excluding pre-existing disease and the first five years of follow-up.

Of 10,625,411 participants in Asia, Australia and New Zealand, Europe, and North America from 239 prospective studies (median follow-up 13·7 years, IQR 11·4–14·7), 3,951,455 people in 189 studies were never-smokers without chronic diseases at recruitment who survived five years, of whom 385 879 died. The primary analyses are of these deaths, and study, age, and sex adjusted hazard ratios (HRs), relative to BMI22.5–<25.0.

Using an accepted but imperfect measure, the study was able to find a connection between premature death and being overweight. The proportion of premature deaths that could be avoided with a healthy weight (between BMI 18.5 and 25) is about one in five in North America, one in six in Australia and New Zealand, one in seven in Europe and one in 20 in East Asia.

In short, like smoking, the health problems associated with underweight, overweight and obesity are substantial but potentially preventable.

These findings contradict a 2013 review article in the Journal of the American Medical Association, which found that being overweight actually adds to one's life span, and "grade 1 obesity" (BMI 30-35) did not increase mortality. The JAMA article was based on a review of 97 studies with 2.9 million participants.

"Our study was able to reproduce [the JAMA review's] findings when conducting crude analyses with inadequate control of reverse causality, but not when we conducted appropriately strict analyses," the Lancet paper stated.

Being underweight, according to the study, was associated with substantially higher respiratory disease mortality and somewhat higher death rates from coronary heart disease, stroke and cancer. These findings held true in Asia, Australia, New Zealand, Europe and North America.

"The health risk associated with obesity is thought to be driven by abdominal fat," said Dr Jonathan Samet holder of the Flora L Thornton Chair in Preventive Medicine at the Keck School of Medicine of USC, an author of the study. "BMI is an imperfect measure of fat in someone's belly. There are more gold standard ways to measure fat, but that can't be done for 10.6 billion people."

"Physicians should identify being overweight as posing a risk to health," added Samet. "Increasing the risk of dying is a powerful indicator of health. The new results on overweight should be strong motivation for people to return to a healthy weight."

This study was funded by the UK Medical Research Council, British Heart Foundation, National Institute for Health Research and the US National Institutes of Health.

To access this paper, please click here

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