Fit Nation

It would be an awful lot easier count calories if we could just see the pesky things. Add up how many of them are on your plate, and you never have to eat a single one more than you want to. But calories are very good at hiding themselves—never more so than at health-food restaurants.

Almost everyone has had the experience of bypassing a McDonald's for a virtuous, diet-friendly place, only to leave feeling oddly more stuffed than if you'd just had the Big Mac and fries. That's no illusion. Menus at restaurants that market themselves as healthy alternatives are often big minefields, booby-trapped with hidden fat and calories than can blow any diet to smithereens.

Take those heart-healthy symbols that keep popping up next to menu offerings. A 2003 study in the Journal of Marketing found that diners may trust the little icons more than their own common sense, believing that there's a reduced risk for heart disease even if the symbol is next to a manifestly fatty food like lasagna. We're also suckers for the term low cholesterol, thinking that it's synonymous with low fat, which is by no means always the case.

Even when we make the right choice, we manage to trip ourselves up. If we're having a healthy entrée, we decide we might as well cut loose with the extras, adding a helping of mashed potatoes to the lean piece of fish or loading up a salad with cheese or croutons or too much dressing. Healthy snacks can be similarly fraught. One study showed that if you give people the low-fat, low-calorie version of a food like a granola bar or Chex Mix, they'll compensate by eating 28% more of it than they would of the higher-fat version. In another study, people were given sandwiches that they were told came from either McDonald's or Subway, which has successfully marketed itself as a smarter alternative (even if its meals can still be stuffed with calories). The subjects eating the food labeled Subway often washed it down with sugary soda or followed it up with cookies or chips, apparently concluding they had a little room to indulge.

Perhaps worst of all, there's the notorious what-the-hell effect. Calorie counters who realize they're exceeding their limit, even in a health-food restaurant, often don't pull back to contain the damage but reason that the day is a loss anyway, so they might as well have fun, piling on desserts and sides they'd otherwise avoid.

Such a combination of rationalization and misinformation is hard to overcome, but there are things we can do. First, keep alternative options in mind. A 2005 study showed that people are actually more likely to choose a lower-fat cheesecake when it appears on a menu alongside a high-fat version, almost as if picturing that dense serving of after-dinner indulgence makes the lighter choice more appealing. Having a real sense of serving size and calorie content can help too. Most studies suggest that only 10% to 20% of people really know how to count calories. When the rest of us bother to guess, we usually lowball what's in a meal by as much as 45%. One solution even for the least calorie-savvy is to order what you want but push your plate away while you've still got a sizable portion left. If you have to ask the waiter to clear the plate so you're not tempted to dig back in, do so.

Finally, don't be too pure. There's nothing that makes food harder to resist than being told you can never have it. The occasional, moderate-size serving of warm chocolate cake or McDonald's fries is not going to kill you. And in case you forgot, it will be utterly delicious.

Sanjay Gupta's Fit Nation series airs on House Call on CNN, Saturdays and Sundays, at 8:30 a.m. E.T.

—With reporting by Shahreen Abedin