A new study out of Harvard University predicts that adult obesity in the United States will not level off until it hits about 42%. The researchers arrived at the estimate by projecting from data from the Framingham Heart Study. They also noted a new factor adding to rising obesity: social contagion.

Your chances of becoming obese increase by 0.4 percentage points with each obese social contact you have. So having five obese friends or colleagues can double your risk of becoming obese.

The researchers make special mention of obesity's "infectious character," the way having overweight friends greatly increases the chances that you will be overweight. Your chances of becoming obese increase by 0.4 percentage points with each obese social contact you have. So having five obese friends or colleagues can double your risk of becoming obese.

Of course, social contacts and social contagion are only part of the rising rates of obesity. The authors suggest other familiar factors contribute: easy access to unhealthy foods, increasing rates of sedentary behavior and the less-than-stellar "rate of recovery" from obesity, meaning a sustained weight loss that brings a person’s BMI back below 30.

In any given year about 2% of adults are at risk of becoming obese according to the researchers. This figure has risen substantially in recent decades and the rate escalates with each additional obese social contact. The message seems to be that moving to a state of obesity is dramatically impacted by whether or not your significant social contacts are obese.

The study was pubished in the November 4th issue of the journal PLoS Computational Biology.