New Study Disputes Validity of the "Obesity Paradox"

Despite past research showing that obese or overweight individuals with cardiovascular disease (CVD) tend to live longer than normal weight people with CVD, obesity is harmful to those with the disease, according to a new study.

Researchers from the University of Pennsylvania and Boston University analyzed data from more than 30,400 participants from the National Health and Nutrition Examination Survey, conducted between the years 1988 and 2011. Among these participants, 3,388 had cardiovascular disease.

Fitness Vs. Fatness: The Obesity Paradox
New Study Questions “Obesity Paradox”

The authors note that many studies find an association between excess weight and better survival among individuals with cardiovascular disease, and sought to see whether this “obesity paradox” can be explained by biases. Studies of the mortality consequences of obesity, however, are subject to 2 major biases, the authors wrote: reverse causation and confounding by smoking. These biases are typically enhanced when attention is confined to individuals who have entered a disease state, according to the researchers, who note that whether the obesity paradox is a product of actual protection afforded by adiposity or of statistical biases has important clinical implications.

For this study, the authors chose to include weight history in their evaluation of participants, which they say allowed them to identify a control group of individuals who had always maintained a normal weight and were considered at low risk for disease. When accounting for weight history—as well as considering weight at the time of the survey and adding smoking as a factor—the investigators found that the mortality advantage that has been seen in past studies among overweight or obese individuals with CVD was eliminated in this analysis.

Ultimately, the findings “provide support for the hypothesis that lower mortality among individuals with CVD and overweight/obesity is a product of biases involving reverse causation and confounding by smoking,” the investigators wrote.  

—Mark McGraw


Stokes A, Preston S. Smoking and reverse causation create an obesity paradox in cardiovascular disease. Obesity. 2015.