Field of Science

Thinking about your soul makes you want to eat junk food

Mind-body dualism is the belief that the mind and the body are separate - usually, that the mind can exist independently of the body. This kind of thinking is quite common among the religious, of course.

But what are the implications, from a psychological perspective, of a belief that mind and body are independent? That's what Matthias Forstmann and colleagues, at the University of Cologne in Germany, wanted to discover.

They ran some studies in which they implanted thoughts about mind-body dualism or about 'physicalism' (i.e. the idea that mind and body are closely connected). For example, in one study they asked their subjects to read a passage that, they said, was from a textbook they wanted them to review.

The textbook passage on dualism concluded that "In sum, the term ‘mind-body dualism’ describes the proposition that a person’s mind and body are two distinct entities." The passage on physicalism concluded, "In sum, the term ‘physicalism’ describes the proposition that a person’s mind and body are both rooted in the same physical substances."

When they later asked the students about their attitudes to a range of health behaviours (eating, exercise, hygiene, and going to the doctor's for checkups), they found that those who had been given the dualism passage were significantly less health conscious.

In another study, the subjects were offered a cookbook of their choice as compensation for completing the survey. Those primed with dualism were more likely to choose books on barbecuing or desserts, rather than the books on vegetarian and organic food.

A third study took this to another level. This time, university students were primed either with dualism or physicalism. They were then given some filler tasks, and then told to come back to the lab after lunch to get the results.

Bizarrely enough, those students who had been primed with dualism ate a lunch that was significantly less healthy than students primed with physicalism (by about 1 point on an arbitrary 9-point scale)!

Even more extraordinary is that this effect appears to work both ways. When subjects in another study were shown pictures of unhealthy food, they later reported holding significantly stronger dualistic beliefs than those shown pictures of healthy food.

Forstmann thinks that this is because people are less concerned about taking care of their bodies if they think that their minds exist independently. But they also suspect that dualism might be a defensive response to threat.

So, when shown pictures of unhealthy food, we are reminded of our limited lifespan - and react by believing more strongly in the soul!
Forstmann M, Burgmer P, & Mussweiler T (2012). "The Mind Is Willing, but the Flesh Is Weak": The Effects of Mind-Body Dualism on Health Behavior. Psychological science PMID: 22972908

Creative Commons License This article by Tom Rees was first published on Epiphenom. It is licensed under Creative Commons.


  1. The really scary part is the apparent ease with which our opinions are affected by irrelevancies.

    McD should look into sponsoring churches.

  2. I am beginning to wonder if some of the more committed religionists are actually physically addicted to "ego stroke" rewards. I have noticed that the more extreme among them exhibit a strong tendency to frequently and repeatedly seek out information that confirms their prejudices and carefully avoid information that refutes them, much like a heroin addict seeks out a fix. It is a long-term, ongoing behavior that seems to be independent of momentary priorities. I find the same to be true of far-right conservatives, whom I often see watching Fox News or listening to Rush Limbaugh continuously, all day long. Has anyone looked at this?

  3. Scott, not as far as I know. Atheists, in the USA at least, tend to be nonconformist. But nonconformists are also attracted to echo chambers that reinforce their own views - at least, that's my take on all the online fora I see. But I don't know of any studies that have actually tested that.

  4. Priming studies are so interesting, there is always some logic to it, but it often sounds unbelievable at the same time. On one hand, the idea that believing in mind/body dualism would make a person less careful about their body makes sense, if my mind lives on forever but my body doesn't, maybe it's not important to take such good care of my body. On the other hand, it seems somewhat unbelievable that someone might choose a less healthy lunch simply because they read a passage that mentioned mind/body dualism right before they went to eat. I'm so torn.

    The fact that there are 3 studies about this does help, although I also wonder how many more studies are out there that didn't give positive results and therefore didn't get published. Again, torn.

    Do you happen to know how many subjects each of these studies had?

  5. Actually, all of these studies were quite small - 30-60 subjects in each. They did come from a wide variety of backgrounds, though. Three studies were taken from a general-purpose registry of people signed up to participate in these kinds of studies, and one study recruited people from Amazon's Mechanical Turk.


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