According to nutritionist and co-author Barbara Rolls, Ph.D., it was believed that people instinctively consumed the same number of calories over a span of a few days. Now, cites Rolls, new research shows that "people eat the same amount, or weight of food, over a couple of days." So, if you eat the same amount of food but make more nutritious choices, "you'll feel full on fewer calories," says Rolls.
How does dense food fill you up? As the stomach fills, it contracts rhythmically, breaking food into tiny particles that can pass into the intestines. These contractions, says Rolls, are "part of satiety, and they are similar, whether breaking down a pound of food that has 500 calories or a pound that has 1,500 calories." A large volume of food also facilitates the release in the small intestine of cholecystokinin—one of several "satiety hormones" that signal a full stomach. The larger the volume of food, the more hormone is released and the longer you stay sated.
Rolls recommends relying on foods with a low energy density, or E.D., which is calculated by dividing a food's calories by its weight in grams. For example, a serving of 115-calorie frozen yogurt that weighs 72 g has a relatively low E.D. of 1.6. Other low-E.D. foods include high-in-water vegetables, fruits, pasta, and grains; on the high end of the spectrum are potato chips, vegetable oils, crackers, and mayonnaise. This discipline is not without its surprises: You might be shocked to know that three rice cakes have a higher E.D. (3.9) than a McDonald's Egg McMuffin (2.1).
In addition to recipes and meal plans, Rolls offers slimming strategies that include decreasing your intake of sugary drinks (adds calories with little satiety), and increasing your daily fiber intake to 20 to 30 g and water to nine to 12 cups. She also recommends eating more broth-based soups, since studies show it to help people consume fewer calories. "You believe soup to be satisfying compared to, say, a melon, which seems like diet food," says Rolls.
The best part of the Volumetrics plan is that dieters needn't forgo their favorite treats. "I've lost seven pounds," says Rolls, "and I still have a little chocolate, and some wine with dinner."