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What's in a Number? Some Research Shows That a Lower B.M.I. Isn't Always Better.

Biased ideas about a link between body size and health have led many people to dismiss unexpected scientific findings.

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A focus on weight loss and body size took hold across the United States in the 1990s, and many medical experts began sounding an alarm: Being overweight would lead to premature death. Obesity does carry with it well-documented health risks, but some research has shown positive health outcomes associated with being slightly overweight. Those counterintuitive findings are sometimes labeled as an “obesity paradox” rather than a reason for further study.

In research over three decades, C.D.C. epidemiologist Katherine Flegal found that the connection between weight and health was more complicated than many Americans believe. When she broke down data from a large-scale analysis into the categories of underweight, overweight and obesity, she found something surprising: the number of premature deaths was lower than expected for people in the overweight category.

Her findings were met with skepticism by medical experts, but the results have held up under decades of scrutiny .“Our findings produced controversy because someone wanted a controversy,” Dr. Flegal told us.

‘I don’t think you should rule out the idea that our whole perspective has been wrong about this,’ she said.

“Myths, assumptions and biases are persistent and well documented in the contentious realm of obesity research,” Kelso Harper, the producer for this video, wrote in an article published today by Scientific American.

Dr. Flegal said societal weight stigma and the financial interests of the pharmaceutical and weight-loss industries combine to bolster such biases. “The whole area of body weight and obesity has become very, very difficult to study objectively,” she said. “There’s so much emotion, so many interests that are involved.”

Read More:The Weight Game: How Body-Size Bias Can Hold Back Health Science by Kelso Harper