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Obesity Epidemic Influenced by Social Transmission

Most obesity due to individual factors, but social 'contagion' contributes to the epidemic

FRIDAY, Nov. 5 (HealthDay News) -- America's obesity epidemic is expected to continue to worsen until at least 42 percent of all adults are obese, and "social contagion" of obesity is in important factor, according to research published online Nov. 4 in PLoS Computational Biology.

Alison L. Hill, of Harvard University in Cambridge, Mass., and colleagues used a novel theoretical framework for studying behavioral phenomena -- in this case, obesity -- which have been found to spread interpersonally through social networks, similar to the spread of infectious diseases. Into their model, the researchers factored the rate at which obesity has spread through social networks, the rate of nonsocial transmission of obesity -- such as through easier access to unhealthy foods and increasingly sedentary lifestyles -- and the rate of recovery from obesity, as measured by an individual's ability to decrease their body mass index below 30 kg/m².

The model showed that a non-obese American adult has a 2 percent chance per year of becoming obese; this rate increases by 0.4 percent for each obese social contact. The rate of obesity recovery is 4 percent per year, and does not depend on the number of non-obese contacts. The model contradicts recent expert opinion that the obesity rate, which has remained at 34 percent for the past five years, has reached its peak, and predicts an eventual obesity prevalence of about 42 percent.

"Here we show that the dominant process in the increasing prevalence of obesity is contact-independent weight gain; however, the rate of interpersonal transmission [contributes] significantly to the overall prevalence and appears to be increasing steadily over time," the authors write. "Thus, consideration of social transmission and network effects is an important issue for health and policy professionals."

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