Jun 16 2009

Heuristics and Weight Gain

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I am often told by people who are frustrated at their inability to lose weight that they are not overeating. They insist that their caloric intake is low, which for most unsuccessful dieters is implausible (barring some medical condition). New research suggests that they may be sincere, but just suffering from a misleading heuristic.

A heuristic is a mental short cut – a down a dirty estimate or rule of thumb that we use subconsciously to quickly arrive at a conclusion that is mostly true. The presumed evolutionary advantage of heuristics is that they enable us to think and react quickly. A heuristic is a mental trade off of accuracy for speed.

An example of a common heuristic is the availability heuristic. Whenever we encounter a novel situation we reach for an available example from our own experience. We then assume that the available example is representative and will inform us about the novel situation.  When shopping for a dog, for example, and considering a doberman, one might observe – “my cousin had a doberman, and he was a mean and nasty dog.” This is the available example – and we will tend to make our decision based upon this one available example, without considering that it may not be representative.

Psychologists at the University of Pennsylvania have identified another heuristic that may contribute to unintended weight gain – unit bias. They found that people tend to ignore critical dimensions when considering the size of objects.

For example, they had subjects estimate the weight of different women based upon visual inspection, from either pictures or in person. The subjects were given information about the height of the women whose weight they were to guess – sometimes accurate, sometimes not. The researchers found that the subjects estimated weight based entirely on girth, and ignored height.

Likewise, the subjects were asked to estimate the amount of calories in a meal. The research suggests that the subjects did not consider portion size in their estimates. They considered only the “units” – let’s see, peas, chicken, and rice. This could mean that as portion sizes have risen in the US people have not taken this into consideration when estimating their caloric intake. They are still eating the same number of meals with the same number of components, given them the false sense that the caloric intake is the same.

Knowledge of heuristics is extremely important to critical thinking and skepticism. The more we understand about how the mind works, the more we will be able to avoid its pitfalls.

This research suggests that people should make a conscious effort to think about all relevant dimensions when estimating amounts. With regard to weight control – this means paying more attention to portions. It is already part of conventional wisdom that portion control is key to controlling caloric intake. This research supports that conclusion, and further explains why people seem to be so bad at estimating how many calories they intake.

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