Plastic-bag bans are currently on the books in about a dozen U.S. cities—a dozen cities that will be seeing fewer bags clustered in rivers, tangled in tree branches, and clogging storm drains. Those cities might also start noticing an uptick in junk-food purchases.
That’s the implication of a study that tried to figure out whether people’s shopping habits changed when they brought their own grocery bags. For the study, Uma Karmarkar, a professor of marketing at Harvard Business School, and Bryan Bollinger, a professor of marketing at Duke’s Fuqua School of Business, analyzed loyalty-card data from some 140,000 trips to a single grocery store in California in the mid-2000s. They found that people are 13 percent more likely to buy organic products when they bring their own bags—and they’re also 7 percent more likely to buy junk food, such as chips and cookies.
To explain these changes, the researchers propose two theories, one for the boost in organic purchases and one for the boost in what they call indulgent purchases—chips and cookies. The first explanation is the simpler of the two: People who walk into a grocery store with canvas bags in hand are already in a greener mindset, and this affects their purchasing decisions. Although many people don’t even know precisely what “organic” means, they still perceive buying organic as doing a favor for the environment, so it makes sense that their environmentally-friendly mentality might lead them to be more open to purchasing organic foods.