New study suggests common sense bears out.

August 23, 2017

In 2013, a study came out that questioned a core health principle: what if being overweight, on its own, wasn’t actually unhealthy? As counterintuitive as it seemed, that’s what the new research suggested. A meta-analysis of existing studies, it found that participants with a BMI of 25 to 30 (above the optimal range) were less likely to prematurely die than those with a healthy BMI.

Around 70% of the U.S. adult population is either overweight or obese. The possibility that carrying around extra pounds wasn’t necessarily a red flag—that, in some cases, it could actually be a mark of longevity—was groundbreaking. The study immediately made headlines. From there, it rippled through the Internet, inspiring a slew of stories and anecdotes on the benefits of being “fat but fit.”

It also inspired a fiery debate among nutrition scientists. (The Atlantic has an excellent summary of the drama.) In short: the main criticism of the 2013 study was that it failed to account for participants’ weight history, which meant previously heavy people who lost weight due to illness were put in the “healthy weight” bucket, artificially inflating the risk of premature death for normal-weight people (while artificially decreasing it for their overweight peers).

After controlling for the above, a series of subsequent studies not only failed to find a protective benefit from being overweight, but actually found the opposite: the more an individual exceeds a healthy weight, the higher his or her risk of mortality from cardiovascular disease and certain cancers. (To be fair, other subsequent studies have found a protective relationship.) For many of these papers, nutrition scientists on the opposite side of the debate attacked the researcher’s methodology. (Bottom line: these are all observational studies that must contend with range of variables, which makes drawing clear-cut, replicable conclusions extremely difficult.)

This hasn’t stopped researchers from trying to refine their collection techniques. And so against this backdrop comes a new study on weight and health, one that comes decisively down on the side that carrying around extra pounds is unhealthy.

Published in the European Heart Journal, researchers tracked more than half a million people for over a decade. During that period, around 7,500 developed heart disease. Being overweight or obese at the start of the study significantly increased participants’ likelihood of falling into that camp. Importantly, this link remained even for those who were overweight or obese but metabolically healthy at the beginning of the study, i.e. they had healthy blood pressure, blood sugar, and cholesterol readings. After controlling for a variety of factors (including diet, alcohol intake, physical activity, and socio-economic status) these metabolically healthy overweight and obese individuals were a respective 26% and 28% more likely to develop heart disease than participants with similar readings and a healthy BMI.

The findings suggest obesity, in itself, increases the risk of developing health complications down the road, says Camille Lassale, an epidemiologist from Imperial College London’s School of Public Health (and one of the study’s authors). Her hypothesis is that for those who are overweight but metabolically healthy, the health impact of those extra pounds simply hasn’t caught up with them yet. “There is no such thing as ‘fit but fat,’” she says. “Health professionals should advise patients who carry extra weight to make lifestyle changes in order to return to a normal weight range.”

She understands that this isn’t easy news to hear. A growing body of research suggests losing weight alters the body’s metabolism, making it incredibly difficult to achieve, much less maintain, significant weight loss. “Most interventions aren’t successful,” she concedes. “Weight loss rarely lasts.”

Lassale’s next suggestion is a bit heartbreaking: as a society, perhaps we should focus on ensuring our children never become overweight and obese in the first place (and thus locked in a struggle with their metabolisms to achieve a healthy BMI).

Still, for anyone alarmed by the findings, Lassale urges a return to common sense. Yes, the study found that being overweight is linked with a higher risk of developing heart disease. But the corresponding coverage also mask a larger (if more consistent, and less headline-friendly) truth: for those looking to improve their health, focus on moving more and developing eating patterns that are balanced, full of variety, rich in plant-protein, and low in added sugars, saturated fats, and processed foods.

Yes, you could lose weight. But aside from that, you’ll likely improve your metabolic health, the most important indicator of subsequent heart disease, and of which weight is but one factor.

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