Eating too much

Whether you're filling your plate with low-fat, low-carb, or even healthy, nutritionally balanced foods, overestimating how much food your body needs is among the most common mistakes, experts say.

"Many people believe they should feel not just satisfied after a meal, but stuffed," says Heller. "I think many of us have lost touch with the sensation of having had enough food."

Adds Taub-Dix: "People also tend to believe that they can eat larger portions if all the food on their plate meets the guidelines of their current diet -- such as low-carb or low-fat -- and that, of course, is also not true."

The solution: Remain conscious of portion sizes. Weigh and measure standard portions, at least at first, so you'll know what the amounts should look like. And, says Brandeis, "never use restaurant portions as your guide -- they super-size everything."