Want to shed some pounds? You can start by leaving the credit card at home.

A new study published in the Journal of Consumer Research found that people who purchase food with credit or debit cards are more likely to buy unhealthy food items than those who use cash to make the purchases.

Using data from a large grocery store chain, researchers from the State University of New York and Cornell University found that using plastic to pay had “a significant positive impact on the impulsiveness and unhealthiness of the basket.”

The researchers confirmed their findings in a series of laboratory experiments. In one, participants were told which forms of payment a ‘store’ accepted, and then asked to consider 10 “vice” products and 10 “virtue” products in a hypothetical shopping situation. “Participants spent more on impulsive vice products when the mode of payment was credit card than when it was cash,” they found.

So what is it about plastic that makes us go for junk food? The study points to two existing areas of research. The first body of evidence indicates that paying with debit or credit cards is less “painful” than paying with cash – that is, actually doling out a hunk of cash seems more “real” than just swiping a card. The result is that paying with a credit or debit card makes you more likely to buy on impulse, as we reported earlier this month.

The authors then point to another body of research that correlates impulsive spending with buying less healthy food items. Based on the existing findings, the authors conclude that “Some unhealthy food products trigger impulsive purchase urges because of the desire activated by emotive imagery and associated sensations.” The link, then, is impulse: People are more likely to grab unhealthy foods on impulse, and are then more likely to make the purchase if they’re using plastic instead of cash.

This makes sense, though I would suggest another possible explanation: People who pay for everything with plastic are inclined toward speed and convenience, and it’s a lot faster to buy a TV dinner than it is to buy fresh produce and cook something from scratch.

Whatever the cause, though, people looking to trim their waistlines – and fatten their bank accounts – would be well-served by paying with cash whenever possible.

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