An eating approach that promises weight loss without cutting portion sizes is drawing renewed attention. U.S. health magazine Men's Health recently spotlighted the Volumetrics diet, which fills the plate with foods high in water and fiber to sustain a feeling of fullness rather than slashing calories.
Volumetrics was developed around 2000 by Barbara Rolls, a professor of nutritional sciences at Pennsylvania State University. Rolls, who heads the university's Laboratory for the Study of Human Ingestive Behavior, has studied the relationship between satiety and calorie density. The diet has ranked near the top of the annual "Best Diets" list published by U.S. News & World Report every year since 2011, and took first place in the weight-loss category in 2022.
The central concept is calorie density, or the number of calories in one gram of food. Vegetables and fruits high in water and fiber carry fewer calories relative to their weight, so the same volume delivers less energy. Foods high in fat, by contrast, pack many calories into a small amount. The approach differs from the more familiar idea of "empty calories." While the empty-calorie framework focuses on cutting foods such as soda and snacks that deliver calories without nutrition, Volumetrics weighs volume and density ahead of whether a food is inherently good or bad. Nuts, for instance, are classified as items to limit despite their nutritional value, because their density is high.
The diet sorts foods into four categories by calorie density. Category 1 covers the least dense foods — berries, melon, broccoli, carrots, nonfat yogurt and broth-based soups — and is meant to make up a substantial share of each meal. Category 2 includes lean meat, lentils, chickpeas, potatoes and brown rice, to be eaten in moderate amounts. Category 3 covers cheese, fatty meats, pasta and bread, which require portion control. Category 4 consists of nuts, seeds, oils, fast food and candy, to be eaten only in small quantities.
Rolls' research team has published findings showing that participants who ate broth-based soup before a meal consumed fewer calories overall while reporting the same level of fullness. The explanation is that people tend to eat a fairly consistent weight or volume of food at a meal, so lowering density reduces total calorie intake even when the amount stays the same.
The approach has its limits. Not every calorie-dense food is unhealthy. Nuts, seeds and olive oil rank high in density but supply essential fatty acids and other nutrients. Experts note that calorie density alone cannot determine a food's quality, and that the framework risks overly restricting intake of healthy fats.
