From Scientific American:
Yiddish literature includes numerous stories about the mythical village of Chelm, filled with people who, well, let’s put it this way: they are not likely to graduate first in their Yeshiva class. One such tale involves befuddled carpenters who could not figure out why, no matter how many times they cut additional pieces off the ends of a board, it was still too short. Oy. Now new research shows that when it comes to food, most people are honorary citizens of Chelm. Investigator Alexander Chernev, for one, has discovered that many people believe they can cut a meal’s calorie count by an ingenious method—adding more food! Oy.
Chernev, who investigates consumer behavior at Northwestern University’s Kellogg (snap, crackle, pop) School of Management, spends an inordinate amount of time around hamburgers for a guy who’s not managing a McDonald’s. Publishing in the Journal of Consumer Psychology, he explains that people act as if healthful foods have “halos”—their healthfulness extends to the rest of the meal. Vegetables and fruit: big halos. Angel food cake: no halo. Go figure. Here is where the mind applies cockamamie calculus to meals. Eaters consider a food’s healthfulness to be related to how “fattening” it is. “Because healthier meals are perceived to be less likely to promote weight gain,” Chernev writes, “people erroneously assume that adding a healthy item to a meal decreases its potential to promote weight gain.” More is less, more or less.