It's not likely that credit card companies will be forced to post the warning that using these cards could be hazardous to your waistline. But if researchers from Cornell University and the State University of New York are right, they may have uncovered a link between credit card use and obesity.

A new study published in the Journal of Consumer Research shows that people who use credit cards for food tend to buy more junk food than those who use cash.

This could be a major discovery for the two-out-of three Americans who are either obese or overweight. They could kill two birds with one stone just by not using credit cards. Lose weight and reduce their debt.

Authors of the grocery study say they originally tried to find the link between unhealthy food purchases and payment methods. They began by collecting shopping data from an unnamed American store chain. They found that 41% used credit cards, 9% used debit cards, and the remaining 50% paid cash. Further study showed that shoppers who paid with plastic spent far more and bought more junk and impulse items than customers who paid cash.

To replicate their findings, the researchers conducted a similar test on students, who were told that a large retail chain was opening a store in town and wanted to understand what shoppers buy during a typical trip.

Computer screens showed subjects 10 healthy items such as oatmeal and 10 junk or unhealthy items such as Oreo cookies. Credit-card shoppers ended up with about three unhealthy items costing $14.07 while cash shoppers bought only two healthy unhealthy items and spent $9.89 on them.

Next, according to Smart Money magazine, the researchers performed a similar experiment on consumers referred by a market research group, but this time they surveyed participants on their feelings.

Card shoppers again spent far more on junk than cash shoppers, with no difference in spending on healthy food. Both groups reported paying attention to prices and being aware of the nutritional merits of the items they chose. Members of the cash group, however, found paying far more painful.