Researchers claim in the new study that the obesity paradox has existed as a theory because of biases in data analysis. Photo by Ljupco Smokovski/Shutterstock

PHILADELPHIA, Oct. 13 (UPI) -- Although studies have shown obese and overweight people with cardiovascular disease, or CVD, outlive normal weight people with the disease, researchers at the University of Pennsylvania have shown this isn't true when considering weight history and smoking status.

The researchers say the new study disproves the obesity paradox, a theory suggesting obesity offers protection from certain chronic diseases.


Dr. Andrew Stokes, an assistant professor of global health at Boston University, said the paradox exists because research on it has generally only factored in weight at the time of a survey -- which he said in a press release "would be like classifying a lifelong smoker who quit the day before the survey as a non-smoker, even though we know that if you're a lifelong smoker you carry those risks over even if you stop smoking."

"There's every reason to imagine that clinicians are at least confused," said Dr. Samuel Preston, a sociology professor at the University of Pennsylvania, "and in some cases, are believing that being overweight or obese is a good thing among people with cardiovascular disease, diabetes and other conditions for which a paradox has been demonstrated."

Stokes and Preston considered data for 30,400 people collected as part of the National Health and Nutrition Examination Survey between 1988 and 2011. Of those survey participants, 3,388 had CVD.

The researchers found that 64 percent of the people who were normal weight and been diagnosed with CVD had previously been overweight or obese. Including these individuals in the normal weight group deceptively showed that fewer obese people had died of CVD, the researchers wrote in the study, despite their conditions likely being influenced by extra weight they'd lost after developing CVD or other conditions.

The same was found to be true when considering for people who smoke, a group that overall is less likely to be obese. When the researchers limited the pool of participants to non-smokers, they reported the link between normal weight and CVD decreased as well.

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"It's conceivable that there are health advantages [to obesity]," Preston said. "But we show they are overwhelmed by the disadvantages of being obese, once you control for these two sources of bias."

The study is published in the journal Obesity.