What Works: Boost Protein
Protein can take about 4 hours to digest, while carbs take only 2; slower digestion means you feel fuller longer. Plus, protein may help jack up your metabolism: In a new study from Purdue University, dieters who ate 30% of their calories from protein preserved more lean body mass while losing weight than those who ate only 18%. The more lean body mass you hold on to, the more calories you burn at rest.

Do It Your Way
Forget the cheese and bacon of diets past; instead, add a little protein to every meal and snack

Choose healthy sources

That means proteins with unsaturated fats (like salmon and soy), not the cholesterol-boosting saturated kind (packed into fatty cuts of beef and whole dairy products).

Stick to proper serving sizes
Three ounces of lean meat looks like a deck of cards, the same amount of fish is the size of a checkbook, and your thumb marks an ounce of cheese.

Add protein to your favorites
Combine ground turkey or shrimp with spaghetti and sauce; stir 1 ounce of walnuts into oatmeal; spread a little almond butter on toast before the jam.

What Works: Replace Meals with Bars and Shakes
These products make portion control a snap. "It's calorie cutting without a calculator," says Nonas. An analysis of studies from Columbia University found that women who had one to two liquid meal replacements daily lost an extra 2 pounds per month compared with other dieters who had the same calories.

Do It Your Way
Think of a bar or shake as your go-to food when you're in a pinch. Whether you use them as a meal or as a snack, look for at least 3 g of fiber, 10 g of protein, and 3 g or less saturated fat, and follow these healthy eating guidelines:

As a meal: Most bars and shakes have about 220 calories, so pair either with a small salad with low-fat dressing or a piece of fruit to help fill you up.

As a snack: Between meals, 220 calories is too much. If you have a bar late in the afternoon, for example, cut dinner by half to keep your calorie counts in check.