Thinking About Eating May Mean Eating Less

Carey Morewedge, assistant professor of social and decision sciences, Carnegie Mellon University, Pittsburgh, Pa.

Researchers at Carnegie Mellon University say that repeatedly thinking about eating a certain food — M&Ms or cheese — led study participants to eat less of the food once it was presented to them. Researcher Carey Morewedge describes the work and its implications for dieters.

Copyright © 2010 NPR. For personal, noncommercial use only. See Terms of Use. For other uses, prior permission required.

IRA FLATOW, host:

This is SCIENCE FRIDAY. I'm Ira Flatow. Roasted turkey with chestnut stuffing, mashed potatoes with homemade gravy, sugar cookies and hot chocolate with whipped cream. Am I making you hungry? What if I say doughnuts for Homer Simpson? Yeah.

You already know that thinking about food can whet your appetite. I'll be your salivating right now. But did you know that you can also think your way into being satisfied? Using M&Ms and cheese cubes, researchers at Carnegie Mellon discovered that by imagining eating a lot of something, your mind subconsciously limits what you later put into your mouth.

Joining me now to talk more about it is Carey Morewedge. He is assistant professor of social and decision sciences at Carnegie Mellon University in Pittsburgh, Pennsylvania. Here from that sidewalk is - welcome to SCIENCE FRIDAY.

Professor CAREY MOREWEDGE (Assistant Professor of Social and Decision Sciences, Carnegie Mellon University): Thanks for having me.

FLATOW: Tell us about this experiment, your study, where you had people imagining they were actually eating something?

Prof. MOREWEDGE: Right, so let me walk you through what persons experienced. So imagine you're participating in an experiment. You come to the basement in Carnegie Mellon University.

FLATOW: Right.

Prof. MOREWEDGE: You would be - you'd walk into our laboratory, where you'd see a number of computers in different cubicles, and you would be sat down and maybe told that you're going to participate in an experiment on imagination and perception. We told people this because we didn't want them to know that we were going to measure their eating.

So what would happen next is you'd be asked to imagine performing a number of repetitive tasks, and then you'd be asked to estimate the size of the things that you imagined, and then afterwards we gave people some food to eat.

And what we manipulated was whether people imagined eating three or 30 units of a food such as M&Ms or cheddar cheese cubes, or people imagined eating a different food or moving the food or doing something...

FLATOW: So those were really the controls, but they didn't know they were...

Prof. MOREWEDGE: Exactly.

FLATOW: But the real idea was to see if they imagined eating that food first, if they would eat less of the food.

Prof. MOREWEDGE: Right, and so we found that people who imagined eating 30 M&Ms instead of three, or 30 cheese cubes instead of three, afterward ate less from a bowl containing 40 grams of cheese cubes or M&Ms, and in this case it seemed that only imagining the consumption of the specific food reduced their actual consumption later on.

FLATOW: Did it have to be the consumption of the same food?

Prof. MOREWEDGE: Right, so in one study we had participants imagine eating three or 30 cheese cubes, or imagine eating three or 30 M&Ms, and then we gave them a bowl filled with 40 grams of cheddar cheese. And there we found only people who imagined eating cheese were affected by this induction.

So when people imagined eating M&Ms, it didn't matter whether they ate -or imagined eating three or 30, they showed no difference.

FLATOW: Did they have to actually think about the food in their mouths when they were doing this?

Prof. MOREWEDGE: Well, we didn't instruct participants to imagine chewing, biting or swallowing. But we did do one study that may address your question.

So in this study we had - we were worried that maybe people just thinking about food more generally might lead people to reduce their consumption. Maybe you just feel full, or maybe you're disgusted by the thought of the 30th M&M when you see it on the screen.

FLATOW: Not me.

(Soundbite of laughter)

Prof. MOREWEDGE: Or maybe you're just bored. So in these cases, what we wanted to do was we tested - we compared people who imagined eating three M&Ms or 30 M&Ms versus people who imagined moving three M&Ms or 30 M&Ms into a bowl. And what we found there was that when people imagined eating 30 M&Ms, they ate fewer M&Ms than people who imagined eating three.

But when people imagined moving M&Ms, we found the opposite effect. So people who imagined moving M&Ms, who imagined moving 30, ate more M&Ms than people who imagined eating three.

FLATOW: So really it was the imagining of the eating process that was important here. And why do you think that is? What is going on in our minds, that just the imagining of it...

