One out of every nine people now receives food stamps in the U.S. And two thirds of Americans are either overweight or obese. A new scientific study links these startling figures and suggests that food stamps may actually be a risk factor for obesity.

Participants in the U.S. Food Stamp Program have, on average, a body mass index (BMI) more than one point higher than nonusers, according to research published in the current issue of Economics and Human Biology. This difference was especially high for women: those buying their food with stamps carried around an average of 5.8 pounds more body weight. The researchers also found that BMI rose higher the longer participants received the stamps.

The findings came from an analysis of some 4,000 enrollees in federal food stamp programs who were compared with nearly 6,000 people not using food stamps, along with variables including BMI, race and other socioeconomic factors. All participants were randomly selected in 1979 to be part of the National Longitudinal Survey of Youth.

"Every way we looked at the data, it was clear that the use of food stamps was associated with weight gain," Jay Zagorsky, co-author of the study and research scientist at The Ohio State University's Center for Human Resource Research, said in a prepared statement.

But what could be causing this link? The researchers started digging and discovered that, according to government statistics, the average recipient received just $81 in food stamps per month in 2002 (the last year examined in this study).

"That figure was shocking to me," Zagorsky said. "I think it would be very difficult for a shopper to regularly buy healthy, nutritious food on that budget."

And the number of Americans eating on this budget is growing, surpassing 34 million for the first time in May. As Stacy Dean of the Center on Budget and Policy Priorities, a think tank, told Reuters, "Food stamp enrollment is rising because the economy is having a devastating impact on low-income families and they need this program to eat."

Various groups have posed possible solutions to the country's obesity epidemic. The Urban Institute, for example, has suggested "punishing" bad choices through a tax on fattening foods. Zagorsky, however, suggests a "positive reinforcement" approach: modify the food stamp program to include incentives to eat healthier.

Some cities are already doing just that. In Boston, "Bounty Bucks" double the value of food stamps at most local farmers' markets. Portable credit card readers at these markets allow shoppers to swipe their benefit cards to receive $20 in vouchers for every $10 in food stamps, The Boston Globe reports.

"It provides healthy, locally grown food to those who need it the most," Michel Nischan, president of Wholesome Wave, told the Globe. "It also benefits the farmers who grow the food."

Picture by clementine gallot via Flickr