Many dietitians point to another, more obvious reason why some diet drinkers gain weight: They use soda as justification for bad food choices. “I’ve had clients tell me that they figured it was OK to have a cheeseburger and fries because their soft drink didn’t contain calories,” says New York City-based dietitian Tanya Zuckerbrot.

Slimming solution: Whenever possible, swap your diet soda for water, unsweetened iced tea or seltzer with a splash of juice. If you can’t live without it, try to cut back to no more than one every other day – or ideally, save it as a treat, advises Zuckerbrot.

3. Too many choices.

You’d think that having lots of different types of food on your plate would make you feel more satisfied, but in fact, the opposite is true. A study at the University of Pennsylvania in Philadelphia found that people given a bowl of 300 M&Ms with 10 different colors ate 43 percent more than those given the same amount of just seven colors. “When you have fewer items, it’s easier to grasp how much you’re consuming,” says Judith Beck, PhD, clinical professor of psychology in psychiatry at the University of Pennsylvania, and author of the Complete BeckDiet for Life (Oxmoor House, 2009).

Slimming solution: Limit yourself to three or four choices when you’re eating at a salad bar or a buffet instead of taking a taste of everything, advises Dr. Beck. “It also helps to decide what types of food you’ll choose before piling your plate; for example, lean protein, a green salad and some whole grains.”

4. What’s in a name?

In a word, calories. There’s a reason restaurants give their desserts tempting names such as Molten Chocolate Lava Cake. Those luscious sounding words work.

A study from the University of Illinois found that when a piece of plain chocolate cake was given the name Black Forest Double Chocolate Cake, people said it tasted better and were more likely to buy and eat it than when it was called Chocolate Cake. Conversely, the researchers found that when foods are labeled as healthy (think “contains soy” or “low-sodium”), people assumed they wouldn’t taste as good.

Slimming solution: Be aware of this phenomenon so you’ll be less susceptible to it. “Remember that you can’t depend on the name of the product to tell you how satisfying it will be,” says dietitian Dawn Jackson Blatner of Chicago.

Remembering a time when a tempting description suckered you into ordering a dish that sounded better than it actually tasted may also provide a reality check in a moment of weakness.