Prof. MOREWEDGE: Well, that's a great question. So we think what the imagining consumption is doing is leading people to habituate to a food. And what I mean by habituation is it's a basic process that we see towards light, towards income, towards all these different kinds of stimuli, and it's basically people become less responsive to anything that they're exposed to repeatedly.

So for example, the 10th bite of pancake is much less desirable than the first. Or when you walk into a room, a really bright light might blind you at first, but then your eyes adapt to it.

FLATOW: Do you think this has practical values if you want to eat less? Or could you extend it to other things we do, like if you want to get rid of - if you want to stop smoking, can you imagine you had smoked a cigarette and not...

Prof. MOREWEDGE: Well, that's a great question. We certainly think that it should extend to other kinds of stimuli. With the extent to smoking, addictive substances have a lot more complex kinds of psychological dynamics, and we don't really necessarily know whether it will extend to that. So it tells smokers to avoid trying this because we don't want to get them even more addicted.

(Soundbite of laughter)

Prof. MOREWEDGE: But with regards to food, I think there's a few things that we want to test out first before we recommend this as a dieting technique. But it's certainly giving us some more insight into the kinds of things that make people stop eating unhealthy foods and might help them lead to make healthier food choices.

FLATOW: But what is there about - you know, we always heard that when you eat something, you feel sated because your stomach expands and things like that. So are we getting in a phony signal to our food-eating centers or something like that?

Prof. MOREWEDGE: Oh, that's a great question. So a lot of - the problem with relying on your sort of feeling of fullness is that it sort of unfolds much more slowly than your idea of sort of when you should stop eating.

And there's been a lot of psychologists and food scientists and behavioral economists who have been doing a lot of research lately, looking at the psychological processes that lead people to infer when they should stop eating.

So people - everything from Brian Vonsink(ph) at Cornell, for example, had looked at some really interesting work on how different cues in our environment can lead us to feel like we should begin or end a meal. So...

FLATOW: Is that the famous soup plate, the soup bowl, the unending soup bowl experiment?

Prof. MOREWEDGE: Right. So he's got this - he had people come into the laboratory and there's - you'd sit in front of a soup bowl, and he basically has it secretly hooked up to a five-gallon jug. And as you're eating, it never goes down. So...

FLATOW: People continue to eat it, right?

Prof. MOREWEDGE: Right. I think they eat about three times as much soup as people who have normal bowls.

FLATOW: So they're looking for that visual cue.

Prof. MOREWEDGE: So in this case they're looking, right, they're looking for a visual cue, or if he manipulates the size of the plates - and there are other people who have been doing great work too, like Paul Rozin(ph). He's a psychologist over at the University of Pennsylvania, and he has - he brings amnesiacs into the laboratory. And he gives them lunch, and then he says thank you, cleans up, leaves the laboratory, and then comes back in a few minutes later, once they've forgotten about their meal, and then gives them lunch, and they eat it, and then he leaves the room and repeats this process.

And he finds that they tend to eat about two and a half meals, whereas people with their normal memory would not.

So there's - people have been looking at this question from a lot of different perspectives. What's really exciting about this new research is that it's the first to show that just pure psychological processes can start this sort of process, whereas in other cases people were both exposed to the food that they imagined eating, and people manipulated psychological processes. This research is really sort of showing us that just thinking alone can start these kinds of processes.

FLATOW: Now, I'm tempted to say the placebo food effect on this sort of thing.

Prof. MOREWEDGE: Right, I mean...

FLATOW: Could that be something like that involved, some sort of placebo effect when you're thinking about eating, and you say, well, I've already eaten?

Prof. MOREWEDGE: That's a good question. And it would be interesting to see sort of what - how this kind of research more generally could apply to placebo effects. But we do find that there's been a lot of research in neuroscience that has been mapping the connections between mental representations or thoughts of an event and the actual experience.

FLATOW: Right.

Prof. MOREWEDGE: And there does seem to be a lot of overlap. So for example, if you think about a spider crawling across your leg, it's going to - you're going to find the same increase in heart rate and perspiration that you would if you were in the presence of an actual spider.

And the most fascinating of these effects are mental practice effects. So sometimes people practice motor tasks, and then when you find that people mentally rehearse these tasks, their performance seems to improve.

FLATOW: Yeah, the envision how to be a better baseball player, tennis player, something like that. They envision the moves they're going to be doing.

Prof. MOREWEDGE: Right, and this suggests that the same kinds of thoughts that we have about eating seem to be eliciting similar kinds of responses as actually eating itself.

