Feel full on fewer calories. It sounds like a diet gimmick. But in reality, the concept of energy density can indeed help you feel satisfied with fewer calories. By consuming fewer calories, you can lose weight over time and keep it off long-term.

To achieve and maintain a healthy weight, you have to follow an eating plan you can live with for a lifetime. That means no severe restrictions, no extreme hunger and no fads. Find out how choosing foods that are less energy dense — meaning you get a larger portion size with a fewer number of calories — can help you lose weight and control your hunger.

All foods have a certain number of calories within a given amount (volume). Some foods, such as desserts, candies and processed foods, are high in energy density. This means that a small volume of that food has a large number of calories. For example, just a half cup of mixed nuts has 438 calories.

Alternatively, some foods — such as vegetables and fruit — have low energy density. These foods provide a larger portion size with a fewer number of calories. For example, in that same half-cup serving, raw broccoli has just 15 calories, and a half cup of cubed cantaloupe has 28 calories.

Two factors play an important role in what makes food less calorie-packed and more filling:

• Water. Many fruits and vegetables are high in water, which provides volume but not calories. Grapefruit, for example, is about 90 percent water and has just 39 calories in a half-fruit serving. Carrots are about 88 percent water and have only 52 calories in 1 cup.
• Fiber. High-fiber foods — such as vegetables, fruits and whole grains — not only provide volume, but also take longer to digest, making you feel full longer.

Changing lifestyle habits is never easy and creating an eating plan using this concept is no exception. The first step is knowing which foods are best.

• Vegetables. Most vegetables — salad greens, asparagus, green beans, broccoli and zucchini, for example — are low in calories but high in volume. Each vegetable serving is about 25 calories, and typical serving sizes are 1 cup raw, a half cup cooked or 2 cups leafy vegetables. Some vegetables are starchy — such as corn, potatoes, sweet potatoes and winter squash — and contain more calories, about 70 calories in a half-cup serving.
• Fruits. Practically all types of fruit fit into a healthy diet. But some fruits are better choices than others are. Whole fresh, frozen and canned fruit without added sugar have about 60 calories a serving. Unlike fruit juices and dried fruits, these types of fruit are higher in bulk because of water and fiber and are your best choices. A typical serving is a small- or medium-sized piece of fresh fruit or a half cup of sliced fruit.
• Carbohydrates. Most foods in this group are either grains or are made from grains, such as cereal, rice, bread and pasta. The best type is whole grains because they're higher in fiber and other important nutrients. Whole grain means the bran and germ are left on the grain when it's processed. Examples include whole-wheat bread, whole-wheat pasta, oatmeal, brown rice and whole-grain cereal. Each serving of carbohydrate has about 70 calories. A typical serving is a half cup of grain, such as rice, pasta, barley or cereal, or one slice of bread.
• Protein/dairy. This includes foods from both plant and animal sources. The best choices are those that are high in protein but low in fat and calories, such as legumes — beans, peas and lentils, which are also good sources of fiber — fish, skinned white-meat poultry, fat-free dairy products and egg whites. Foods in the protein/dairy group have about 110 calories a serving, which is about a half cup of legumes, 3 ounces of chicken or fish, or 1 cup of skim milk. Serving sizes vary depending on the type of food.

Eat sweets and high-fat foods in moderation since many of these foods are high in calories but low in volume. For example, just 1 tablespoon of butter has about 100 calories and 1/2 cup M&M's has about 512 calories.

Food Group and Serving Size List (PDF file requiring Adobe Reader)

Starting a healthy diet that emphasizes fresh fruits and vegetables and whole grains makes room in your diet for some of your favorite foods in small quantities: a piece of chocolate cake or a small scoop of ice cream, for example. When you're not feeling desperately hungry and deprived, as you might on some diets, you can enjoy a small portion of dessert without guilt.

Here are ideas to make this eating plan work for you:

• Increase the ratio of fruits and vegetables in your meals. For example, add blueberries to your cereal in the morning. Or top your pasta with sauteed vegetables and tomato sauce. Decrease the meat portion on your plate and increase the serving size of vegetables.
• Experiment with new foods and combinations. Try mango or peach slices on whole-wheat toast with a little peanut butter and honey. Toss some mandarin orange and peach slices into a salad. You may find some new tastes you love that fit within your eating plan.
• Start with soup or salad. Begin lunch or dinner with a broth-based, vegetable-filled soup, or a large salad with a small amount of low-fat or fat-free dressing. These foods take longer to eat and curb your hunger. Next, serve whole grains, an extra portion or two of vegetables and a small serving of lean protein for your main course. By the time you get to dessert, you may not even have room for that cup of mixed berries topped with a spoonful of vanilla yogurt or low-fat ice cream.

By eating larger portions of foods less packed with calories, you squelch those hunger pangs, take in fewer calories and feel better about your meal, which contributes to how satisfied you feel overall. So go ahead and have a large plateful of vegetable salad or a big bowl of broth-based soup. This is an eating plan you can live with.