This idea is based on a common phenomenon called “habituation”. This is when food becomes less desirable the more you eat it. For example, how the first bite of something is always better than, say, the tenth. Researchers are finding out that this process happens in your mind. So is you trick your mind into thinking that you are already eating, you will feel less of a desire to eat! Participants in a study imagined they were eating M&Ms before being presented with actual M&Ms to eat. The ones who imagined eating 30 before they actually ate, actually ate fewer M&Ms than the ones who imagined eating 3 or none at all. In order for this to work, you have to imagine eating the food that you are actually about to eat. If you imagine eating chocolate, your desire for chocolate will go down, but not your desire for eating cheese. Also, you can’t simply imagine the look, smell and smell of the food; this will actually make you more desiring of the food. You have to imagine the physical process of putting it in your mouth, chewing it, and swallowing it. More information on this study in National Geographic.