Researchers are projecting that 40 years from now America’s obesity epidemic will finally plateau -- with 42 percent of adults considered obese. And obesity can actually be contagious, they added.
The recent findings were derived by applying mathematical modeling to 40 years of Framingham Heart Study data, and published in the PLoS Computational Biology journal.
The estimate runs counter to other experts’ assertions that the obesity rate may have already peaked. The rate has been at 34 percent for the past five years, according to the Centers for Disease Control and Prevention, with an additional 34 percent of American adults considered overweight but not obese. (Click here to see how the CDC defines those terms.)
The Harvard scientists said their modeling shows the proliferation of obesity among American adults in recent decades owes its acceleration to social networks.
"Our analysis suggests that while people have gotten better at gaining weight since 1971, they haven't gotten any better at losing weight. Specifically, the rate of weight gain due to social transmission has grown quite rapidly," according to lead author Alison L. Hill, a graduate student in Harvard's Program for Evolutionary Dynamics, Biophysics Program, and at the Harvard-MIT Division of Health Sciences and Technology.
The study showed obese people have the potential to create a ripple effect among their non-obese peers, the report said. So the more non-obese people an obese person comes into contact with, the greater the chance those people will become obese.
Researchers based their findings on a model of obesity's spread through social networks, which was similar to models used to trace the spread of infectious diseases like the flu. They found the obesity rate is affected by three factors:
>> person-to-person contact through social networks,
>> personal factors like diet and exercise, and
>> the rate at which obese people lose weight.
After analyzing 40 years of data from 7,500 people in the 62-year-old Framingham Heart Study, researchers found the average person has a 2 percent chance of becoming obese in any given year, due to personal factors such as an unhealthy diet or lack of exercise. That chance increases by 0.5 percent for every obese family member, friend or coworker a person has regular contact with, the study said.
An obese person has a 4 percent chance of losing enough weight to no longer be considered obese in any given year, the study said.
"Maybe it's mimicking behavior or adopting similar lifestyles, or changing what you consider to be a normal and acceptable weight for yourself based on the weight of people around you," Hill said in the report. "It's most likely to be some social influence."