Can it? Really? I envision hoards of frightened dieters, or Twiggy wannabes, throwing away their 'Zero' cans in fear. Truth is - it can. It may. But only if you let it.

Effective weight watching, you see, begins in our heads. Then again, not all weight watching is effective.

Decision scientist Alex Chernev of Northwestern University has taken upon himself to examine what goes on in our heads (and in our tummies) when we diet. Turns out that even the smart and the savvy make dieting mistakes, and Chernev lists seven of them in 'The Dieter's Paradox' with its intimidating sub-title: "Why dieting makes us fat'. What Dan Ariely has done to our understanding of social phenomena, Alex Chernev does to our understanding of diet.

In this enjoyably illuminating book, Alex Chernev points our heads in the right direction. Using vivid insights drawn from decision science, he offers a comprehensive view of the many cues on which we base our food and dieting choices and why they sometimes lead us far astray. The Dieter's Paradox is a must-read for anyone who has tried to manage their weight and does not understand why they failed, and for anyone who has succeeded and wants to know what they're doing right.

But back to the soda.

Dieters are people, and, as such, are driven by emotion and impression more than by calculation. Thus, when adding a healthy or calorie free option to the menu, we engage in a simplistic kind of math, telling ourselves that minus (the soda) and plus (the cheeseburger) are less than if it was just the plus. Right? So wrong, but so common. In a series of experiments Chernev has demonstrated that people who added a healthy option to their meal, say, a salad, now considered its caloric value to be lower than before. He's not advocating that you ditch the salad, only that you realize that it adds, rather than subtracts, calories. Nor is he suggesting that you drink sugary beverages - just don't mistake the zero cal ones for being slimming.

Another common error highlights how impressionable we are when determining caloric value. When presented with a cake, people estimated it to contain considerably fewer calories if - and this is a real mind blower - there's a carrot painted on the frosting. You heard me. The carrot brings about images of health and leanness, which obviously means the cake now has all of these qualities. In the eater's mind. Funny? Not if you're trying to gauge how much you should eat.

As with any bias, it also works with experts. That is, teaching about biases, researching, and even writing about them, does not make one immune. When Alex and I attended Yale's Consumer Insight conference last year, we were about to take our plates out and have lunch on the lawn, when I noticed that all he took was a small sandwich. Being a Jewish mother, I could not help but peek at the poor man's plate (no matter if he's 6 foot tall and around my age), and see to it that he would not starve. "Just one sandwich you're having?" I asked, ommitting the "oi" which would have fit right in. Dutifully he looked down at his paper plate, deduced that the bun with mozzarella wasn't going to be sufficient, and went to replenish. Three quasi-calculations took place here: Alex's initial one (one bun is enough), mine (one bun is not enough), and his second one, following mine (one bun really is not enough). But they were only quasi-calculations, not real ones, because none of them was based on an accurate estimate of how many calories the bun contained, and how many he needed for the day. Even with us being scientists, we are, first and foremost, impressionable people. Which means that if Alex was holding a bottle of water rather than juice, he may have gone for 2 additional sandwiches insted of just one.

Even after reading The Dieter's Paradoxm you can still add a diet anything from the soda fountain to your 650 calories burger. But you will not longer think this sacrifice entitles you to a double fudge Sundae.

For more common mistakes see

About the Author

Talya Miron-Shatz, Ph.D.

Talya Miron-Shatz, Ph.D., is CEO of CureMyWay, and Associate Professor, founder of the Center for Medical Decision Making, Ono Academic College

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