Volumetrics

Volumetrics was developed by Dr. Barbara Rolls, the Helen A. Guthrie Chair in Nutrition at Penn State University, based on decades of research into satiety and eating behavior. Its central idea is energy density — calories per gram of food. People tend to eat a fairly consistent weight of food each day regardless of its calorie content, largely because water and fiber add bulk and fullness without adding calories. Choose more foods with a lot of water and fiber per calorie, and you can eat a similar volume of food — and feel similarly full — while taking in fewer calories overall, without consciously restricting.

Volumetrics groups foods into four rough density tiers rather than banning any of them:

• Very low density — broth-based soups, non-starchy vegetables, most fruits
• Low density — starchy vegetables, whole grains, legumes, low-fat dairy, lean protein
• Medium density — meat, cheese, pizza, ice cream, bread, salad dressing
• High density — chips, crackers, chocolate, cookies, nuts, butter, oil

The approach isn't to eliminate the higher-density tiers — nuts and oil, for instance, are nutritionally valuable in moderation — but to build most meals around the lower-density tiers so total calorie intake drops while the amount of food on the plate, and the feeling of fullness, stays about the same.

Volumetrics is one of the more directly research-backed approaches on this page — it comes out of a specific, decades-long university research program rather than being reverse-engineered from a popular book.

Primary trial: Ello-Martin JA, Roe LS, Ledikwe JH, Beach AM, Rolls BJ. "Dietary energy density in the treatment of obesity: a year-long trial comparing 2 weight-loss diets," American Journal of Clinical Nutrition, 2007. A year-long RCT in 97 obese women (71 completed): one group was coached to reduce fat intake (RF), the other to reduce fat and deliberately increase water-rich fruits and vegetables to further lower energy density (RF+FV). The RF+FV group lost significantly more weight (7.9±0.9 kg vs. 6.4±0.9 kg) and reported significantly lower hunger — direct evidence that lowering energy density helps people stick with a deficit via satiety, not just willpower.

Read the trial →

The book: Rolls, B. (with Hermann, M.) (2012). The Ultimate Volumetrics Diet: Smart, Simple, Science-Based Strategies for Losing Weight and Keeping It Off. HarperCollins. This is the consumer-facing distillation of Dr. Rolls' research program, not a separate primary source — the trial above is the underlying evidence.

Rankings: U.S. News & World Report has repeatedly placed Volumetrics among its top diets for weight loss — Penn State's own reporting on the annual rankings has described it placing in the top few weight-loss diets for over a decade running, most recently noted specifically for "fullness per calorie." As with any expert-panel ranking, this reflects a panel's structured judgment across criteria like ease of use and nutritional adequacy, not a single trial outcome.

Very low density (build meals around these): broth-based vegetable soup, leafy greens, cucumber, tomatoes, berries, melon, non-fat plain yogurt.

Low density (good everyday staples): potatoes, brown rice, oats, beans and lentils, skinless chicken breast, fish, low-fat cheese.

Medium density (fine in reasonable portions): lean beef, regular cheese, whole eggs, bread, pasta, salad dressing.

High density (enjoy in smaller amounts, not eliminated): nuts, seeds, dried fruit, oils and butter, chips, chocolate, cookies.

Breakfast: oatmeal made with water or non-fat milk, topped with berries.

Lunch: a large vegetable-and-bean salad with a light vinaigrette, plus a piece of fruit.

Dinner: a broth-based vegetable soup as a starter, followed by grilled chicken or fish with a large portion of roasted vegetables and a smaller portion of rice.

Snack: a small handful of nuts or a square of dark chocolate — the higher-density tier, in a controlled portion rather than eliminated.

Tends to suit people who find restriction-based dieting hard to sustain because they end up hungry — the appeal here is eating a similar volume of food, and feeling similarly full, for fewer calories. It requires some attention to a food's water and fiber content rather than following a fixed food list, which suits people who like understanding the "why" behind a recommendation more than people who want simple binary rules. It may not suit anyone looking for a fully hands-off plan, since some awareness of energy density (or, practically, calories per serving) is part of how it works day to day.

Penn State College of Health and Human Development — Dr. Barbara Rolls

U.S. News & World Report — Volumetrics Diet Overview