A recent article over at NPR briefly covered the topic of food, or rather, how your body changes the way it responds based on your assumptions about the food you consume. In the article, the author points out a recent study that looked at the levels of Ghrelin (a hormone related to how hungry you feel) and how diet versions of food predictably leave your levels of ghrelin relatively unaffected, leaving you just as hungry. Sucking down a fatty milkshake, however, lowers Ghrelin levels drastically, as expected.
But there was a catch to this study. The participants drank the same drink. One was simply labeled "Fat Free - Low Calorie," while the other was labeled "Indulgent." The research and the article elude to the idea that the brain's perception of what it is consuming directly impacts the biological response to the food.