Scientists figured out what's making these California shoppers buy more junk food

To buy or not to buy that pint of Ben & Jerry’s ice cream?

It’s an all-too-familiar recurring dilemma that surfaces every grocery run. And if it’s not ice cream then it’s cookies, candy, chips, or something else that is delicious but also packed full of salt and sugar, which is neither good for your health or waste line.

But what makes you ultimately decide to buy, or pass, on the Chunky Monkey?

One reason could be if you’re bringing your own reusable bags to the grocery story, according to a recent study.

Uma Karmarkar, assistant professor of marketing at Harvard Business School, and her research partner Bryan Bollinger, at Duke’s Fugqua School of Business, studied two years and nearly 1 million grocery transactions (from loyalty-card data) of shopper’s purchasing habits from a major California grocery store chain.

They were also able to get information about the types of bags the shoppers were using: whether they were using plastic bags from the store or bringing their own, reusable bags.

“It was clear that shoppers who brought their own bags were more likely to replace nonorganic versions of goods like milk with organic versions,” Karmarkar told Harvard Business Review. “So one green action led to another. But those same people were also more likely to buy foods like ice cream, chips, candy bars, and cookies.”

While shoppers who brought their own bags were 0.25% more likely to buy organic food, they were 1.24% more likely to purchase junk food items. But why?

Well, people know they’re doing something good by using reusable grocery bags, and when we’re good we feel like we deserve a reward. Experts call this psychological reasoning “licensing.”

“If behave well in one situation, I give myself licence to misbehave in another, unrelated situation,” Karmarkar explained. “In this case bringing a bag makes you think you’re environmentally friendly, so you get some ice cream.”

Karmarkar makes a point to emphasise in the paper detailing the study that the results are strictly taken from California shoppers, and therefore are not a large enough sample to suggest that everyone who brings their own bags are more likely to buy junk food.

Shoppers on the East Coast for example may not be at risk of this unhealthy habit. However, considering the root cause for the habit seems to be behaviour and not location, it’s something to watch out for, at least. Karmarkar said that while this behavioural trait might be leading to unhealthy choices, it’s what makes us human:

“I think it’s fun that humans are like this, that these subtle subconscious effects can move our decisions around. It’s something that makes us interesting.”

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