Do shoppers with reusable bags buy more junk food?

What's the connection between people that use reusable grocery bags and the food they buy? Are people inclined to treat themselves with junk food when they feel they've done a good thing by bringing their own bag?

These questions are at the core of research conducted by a Harvard Business School assistant marketing professor and her research partner from Duke's Fuqua School of Business.

Harvard's Uma Karmarkar and Duke's Bryan Bollinger dissected the grocery bills of thousands of shoppers in California. The receipts highlighted discounts people that brought their own reusable bags received, so the researchers were able to see how these shoppers' carts compared to those that didn't bring a bag.

A recent Harvard Business Review article features an interview with Karmarkar and provides insights on what would appear to be contradictory behaviours. Shoppers that use reusable bags are more likely to buy organic versions, yet they were also more likely to buy things like chips, candy bars and ice cream.

Their research, which used quantitative data pulled from loyalty cards over a long period of time, even got as detailed as showing when individuals brought bags versus when they didn't. This allowed for comparisons between when the same people did or didn't bring their bags and how that impacted their purchases.

One standout finding shows that when people brought their reusable bag, it made them think they were environmentally friendly, so they'd get a sweet treat to reward themselves. "You feel you've earned it," says Karmarkar.

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