Reusable Shopping Bags Could Be Making You Buy Junk Food

Nothing says Functional Adult like getting your food supplies organised for the week ahead. Rolling down the supermarket aisle on a Sunday afternoon, armed with a list of ingredients for all the nourishing tagines and chilis you're going to make in bulk and assign to individual Tupperware containers takes Monica Geller-levels of pre-planning. Never mind that come Wednesday, you'll be sick of homemade curry and blow half of next week's budget on takeaway sushi.

But as you lug your grocery haul back in a reusable bag, you can be safe in the knowledge that your shopping trip is at least on the eco-friendly side. Maybe you're rocking one of Tesco's classic hessian numbers or went all out with an "I'm not a plastic bag" sack a few years ago. Even that ratty old tote bag you got at a marketing event once is its own stand against the tide of plastic bags that end up in landfill every year.

While no one can doubt your commitment to recycling (or organisational skills, future you will be grateful for all that frozen lasagne!), reusable shopping bags may be fueling unhealthy eating habits.

A study from academics at Harvard University and Duke University has found that choice of shopping bag can influence purchasing. Published in the Journal of Marketing, the study found that those who took their own reusable shopping bags to a supermarket were 33 percent more likely to purchase unhealthy snacks than those who used the plastic bags provided by the store.

While the researchers noted that reusable shopping bags can mean shoppers are more likely to purchase organic food, this may actually encourage them to buy junk food too.

Assistant professor of business administration at Harvard's Marketing unit and study co-author Uma Karmarkar explained that shoppers who bring their own bags and buy organic "often feel virtuous, because they are acting in an environmentally responsible way. That feeling easily persuades them that, because they are being good to the environment, they should treat themselves to cookies or potato crisps or some other product with lots of fat, salt, or sugar."

According to reusable shopping bag toters, if you eat buy organic greens and recycle, you deserve an appropriately deep-fried/chocolate-smothered reward.

The bad bag news doesn't stop there, either. Using loyalty card data from a California supermarket chain between May 2005 and March 2007, researchers found that bringing your own bags could also add to the cost of a weekly shop. Due to the increased likelihood of buying more expensive organic food when reusing a bag, around £8 ($12) was added to a family of four's bill for each weekly shop.

The study is the first to show a link between bringing your own grocery bags and changes in food purchasing behaviour. As Hawaii becomes the first state to ban plastic bags in grocery stores and a 5p tax is to be introduced on single-use plastic bags in the UK this October, it's also another layer to the debate on how we should be transporting our day-to-day supplies.