Even when people are hard at work, pictures of cookies, pizza, or ice cream can distract them—and these junk food images are almost twice as distracting as healthy food pictures, concludes a new Johns Hopkins University study. Researchers also found that after a few bites of candy, people found junk food no more interesting than kale.

The study—which underscores people's implicit bias for fatty, sugary foods and confirms the old adage about why you shouldn't go grocery shopping when you're hungry—is newly published in the journal Psychonomic Bulletin and Review.

"We wanted to see if pictures of food—particularly high-fat, high-calorie food—would be a distraction for people engaged in a complicated task," said co-author Howard Egeth, a professor in the Department of Psychological and Brain Sciences. "So we showed them carrots and apples, and it slowed them down. We showed them bicycles and thumb tacks, and it slowed them down. But when we showed them chocolate cake and hot dogs, these things slowed them down about twice as much."

First Egeth and lead author Corbin A. Cunningham, Distinguished Science of Learning Fellow in the Department of Psychological and Brain Sciences, created a complicated computer task where food was irrelevant and asked a group of participants to find the answers as quickly as possible. As the participants worked diligently, pictures flashed in the periphery of the screen—visible for only 125 milliseconds, which is too quick for people to fully realize what they just saw. The pictures were a mix of high-fat, high-calorie foods; healthy foods; or items that weren't food.

All the pictures distracted people from the task, but Cunningham and Egeth found that things such doughnuts, potato chips, cheese, and candy were about twice as distracting. The healthy food pictures—things like carrots, apples, and salads—were no more distracting to people than nonfoods like bicycles, lava lamps, and footballs.

Next, the researchers re-created the experiment, but had a new group of participants eat two fun-sized candy bars before starting the computer work. The researchers were surprised to find that after eating the chocolate, people didn't find the high-fat, high-calorie food images any more distracting than healthy foods or other pictures.

They wonder now whether less chocolate or even other snacks would have the same effect.

"I assume it was because it was a delicious, high-fat, chocolaty snack," Egeth said. "But what if we gave them an apple? What if we gave them a zero-calorie soda? What if we told the subjects they'd get money if they performed the task quickly, which would be a real incentive not to get distracted. Could junk food pictures override even that?"

Cunningham said the results strikingly demonstrate that even when food is entirely irrelevant, and even when people think they're working hard and concentrating, food has the power to sneak in and grab our attention—at least until we eat a little of it.

"What your grandmother might have told you about not going to the grocery store hungry seems to be true," Cunningham said. "You would probably make choices that you shouldn't or ordinarily wouldn't."