The card machine may be a dieter's natural enemy.

RODALE NEWS, EMMAUS, PA—In the eternal battle against America's bulging waistlines, the focus is often on what we're buying and where we're spending our food dollars. But not much interest has been paid to how we're paying for all that sugar, fat, and salt.

A new study published in the Journal of Consumer Research has found that one possible solution to encouraging people to make healthy food choices is to have them stick to paying with cash. The study found that people who use cash are less likely to spend money on unhealthy foods than people who pay with credit cards, and much of that has to do with our unwillingness to part with cash. "People have looked at how different modes of payments affect consumers, and what is generally being found is the notion that cash is more painful than other modes of payment," says Manoj Thomas, PhD, assistant professor of marketing at Cornell University's S. C. Johnson Graduate School of Management and lead author of the new study. "And that pain of paying curbs your impulsiveness and makes you less likely to buy those unhealthy products."

THE DETAILS: In four separate experiments, Thomas and his coauthors tested people's shopping habits, comparing what they bought with the method of payment used. In the first experiment, the authors collected grocery-shopping information from 1,000 single-member households for a period of six months, during which time the shoppers' food purchases were analyzed as well as their method of payment. Shoppers who paid with cash were less likely to have purchased unhealthy foods (such as cookies, candies, and baked goods) than the people who paid with credit or debit cards.

The second experiment was designed to replicate the first, but in a laboratory setting. The experiment included 151 college students who were shown 20 items, half of which were healthy and the other half unhealthy, along with a price. Half of the students were told they could only pay with cash, while the other students were allowed to pay with either credit cards or cash. Those who paid with cash spent only about $10 on unhealthy foods, while those in the second group spent $14; both groups, however, spent the same amount of money on healthy foods. Students in both groups also spent less time deliberating over unhealthy foods than they did over healthy food purchases, suggesting that unhealthy food purchases really are impulse buys and not planned.

The third experiment was similar to the second but was conducted on an online market-research panel of everyday consumers. As with the previous two experiments, cash payers spent less money on unhealthy items than credit-card users, but both groups spent roughly the same amount on healthy items. However, this time, the shoppers were asked whether they regretted buying any of the unhealthy goods. Cash shoppers were more likely to regret buying the unhealthy foods than credit-card shoppers were.

The final experiment was designed to test whether someone's method of payment was a reflection on their overall outlook on money, in this case, whether tightwads were more likely to use cash and, thus, spend less on unhealthy food than spendthrifts. A group of 125 college students repeated the 20-item fake shopping spree, after which they filled out a survey that designated each student a tightwad or a spendthrift. Regardless of their financial personality, both tightwads and spendthrifts fell prey to the cash versus credit-card mentality; cash payers, regardless of financial habits, spent less on unhealthy food than credit-card users.