The Surprising Way Reusable Bags Can Make You Buy More Junk Food

Bringing your own reusable grocery bags always seems like a huge win—for you and the environment—right? But according to a new study, that sense of accomplishment and pride you get from forgoing plastic bags may lead you to make poor food choices.

Researchers at Harvard Business School looked at the shopping receipts from one location of a major grocery store chain in California, and analyzed purchases based on whether they brought reusable bags or stuck with the store-provided plastic ones.

It's not surprising that those who toted their own bags to the store purchased more organic foods than non-organic. But the researchers also found that those who brought bags from home were much more likely to pick up junk foods like ice cream, candy, chips, and cookies.

“It was clear that shoppers who brought their own bags were more likely to replace non-organic versions of goods like milk with organic versions,” Uma Karmarkar, assistant professor of marketing at Harvard Business School and co-author of the study told the Harvard Business Review. “So one green action led to another. But those same people were also more likely to buy [junk food]. They weren’t replacing other items with junk food, as they did with organic food. They were just adding it to their carts.”

Karmarkar and her co-author, Bryan Bollinger, theorize that this is because shoppers feel like they can reward themselves for helping the environment.

“You give yourself a cookie,” she told the Harvard Business Review. “In this case literally. If I behave well in one situation, I give myself license to misbehave in another, unrelated situation. In this case bringing a bag makes you think you’re environmentally friendly, so you get some ice cream.”

But this doesn’t mean you should forgo helping the environment for the sake of your waistline. Karmarkar believes that as bringing reusable bags becomes more widespread, this trend will drop off, citing the practice of recycling plastic bottles as an example.

“It used to be that you felt as if you were doing a good thing by recycling bottles,” she said. “Now it’s to the point were you don’t get a cookie for recycling them.”

The researchers found that when people were required to BYOB because of plastic-bag bans, the junk food purchases stopped, while the organic purchases continued. (California and Washington, D.C. as well as a few select counties across the country, have enacted such legislation, set to go into effect starting later this year.)

“Basically, if it’s compulsory, we don’t get that jolt of affirmation about being a good person,” Karmarkar told the Harvard Business Review.

Everyone deserves a treat now and again, but pay close attention to what you're loading into your cart next time you're at the store. Your reusable bags really are great for the planet, but they definitely don't negate the health effects of too much added sugar.

And one more note: make sure you're cleaning them every so often. Research shows that they can be a hotbed for salmonella and E. coli. An outbreak of the gastrointestinal illness norovirus was even traced back to the environmentally-friendly totes back in 2012.