Do Reusable Bags Affect Your Diet?
A new study suggests that bringing your own reusable shopping bags to the grocery store may influence what you decide to buy.
22 Apr 2015   Christian Camerota

It turns out you aren’t just what you eat. How you carry things also says a bit about how you care for yourself and the world around you.

Harvard Business School assistant professor Uma Karmarkar spent time unpacking people’s grocery purchases to see if she could learn more about what drives their decisions when they’re behind the wobbly wheels of their shopping carts. Specifically, she wanted to know what happens when a previously predictable consumer experience is disrupted.

“For most people in the U.S., bringing your own reusable bags to the store requires you to think where you didn’t have to before,” Karmarkar said. “You’re trying to do something good for the environment for all the best reasons. But the fact is that it’s a new behavior added into a place that has become habitual. Our question was: do these environmental actions have any downstream effects on the way people respond to what they see in the store?”

The short answer is yes. Karmarkar and coauthor Bryan Bollinger’s study discovered that bringing their own bags made consumers more likely to choose organic products over regular ones on those trips, which perhaps makes sense given the environmentally-minded nature of both decisions. More surprising, however, was that those same consumers tended to reward themselves at the end of their shopping trip by treating themselves to small indulgences like cookies or chips.

“It’s not entirely clear whether the choice is conscious or unconscious,” Karmarkar said. “The literature and our data suggest that it’s an unconscious decision. No one is saying, outright, ‘I brought my bags, I can have a cookie,’ and these indulgences aren’t necessarily massive. And yet, there is a cohesiveness between the two decisions. These simple things we do in our lives do have downstream effects that we may not have expected.”

It’s no surprise that Karmarkar chose to study supermarkets, given her expertise in consumer behavior and the fact that grocery stores offer an abundance of quantifiable consumer decision-making data on a very large scale. For the first study in the paper, Karmarkar and Bollinger looked at almost 1 million purchases by around 6,000 households during a two-year period at a large grocery chain in California, data that was all ripe for analyzing. They supported and extended their findings from this data by running a series of experiments in which people were assigned to imagine shopping with or without reusable bags.

“The lovely part of grocery shopping is that it’s such a common experience,” Karmarkar said. “Everyone’s doing the same thing, and yet there are still differences in the individual experiences, and the in-store messaging is so intense. Something we all do once a week has so much going on at a more nuanced level.”


The study has interesting implications for marketers, who have already learned to stockpile low-priced impulse items near cash registers, where consumers represent a captive audience while waiting in line. Grocers could consider the link between reusable bags and organic choices and co-promote those items, or even work to help certain consumers reconceive of healthier products as indulgences and so induce their purchase more often.

But more interesting for Karmarkar is the extent to which further research could elaborate on the findings, such as how consumers view and treat something like an organic cookie that could be considered both an indulgence and a conscientious purchase. She’s also interested in the broader implications for the environment and store owners’ responsibility in that regard.

“What’s interesting, environmentally, is how one might develop policies around these findings,” she said. “Recycling, for instance, was a behavior that people had to learn. We’re in the adoption phase with reusable bags right now where things are in flux. But once bringing your bag becomes second nature, it would be fascinating to see if that influences the kinds of effects we saw.”


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