Visit the grocery store on an empty stomach, and you will probably come home with a few things you had not planned to buy. But hunger pangs are not the only culprit behind impulse purchases. The location of store displays also influences our shopping choices—and may make or break some healthy eating habits.

The checkout area is a particular hotspot for junk food. Studies have found that the products most commonly found there are sugary and salty snacks—and a few studies have suggested that simply swapping in healthier options can shift customer behavior. A 2012 study in the Netherlands found that hospital workers were more likely to forgo junk food for healthy snacks when the latter were more readily available on canteen shelves, for example. In 2014 Norwegian and Icelandic researchers likewise found that replacing unhealthy items with healthy ones in the checkout area significantly increased last-minute sales of healthier foods.

These findings caught the attention of the New York City Department of Health and Mental Hygiene, which has been working with more than 1,000 store owners to encourage them to stock and promote nutritious foods. “We know that the food retail environment is full of cues meant to encourage consumption,” says Tamar Adjoian, a research scientist at the department. “Making healthy food more convenient or appealing can lead to increased sales of those products.”

Adjoian and her colleagues wondered if such findings would apply to their city's dense urban checkout areas, so they recruited three Bronx supermarkets for their own study. They gave one checkout line in each store a healthy makeover, replacing candy, cookies and other processed snacks with fruit, nuts and similar items containing 200 or fewer calories per serving. Then they recorded purchases over six three-hour periods in each store for two weeks.

Of the more than 2,100 shoppers they observed, just 4 percent bought anything from the checkout area. Among those who did, however, customers in the healthy lines purchased nutritious items more than twice as often as those in the standard lines—and they bought unhealthy items 40 percent less often. The findings were reported in September in the Journal of Nutrition Education and Behavior.

The potential impact may seem small, but Adjoian believes that converting more checkout lines would open customers' eyes to nutritious, lower-calorie foods. Health department officials are now exploring ways to expand healthy options at checkout aisles throughout New York City.