Harvard University researchers' dire predictions claim that America's obesity epidemic won't plateau until at least 42 percent of adults are obese.
The estimate has been derived by applying mathematical modeling to 40 years of Framingham Heart Study data.
The work runs counter to recent assertions by some experts that the obesity rate, which has been at 34 percent for the past five years, may have peaked.
An additional 34 percent of American adults are overweight but not obese, according to the government's Centers for Disease Control and Prevention.
The Harvard scientists said that their modeling shows that the proliferation of obesity among American adults in recent decades owes in large part to its accelerating spread via 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," said lead author Alison L. Hill, of the Harvard University.
"Specifically, the rate of weight gain due to social transmission has grown quite rapidly," said Hill.
The projections by Hill and colleagues have suggested the U.S. population may not reach this level for another 40 years, making the future rate of increase much more gradual than over the past 40 years.
The researchers broke down the spread of obesity into three components:
the rate at which obesity has spread through social networks, via transfer from person to person;the rate of non-social transmission of obesity, such as through easier access to unhealthy foods or increasingly sedentary lifestyles;the rate of "recovery" from obesity, defined as weight loss sufficient to push body mass index (BMI) back below 30.
"We find that while non-social transmission of obesity remains the most important component in its spread, social transmission of obesity has grown much faster in the last four decades," said David G. Rand, a research scientist in \Harvard's Department of Psychology.
Hill, Rand, and colleagues found that a non-obese American adult has a two percent chance of becoming obese in any given year-a figure that has risen in recent decades-and that this number rises by 0.4 percentage points with each obese social contact, meaning that five obese contacts doubles the risk of becoming obese.
By comparison, an obese adult has a four percent chance of losing enough weight to fall back to merely "overweight" in any given year. This figure has remained essentially constant since 1971.
The findings were published in the journal PLoS Computational Biology.