James O. Hill, PhD, cofounder of the National Weight Control Registry

Quick Fix: Drink lunch. Eat low-fat, portion-controlled breakfasts and dinners, but use a commercial meal-replacement drink for lunch to provide an instant calorie cut.

Long-term Goal: To get moving and to work toward a regular fitness program. Try walking, doing push-ups and sit-ups at home, and grabbing a couple of soup cans for arm exercises. Every step helps.

Steven Heymsfield, MD, deputy director of the Obesity Research Center at St. Luke's Roosevelt Hospital in New York City

Quick Fix: Track and total your food intake for a week, then cut out 500 to 1,000 calories a day (500 will give you a one-pound-per-week loss). "This is easiest to do with portion-controlled meals, like frozen or liquid ones," says Heymsfield. Avoiding sugar and white flour will encourage fluid loss, which naturally occurs in the first two weeks of any diet. Water weight or not, the extra drop on the scale will get you psyched.

Long-term Goal: To become more aware of the calories you're taking in, so that eating the right amount for weight maintenance is automatic.

John Foreyt, PhD, director of the Behavioral Medicine Research Center at Baylor College of Medicine in Houston

Quick Fix: Eat 220-calorie breakfasts and lunches—a container of yogurt, a serving-size box of cereal, any food (preferably nutritious) whose label identifies exactly how many calories it contains. Then have a salad and small chicken or fish entrée for dinner. "It might get boring, but you're not going to hurt yourself with any plan that lasts just two weeks," says Foreyt, "and you'll see five or six pounds come off."

Long-term Goal: To segue into a controlled eating plan that has no snacks—which will seem luxurious after your 1,000-calorie-a-day boot camp.

Are all calories equal? Is breakfast a must? Are carbs the enemy? Wonder no more with this Q & A.