FLATOW: In this day of brain scans and things, can you actually watch that now happen in the brain, if somebody's not eating but thinking about it and see where all the connections are going?

Prof. MOREWEDGE: Well, I'm not a neuroscientist. I'm a psychologist by training. But I'm certain that we could look at sort of what kinds of brain areas are involved in this process, and it would be really exciting to do so.

FLATOW: But you're going to try to continue to measure psychological responses.

Prof. MOREWEDGE: Right, so we have a couple of grants out right now where we're trying to look at sort of physiological effects of this kind of induction on salivation and other kinds of questions.

FLATOW: Well, there's the oldest one in the book, right, salivation, Pavlov?

Prof. MOREWEDGE: Yeah.

FLATOW: There was no food, but they were still salivating, the dog.

Prof. MOREWEDGE: Yeah, exactly.

FLATOW: So this is very - so this is somewhere really hardwired into us someplace, you think.

Prof. MOREWEDGE: Well, the overlap between experience and our direct sensation seems to be quite - there seems to be a lot of overlap there. And it's an exciting new area that a lot of psychologists are exploring right now. It's certainly a hot topic of research.

FLATOW: Let's see if we can get a phone call or two in here. Let's go to John in Anchorage. Hi, John.

JOHN (Caller): Hi, Ira.

FLATOW: Hi there.

JOHN: I have a question. I think a couple years ago you had a guest on who had done a study where instead of eating chocolate, you just envisioned it, right? And you still had some of the same weight gain because it triggered chemical responses in the body. So without the benefit of eating, you actually suffered some of the consequences.

If that's right, do you get some of the same thing from envisioning eating the M&Ms, eating fewer of them, that you still get some of the same body responses?

FLATOW: Thanks for the question, John.

Prof. MOREWEDGE: Well, that's a great question. So we didn't weigh our -certainly didn't weigh our subjects before and after the experiment. So I can't answer your direct question in terms of that. But it would be interesting to look at sort of what are the long-term responses to these kinds of simulations.

Certainly people who have phobias, even though that they don't necessarily encounter the things that they fear, their thoughts of the feared stimulus can affect their stress levels and their cortisol. So it's possible that there are long-term physiological effects to just thinking about food as well, but...

FLATOW: So there must be a product somewhere down the line in this sort of thing that you can - maybe a weight-loss product.

Prof. MOREWEDGE: Well, my colleagues and I had a joke that if we ever had a diet book, it would be a flip-book, and you'd go to the page for the to the chapter for the food that you were craving eating.

But to be serious, we really don't know how long this effect will last. And one of the problems with using habituation as a dieting strategy would be that people also show dishabituation. So if you give people something other than the thing that they've been habituated to, then it seems to undo the process.

FLATOW: Well, what about hypnosis? Could you give a hypnotic suggestion that when you look at a certain food, you feel like you've already eaten it?

Prof. MOREWEDGE: I can't answer that question. But it's a possibility.

FLATOW: But there hasn't been any research in that that you know about?

Prof. MOREWEDGE: Well, there's been research, I know, that looks at inducing hypnotic disgust, and that can influence people's judgments about how immoral or moral a behavior has - seems to them, because it provokes a feeling of disgust. But it's hard to say. There hasn't been a lot of good hypnosis research in this area.

FLATOW: Well, it certainly looks like there's food for thought here.

Prof. MOREWEDGE: Definitely.

FLATOW: Carey, thank you for taking time to be with us. And we'll be right back. Carey Morewedge is assistant professor of social and decision sciences at Carnegie Mellon University in Pittsburgh. Good luck to you.

Prof. MOREWEDGE: Thank you.

Copyright © 2010 NPR. All rights reserved. No quotes from the materials contained herein may be used in any media without attribution to NPR. This transcript is provided for personal, noncommercial use only, pursuant to our Terms of Use. Any other use requires NPR's prior permission. Visit our permissions page for further information.

NPR transcripts are created on a rush deadline by a contractor for NPR, and accuracy and availability may vary. This text may not be in its final form and may be updated or revised in the future. Please be aware that the authoritative record of NPR's programming is the audio.

Comments

 

Please keep your community civil. All comments must follow the NPR.org Community rules and terms of use, and will be moderated prior to posting. NPR reserves the right to use the comments we receive, in whole or in part, and to use the commenter's name and location, in any medium. See also the Terms of Use, Privacy Policy and Community FAQ.