There is research that has explored this situation. A great paper by Daniel Read and Barbara van Leeuwen in 1998 in Organizational Behavior and Human Decision Processes found that people who were hungry were far more likely to select tempting unhealthy food for themselves than people who were not hungry.

There is also good evidence that needing to eat can influence how much you like certain foods. In a paper that I did with Miguel Brendl and Kyungil Kim that was published in the journal Emotion in 2007, people who needed to eat found foods more attractive than people who did not need to eat. In this study, the influence of was specific to the time of day. People participating in the study in the morning rated breakfast foods (but not dinner foods) as highly attractive. People participating in the study in the evening rated dinner foods (but not breakfast foods) as highly attractive.

A paper by Remi Radel and Corentin Clement-Guillotin in the April 2012 issue of Psychological Science suggests that one reason why motivation affects the of foods is that it changes how easily we can think about foods. In their study, participants came to the lab around midday. None of them had eaten in several hours. Half of the participants were then sent to a cafeteria to eat lunch. The other half did not eat.

In the experiment, participants saw words flashed briefly (for 33 milliseconds) on a computer screen. Then, they were shown a pair of words. They were asked to give a rating of how visible the word seemed to be. Then, they were shown a pair of words and they were asked which one was the one they had seen. Some of the words were related to food (like bread or cake). Other words were unrelated to food (like boat or glove).

People’s performance on the words unrelated to food were not affected by their level of hunger. However, compared to people who had just eaten lunch, hungry people identified words more effectively and felt like the words were more visible. That is, having a need to eat made it easier for people to see words related to foods.

Let’s put all this together.

When you are hungry, your motivational system wants to help you to satisfy your need to eat. One way that it helps out by making things related to food easier to see. Once you notice those things in the world, you can take action. If you are in the grocery store, you will be likely to put those items in your cart. If you are on a buffet line, you will put them on your plate.

So, what can you do to protect yourself? Obviously, you should avoid going to the store when you are hungry. Sometimes, of course, you have to shop when hungry. In those cases, make a list before you go to the store. The list helps you to stick to the items you intended to buy rather than allowing things in the world to influence your choices.

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