Sidestep 5 big diet blunders

Fattening flub: eating a variety of foods
Why it doesn't work We're hardwired to eat more when faced with a number of different choices. This mechanism gives us a slimming advantage when a spread consists of low-cal, filling fare such as veggies and lean protein. But unless you pass by the snack aisle and plant your cart by the produce bins, chances are your fridge is filled with variety of a different sort. What does work It's OK to have a few treats in the house, but limit your stash to one or two types—the rest of your shelf space should be reserved for a range of nutritious foods. Need ideas for what to do with all those veggies, fruit and whole grains? Search our database of delicious recipes.

Fattening flub: never going for seconds
Why it doesn't work If we're held to a single serving, we want to make it count. It's human nature—get your fill while you can. The problem is, if you load up your plate with a heaping pile of food, chances are you'll eat it all, says Madelyn Fernstrom, Ph.D., director of the Weight Management Center at the University of Pittsburgh Medical Center. Knowing you can go back for another helping if need be encourages you to put less on your plate the first time around and allows your body to register fullness before the second helping. What does work Begin retraining yourself to start off with at least 20 percent less than you're used to eating. Then after 20 minutes—the time it takes for us to start to feel full—gauge your hunger. Still have an appetite? Dig in again, but keep it reasonably portioned.

Fattening flub: using exercise as an excuse to eat more
Why it doesn't work Unfortunately, exercise does not burn as many calories as we might think. Thirty minutes on the elliptical, for example, cancels out only one Reese's Peanut Butter Cup, says Ann Yelmokas McDermott, Ph.D., director of the Center for Obesity Prevention and Education at California Polytechnic State University in San Luis Obispo. If you're training for a sporting event, you may need to eat more to fuel your workouts—otherwise, consider regular exercise a keep-it-in-check tool, not a free pass to bulldoze your way through the mall food court.What does work Exercise—but not for the reasons you'd imagine. While cardio won't completely burn away a weekend binge, it does benefit health by increasing energy and lowering risk for heart disease. Another perk of busting a move? "Good behavior often begets other good behaviors," McDermott explains. Working out may make you feel good, so you eat better.

Fattening flub: hanging a tiny cocktail dress on the closet door for motivation
Why it doesn't work You may think the hopeful purchase of a little black dress or photos of thin models will encourage you to lose, but you'd be wrong. "Some women feel worse about themselves after seeing skinny models in ads. And if you feel bad about yourself, it's harder to stick to an eating and exercise plan," says Kathleen Martin Ginis, Ph.D., professor of health and exercise psychology at McMaster University in Hamilton, Ontario. What does work Focus on accomplishments, not shortcomings. "When you notice you're comparing your body to the girl next to you at the track, stop. Instead, think, I can run for five more minutes than I could a month ago," Martin Ginis says. And don't fixate on the end goal, such as the 20-pound loss. "Plan short-term goals, like 'I'm going to the gym three times this week, or I'm cooking a healthy dinner tomorrow,'" she suggests.