To Prevent Overeating, Think About Overeating

Imagine that you're eating your favorite food, perhaps a bloody steak or an obscenely large bar of chocolate. You're probably quite keen for an actual mouthful now. You may even have started to salivate. But wait - before you dash for the kitchen, imagine eating another one. And another one. In fact, picture yourself guzzling down thirty more. Do you still want a bite?

If you had done this with actual food, the answer would probably be no. The more we expose ourselves to a something, the more we get used to it. This process, known as 'habituation', applies to all sorts of things - bright lights, level of wealth and, yes, the taste of food. The first bite of chocolate is heavenly but the fifteenth usually feels less so. Now, Carey Morewedge from Carnegie Mellon University has found that people habituate to the taste of food even if they just imagine themselves eating it.

He asked 51 recruits to imagine either eating 33 M&Ms one at a time; putting 33 quarters into a laundry machine; or inserting 30 quarters and then eating 3 M&Ms. Afterwards, everyone was given a bowel bowl containing 40 grams of real M&Ms, and allowed to snack to their hearts' content. On average, Morewedge found that everyone who imagined shoving quarters ate around 4 grams of candy, while those who stuffed their imaginary faces ate around half as much.

In a similar second experiment, people who imagined eating 3 M&Ms eventually ate more of the actual sweets than those who imagined eating 33. Those who imagined putting quarters in machines ate similar amounts no matter how many hypothetical coins they used. These results all support Morewedge's idea that people only habituate to sensations after repeatedly imagining them - 33 imaginary sweets will satisfy one's candy cravings but 3 won't.

This effect is very subtle and very specific. For a start, it's not enough to imagine putting M&Ms in a bowl; you actually have to eat them. In fact, people who pictured themselves putting 30 M&Ms into a bowl actually ate more of the sweets than those who only imagined 3 of them.

Nor is it good enough to imagine eating any old type of food. If volunteers ate M&Ms in their head - even 30 of them - it didn't affect how many cheese cubes they guzzled down in real life. People only ate fewer cheese cubes if they imagined themselves eating lots of cheese cubes. This shows that the volunteers weren't just feeling a bogus sense of 'fullness' -their mental exercises were actually quelling their desire for food.

Think about eating enough of a certain food, and you don't want it as much.

Morewedge confirmed that by replaying replayed the first experiment with 80 new volunteers. This time, cheddar cubes stood in for M8Ms, while laundry quarters reprised their earlier role. Afterwards, the recruits all played a simple game where they clicked on a picture of a cheese cube for points, which would be later redeemed for actual cheese. As the game went on, it took more and more clicks to earn a single point - four at first, then eight, then sixteen and so on. They could stop the game at any point, but those who had eaten 30 mental cheese cubes gave up after fewer clicks than those who had eaten three or none. They just didn't want as much cheese.

Counter-Intuitive Explanations

Before and after the experiment, Morewedge also asked the volunteers to rate how much they liked cheddar. He found that their scores were just as high, no matter how many cubes they had imagined eating. This shows that people eat less food after a burst of imaginary eating, not because they like the morsels less, but because they simply didn't want them as much.

If these results seem counter-intuitive to you, you're not alone. Morewedge described the cheese and chocolate experiment to 80 people and asked them to predict the results. They correctly predicted that volunteers would eat fewer cheese cubes if they had imagined eating cheese. But they wrongly guessed that those who ate more cheese in their heads would eat more cheese in real life.

Their mistake is understandable. After all, previous studies have consistently found that thinking about something desirable makes people desire it, be it a cigarette or a steak. But in most of these studies, volunteers imagined a single vivid sensation - the first appetite-whetting bite of chocolate. In Morewedge's study, they went through the mental equivalent of the thirty-third duller bite.

It's another reminder that experiencing something in your mind often has the same effects as experiencing it in the flesh. Both trigger the same parts of the brain, the same emotions, and the same responses. Think about a huge spider crawling across your leg and your heart rate will probably go up, just as it would if a real spider was there. If that's the case, it stands to reason that repeatedly imagining something has the same effect as repeatedly experiencing it for real: it dulls your responses.

This has an obvious practical implication: it may be possible for people to suppress their cravings for unhealthy foods or drugs by repeatedly partaking in their vices. It's a fascinating idea, and one that deserves some further study. In the meantime, I have learned that writing about the psychology of hunger in the middle of the night brings on an unbearable case of the munchies. I'm off to imagine myself repeatedly sticking my face into a cake.

By Ed Yong
Reprinted with permission from Discover