The research also shows that if nothing changes significantly in the environment and culture in the USA, about 42% of adults will be obese in about 40 years and then the obesity rate will level off.
About a third of Americans are obese -- that is, roughly 30 or more pounds over a healthy weight. Those extra pounds increase their risk of developing type 2 diabetes, heart disease and many types of cancer.
After decades of skyrocketing growth in obesity, some experts have suggested that the rate may be leveling off. But Harvard researchers, in an effort to come up with a best-case scenario for the obesity epidemic, came to the 42% projection by applying an infectious-disease mathematical model to data from the Framingham Heart Study.
Their findings are reported online in the journal PLoS Computational Biology.
"We find that having four obese friends doubled people's chance of becoming obese compared to people with no obese friends," says Alison Hill, the study's lead author and a Harvard researcher.