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.

He had more than 900 subjects look at four different meals and estimate their calorie contents. The meals were a hamburger, a bacon-and-cheese waffle sandwich, chili with beef and a meatball-pepperoni cheesesteak—none of which are going to win any prizes from the American Heart Association, and all of which sound really good right now.

(I just remembered there’s leftover pizza in the fridge. Back in a mo.)

Where were we? Right, bad foods, bad. Half of the participants were also shown an obviously healthful side dish, such as three sticks of celery. Of course, the only real reason for anyone to want three celery sticks is to make an “A” that Hester Prynne could have worn on the planet Krypton or to do a surprisingly good impression of a walrus leading an orchestra. But I digress while I digest.

The subjects who saw only the main meal guessed it had, on average, 691 calories. Subjects who saw the same meal served with the perfunctory celery sticks or other healthful window dressings guessed that the entire meal had just 648 calories. That’s 43 fewer calories, which a really imaginative person could then add to the burger-and-celery-meal with, say, a cookie to get the calorie count back up to the burger by itself.

This kind of fatatouille reasoning was on display in a study that Cornell University’s Brian Wansink, a leader in eating-behavior research, presented at the Association for Consumer Research con­ference this past October. He found that people who ate at restaurants that claimed to be healthy estimated a meal’s calorie count to be only 56 percent of its true number. Individuals making this big error then compounded it by figuring their assumed low-cal meal made it okay to have more of the bad stuff, such as fries or cookies. That kind of logic will go straight to your hips.

Back to Chernev. His truly devilish discovery, which he dubs the “dieter’s paradox,” is that the strength of the belief about adding good foods to fight bad ones correlates with concern over putting on pounds: the people who worry most about their weight thought that, on average, the burger-plus-veggie combo had 96 fewer calories than the burger alone. The folks who were not anxious about adipose still fell for the halo-induced paradox, but they thought the veggies cut only 26 calories off the meal.

For public health advocates, the takeout or, rather, take-home message is that merely promoting the consumption of healthful foods may actually be calorie counterproductive. Because an apple a day keeps the paradox in play.