The secret lies in the concentration of calories in portions of food, a concept she calls "energy density." There are foods with low-energy density (which are good for you) and foods with high-energy density (which are not in fact).

Low-energy density foods allow you to eat heaping portions without consuming a great deal of calories. High-energy density foods, on the other hand, leave you feeling deprived since a small amount has an excessive amount of calories. You get a greater amount of calories for less food.

Dr. Rolls' innovative system makes the body feel full by consuming foods that contain fewer calories but have more bulk. For example, 1 cup of raisins and 1 2/3 cups of grapes both have 100 calories. Yet it is the grapes that will leave the stomach feeling fuller for a longer period of time. When following Volumetrics, it is important to select foods that have the most volume for the number of calories.

Volumetrics stresses the importance of high-fiber foods -- for both their health properties and high water content which makes the body feel full. Foods that cause the body to feel satiated are tomatoes, fresh fruits, broccoli, greens, casseroles, soups and salads. Other foods advocated on the Volumetrics plan include whole grain pasta, rice, breads and cereals, low-fat poultry, seafood, meats and dairy.

Also, say goodbye to fried foods, sweets, fats and processed foods that include crackers and pretzels. These foods have decent amounts of calories per small serving but leave you feeling hungry.