If you’re trying to make better food choices at the grocery store, you may want to try leaving the plastic at home and paying with cash. A new study from researchers at Cornell and SUNY reports that people buy less junk food when they pay with cash, as handing over bills is "psychologically more painful" than paying with credit.

Shopping carts were filled with more junk food and impulse purchases when shoppers used credit or debit cards. In contrast, paying with cash was linked to fewer unhealthy food items in the cart.

The researchers followed 1,000 families as they shopped for food over a period of six months. They tracked what the participants added to their carts and the methods they used to pay for their groceries. The results showed that shopping carts were filled with more junk food and impulse purchases when shoppers used credit or debit cards to pay for the purchases. In contrast, paying with cash was linked to fewer unhealthy food items in the cart.

Why is this? The authors’ follow-up study showed that "cash payments are psychologically more painful than card payments, and this pain of payment can curb the impulsive responses to buy unhealthy food items." And people who have paid with cash customarily over a long period of time are apparently more sensitive to this "vice-regulation" effect. The authors write that in contrast to cash payments, "[c]redit card payments... are relatively painless and weaken impulse control." In other words, if you don’t actually see the money changing hands as (one does not when credit or debit cards are used), you’re more likely to spend on unnecessary items, including junk food.

Is there a relationship between the rise in credit card spending and America’s expanding waistline? The authors suggest that there is a link, pointing out that 40% of grocery purchases are paid for with credit or debit cards these days. They write that "[t]he epidemic increase in obesity suggests that regulating impulsive purchases and consumption of unhealthy food products is a steep challenge for many consumers". Being aware of the credit-junk food phenomenon may help people make better choices at the grocery store. It can’t hurt to try leaving the cards at home and making a quick trip to the ATM before embarking on a grocery shopping excursion.

The study was published in the October 6, 2010 issue of the Journal of Consumer Research.