This scene from Supersize me looks at how television plays a role in a child's attitude toward food.

Human beings are cognitive misers. Baumeister et al (1998) argued that making decisions actually uses energy which we would rather not use. As human beings, we tend to apply the following mantra to decision making: I don't know, I don't care and I don't have time. 

In order to eat healthy food and thereby maintain a healthy weight, I would have to know what to look for when reading the labels on food products. In addition, you have to care about healthy eating. Finally, many of us feel that we don't have time to read all the labels in the grocery store or to educate ourselves on healthy eating. That is why we use heuristics - that is, short-cuts to decision making which are often irrational in nature. Heuristics are simple procedures that help individuals find adequate, though often imperfect, answers to difficult questions.

One heuristic that seems to affect eating behaviour is the representativeness heuristic. When the children above see Ronald McDonald, they associate him with positive images. Therefore, he represents a positive lifestyle - and thus good eating. When people make rapid decisions they rely on heuristic cues, such as the appearance of objects, familiar pictures, shapes, sizes, logos, brands, and prices. This automatic decision-making mechanism allows people to function efficiently and frees up limited attention and cognitive capacity to address other demands.

Many food products use signs and symbols in their packaging that suggest a product is healthier than it really is in order to promote sales. Tversky & Kahneman have shown that the representativeness heuristic is often used to make decisions - that is, if there are cues that make it look healthy, then it must be healthy.

In his book, The Social Animal (pp 156 - 157) Elliot Aronson writes about a consumer study done on the role of heuristics in food choice. Parents were asked whether they would buy Lucky Charms (an American breakfast cereal) or Quaker's 100% Natural for their children. Parents easily chose the Quaker's 100% Natural. Both the name and the picture of fields of the wheat on the box told them that it was healthier. They had used the representativeness heuristic to make the decision, rather than doing a bit of research. 

In 1981 the magazine Consumer Reports conducted a test of breakfast cereals. Their researchers fed young rats, which have nutritional requirements very similar to humans, an exclusive diet of water and one of thirty-two brands of breakfast cereal for a period of eighteen weeks. They found that the rats grew and remained healthy on a diet of Lucky Charms. This was not the case with a diet of Quaker's 100% natural. A careful look at the ingredients shows that Lucky Charms is lower in calories and in saturated fats than 100% Natural. While it is also slightly higher in sugar, this difference is of no dietary significance. In this case, judging the cereal by its box led to a false assumption about the healthy nature of the cereal.

Visual cues can also lead to an illusory correlation, as seen in the study by Song and Schwarz (2008). In their study, they asked 20 participants (12 female, 8 male) to read instructions for a new exercise plan.  The instructions were either written in an easy-to-read or a difficult-to-read font. The participants who read the directions in the easy-to-read font estimated that the plan would be easier and more enjoyable - and that they would be more willing to try the plan, than those that read the difficult-to-read font. It seems that the participants made an illusory correlation - that is, if the text is difficult to read, then the exercise must also be difficult to do.

Another argument is that high cognitive load may impair our ability to make good decisions. Pascoe and Richman (2010) found that women who were able to recall more examples of personal discrimination - or who were given unjustified negative feedback on a task - were more likely to choose a chocolate bar over a granola bar than women who recalled fewer examples of discrimination or received fair feedback. Of course, this is done under controlled conditions and is not a longitudinal study - so, although it may give us some insight into how people make food choices, it may not necessarily explain obesity.

One of the great areas of cognitive psychology is the theory that our beliefs can affect our behaviour - and in some cases, even our physiology.  The following study by Aila Crum is an intriguing example of how our beliefs may affect the way our body processes food.

Another study of how beliefs can affect eating behaviour was carried out by Wansink, Just, & Payne (2009). In their study, 62 MBA students sat through a lecture explaining that if presented with a one-gallon bowl of Chex Mix, they would eat more than if presented with two half-gallon bowls. The rationale is that they will base their serving sizes on the size of the bowl that is offered.  Taking from a larger bowl means that they will consume more than when taking from a smaller bowl. Despite this lesson, the students who served themselves from the one-gallon bowl ate 59% more than the participants who chose from one of two half-gallon bowls. The participants did not believe the size of the serving bowls influenced their behaviour. Wansink argues that this is evidence that sample size matters.  But does it?

 Teacher only box

As part of the discussion of Wansick's work, you may want to show students this video on the problems of replicability.

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The discussion of whether the p-values matter in Wansick's case can be an interesting discussion.  The fact that he changed people's eating habits for the better is a positive outcome from poorly done research.  So, arguing that portion size matters or that we should eat more slowly is not in and of itself problematic.  However, the problem is that allowing such research to remain "published" undermines people's trust in science. It is important that scientific journals respond quickly when fraudulent data is discovered. To not do so makes it possible for people to question the validity of any scientific research - and that could undermine people's trust in public health.