Why We Wolf Down Junk

By Suzanne Wu

Habit makes bad food too easy to swallow.

Illustration by Hadley HooperIllustration by Hadley Hooper

DO YOU ALWAYS GET POPCORN at the movies? Or snack on chips and cookies while watching TV? A new study by USC psychologists helps explain why these bad habits are so hard to break – even when the food tastes lousy.

In an experiment, researchers gave moviegoers a bucket of popcorn as they entered a theatre. Some buckets contained freshly popped kernels; others contained week-old stale kernels. When the movie ended, researchers measured how much popcorn got eaten, and by whom.

Turns out moviegoers who don’t usually buy popcorn at the movies ate far less stale popcorn than fresh popcorn. The week-old popcorn just didn’t taste good to them.

But moviegoers who routinely munch on popcorn weren’t as discriminating. They ate about the same amount of popcorn whether it was fresh or stale. In other words, for those in the habit of eating popcorn at the movies, taste made no difference.

The data undercuts a common assumption among dieters. “People believe their eating behavior is largely activated by how food tastes,” says Wendy Wood, Provost Professor of Psychology and Business at the USC Dornsife College of Letters, Arts and Sciences. “Nobody likes cold, spongy, week-old popcorn. But once we’ve formed an eating habit, we no longer care whether the food tastes good. We’ll eat exactly the same amount, whether it’s fresh or stale.”

The study, published in the journal Personality and Social Psychology Bulletin, has important implications for understanding overeating and the conditions that may cause people to eat even when they aren’t hungry or don’t like a specific food.

“When we’ve repeatedly eaten a particular food in a particular environment, our brain comes to associate the food with that environment and makes us keep eating as long as those environmental cues are present,” says lead author David Neal, who was a USC psychology professor when the research was conducted and now heads a social and consumer research firm.

Researchers factored in hunger and whether the participants liked the popcorn they received. They also gave popcorn to a control group that watched movie clips in a meeting room, rather than a theatre.

In the meeting room, it mattered a lot if the popcorn tasted good. Outside of a theatre context, even habitual movie popcorn eaters ate much less stale popcorn than fresh, demonstrating how environmental cues can trigger automatic eating behavior.

“The results show just how powerful our environment can be in triggering unhealthy behavior,” Neal says. “Sometimes willpower and good intentions are not enough, and we need to trick our brains by controlling the environment instead.”

In a related experiment, researchers tested a simple disruption of automatic eating habits. Again using stale and fresh popcorn, they asked participants about to enter a film screening to eat popcorn either with their dominant or nondominant hand.

Using the nondominant hand seemed to disrupt habitual eating and cause people to pay attention to what they were eating. As a result, they ate much less of the stale than the fresh popcorn. This method worked even for those with strong eating habits.

“It’s not always feasible for dieters to avoid or alter the environments in which they typically overeat,” Wood says. “More feasible, perhaps, is for dieters to actively disrupt the established patterns of how they eat through simple techniques, such as switching the hand they use to eat.”