A fleeting thought about a handful of M&M's might be enough to derail your diet. But imagining yourself eating the candy-covered chocolates in painstaking detail could actually make you want them less.
Obsessing about a particular food in a particular way appeared to dampen its appeal in an unusual study that demonstrates that merely thinking about a food - not actually seeing, touching, smelling or tasting it - can help sate hunger through a process called habituation.
In an experiment described in the journal Science, researchers asked volunteers to devote about a minute and a half to methodically imagining chewing and swallowing 30 M&M's, one after another after another.
Then, when presented with a bowl of actual M&M's, those volunteers ate about half as many candies as volunteers who imagined eating only three M&M's, or none at all.
The finding challenges the conventional wisdom that thinking about a food makes you eat more of it, said study leader Carey Morewedge, a professor of social and decision sciences at Carnegie Mellon University in Pittsburgh.
"Thought suppression tends to sensitize people to craving," he said. "A better way to deal with cravings might be to imagine indulging them."
Morewedge said he believes imaginary eating works because it triggers habituation, the psychological phenomenon that explains why we are able to get used to things that initially seem annoying - the roar of an airplane engine, for instance, or dim light in a restaurant. It occurs when extended exposure to a stimulus decreases an organism's response to it, and many experts think it helps regulate eating.
Until now, it was believed that direct sensory input was necessary for habituation to kick in. But if it can be triggered through thought alone, there could be many ramifications for dieters.
For starters, "avoid buffets," said Frances McSweeney, a professor of psychology at Washington State University who studies habituation and eating but wasn't involved in the study. "If you want to eat less, don't have a variety of foods available" because that makes it harder to habituate to any one of them.
The finding also suggests that people should also eat in a quiet place - not in front of the TV or at a sidewalk cafe - because outside stimuli can also disrupt habituation, she said.
"This helps to give us more insight into how we might be able to use the mind to manage our appetites," said Melinda Johnson, a registered dietitian and lecturer at Arizona State University in Tempe.
Morewedge and his team conducted five experiments. In the first, subjects were instructed to imagine performing 33 repetitive actions - either inserting a quarter into a laundry machine or eating an M&M, which involve similar motions.
Using computer images of quarters and M&M's to guide them through the exercise, one group visualized inserting quarters 33 times. Another group imagined inserting quarters 30 times and eating M&M's three times. A third group imagined inserting quarters 3 times and eating M&M's 30 times.
Then all participants were offered a real bowl of M&M's and invited to eat as many as they wanted. Those who spent the most time imagining eating M&M's ate 47 percent less, on average, than subjects who imagined eating three M&M's and 46 percent less, on average, than those who didn't imagine eating any M&M's.
Subsequent experiments tested whether imagining moving M&M's had the same effect as imagining eating them (it didn't) and whether imagining eating M&M's might suppress consumption of a different food, cheddar cheese cubes (again, it didn't - though imagining eating cheese did).
Throughout the experiment, Morewedge said, the team directed test subjects to keep their minds focused on the repetitive aspects of eating - looking at a cube of cheese, picking up the cube of cheese, lifting the cube of cheese to the lips, placing the cube of cheese on the tongue, chewing the cube of cheese, swallowing the cube of cheese, looking at the next cube of cheese, and so on.
Without such instruction, he said, habituation would be unlikely. "When you just tell people to imagine a steak," he said, "a flood of stimuli come through."
Of course, the rigors of this type of exercise might make it difficult for everyday dieters. "It is a very tedious thing to put into practice," Johnson said, especially since habituation is food-specific. "How do we apply the practice to overeating in general?"