Tuesday December 14 2010
Participants imagined eating M&Ms and cubes of cheese
“Imagine eating if you want to lose weight,” The Guardian has suggested. The newspaper said psychologists have found that simply imagining eating high-calorie food, such as chocolate, can reduce your appetite and help you lose weight.
The research behind this widely reported news was a set of small observational studies that compared people’s consumption of M&Ms and cheese after imagining scenarios where they had or had not eaten the foods. There was some consistency in the findings, which suggested that greater time spent imagining a food will reduce the amount eventually consumed. This pattern seemed to generally hold for both M&Ms and cheese.
While it may be attractive to think that we could reduce the amount of chocolate we eat simply by imagining eating it, it should be remembered that this was a small, experimental study. Whether the theory applies to most people outside the laboratory remains to be seen, as does the effect of this approach on health. As it stands, newspapers are oversimplifying the issue by suggest that mental imagery is a way to lose weight.
Where did the story come from?
This study was carried out by researchers from Carnegie Mellon University in Pittsburgh. The work was supported by a grant from the Berkman Faculty Development Fund at the University. It appeared in the peer-reviewed medical journal Science.
The story was covered by several papers, all of whom suggested that imagining a favourite food makes the real thing less appealing. The underlying observational evidence provided by this study is at an early stage, generating hypotheses rather than proving anything, and the media have been overly optimistic in applying the results of this study to real-life weight loss.
What kind of research was this?
This observational research investigated the theory that imagining a stimulus, such as food, would lead to “habituation”, i.e. a reduction in physiological and behavioural responses to it. The authors thought that simply thinking about food should lead people to habituate to it. They carried out five experiments to test their theory that imagining eating specific foods would affect people’s subsequent consumption of that food.
What did the research involve?
In the first study, 51 people imagined the action of eating 33 M&Ms one at a time. A similar-sized group of control subjects imagined inserting 33 coins into a laundry machine (this was thought to approximate the physical movements of eating M&Ms). For the remaining experiments, the type of imagined scenarios were varied, such as people imagining inserting 30 coins into a laundry machine followed by imagining eating three M&Ms, or vice versa.
After these scenarios, all participants were allowed to eat freely from a bowl containing 40g of M&Ms. The amount that each participant ate was recorded. The researchers then used statistical tests to compare whether there was a difference between the quantity eaten and the type of imagined scenario. Other experiments repeated the process but tested whether imagining consumption of the food would work or whether it was sufficient to imagine moving the M&Ms into a bowl.
The researchers went on to test the mechanisms behind this habituation in a fourth experiment that varied the imagined food. In this test, they asked the participants to imagine consuming cheddar cheese and investigated whether this had any effect on subsequent cheese consumption. They then compared this to a scenario in which the participants were asked to imagine eating M&Ms but were then offered cheddar cheese instead.
To test the theories they had developed earlier in their research, in their fifth experiment the researchers enrolled 80 new people and, based on what they had previously found out, tried to predict the responses of these people. They also measured the change in liking cheese by measuring consumption before and after an imagination task and by testing whether people imagining eating 30 cubes were more motivated than those who only imagined eating three during a computer game that allowed them to win points by clicking on images of cheese.
What were the basic results?
Overall, the study found that the higher the number of M&Ms participants imagined consuming, the fewer they consumed when they could. Those who imagined eating 30 M&Ms ate fewer than those who imagined eating three. In the experiments that followed, people who simply imagined moving the M&Ms ate the most M&Ms overall.
As with the M&M experiments, participants who imagined eating 30 cubes of cheddar cheese ate less cheese than those who had imagined eating only three cubes. In the groups who imagined eating M&Ms and who were offered cheese, there was no difference in consumption.
In the fifth experiment, in which the researchers attempted to validate their theories, they were able to predict that imagining M&Ms would not affect the consumption of cheese.
In contrast, their theory that participants who imagined eating 30 cubes of cheese would eat less cheese than those who imagined eating three cubes did not hold.
How did the researchers interpret the results?
The researchers concluded that their study has shown that repeatedly imagining the consumption of food leads people to habituate to it. They also said that people who imagined eating more of a food were less motivated to eat it than those who imagined eating less of it.
According to the researchers, these findings have important implications in several fields, including reducing cravings for unhealthy foods and drugs or easing phobias.
These small, observational studies are intended to be generate theories, in other words to raise some questions that larger, more robust research could try to understand in greater detail. The application of these findings to human health is, therefore, unclear.
The researchers were unable to validate all their hypotheses in the fifth experiment in a new set of people. This may suggest that different groups or individuals have different responses to imagining food. For some people, imagining food may be linked to a variable range of emotions that may mean their response is not predictable.
It is attractive to think that imagining eating chocolate will reduce actual consumption. Whether this is true for the majority of people remains to be seen, as do the effects of this approach on health. It is oversimplifying the matter to suggest that mental imagery is a way to lose weight.