7. The Volumetrics diet
The Volumetrics diet was created by Penn State University nutrition professor Barbara Rolls and is meant to be a long-term lifestyle change rather than a strict diet.

How it works
The eating plan is designed to promote weight loss by having you fill up on nutrient-dense foods that are low in calories and high in water.

Meanwhile, it limits calorie-dense foods like cookies, candies, nuts, seeds, and oils.

The Volumetrics diet divides food into four categories based on food’s calorie density, which can be calculated with a formula created by Rolls. These categories are:

Category one: includes foods of very low calorie density, like non-starchy fruits and vegetables, nonfat milk, and broth-based soup
Category two: includes low calorie-dense foods, like starchy fruits and vegetables, grains, breakfast cereal, low fat meat, legumes, and low fat mixed dishes like chili
Category three: includes medium calorie-dense foods, like meat, cheese, pizza, bread, and ice cream
Category four: includes high calorie-dense foods, like crackers, chips, chocolate candies, nuts, butter, and oil
Meals on the Volumetric diet consist mostly of foods from categories one and two, with limited amounts of food from categories three and four.

No foods are completely off-limits on the Volumetrics diet, and exercise is encouraged for at least 30–60 minutes each day.

Health benefits
The Volumetrics diet encourages nutritious foods that are low in calories but high in fiber, vitamins, and minerals, which may help increase your intake of key nutrients and protect against nutritional deficiencies.

Research also links diets with a low calorie density to improved diet quality (37Trusted Source).

Additionally, it limits the amount of processed foods you’ll eat, which can decrease your risk of developing certain cancers and heart disease (38Trusted Source, 39Trusted Source).

The Volumetrics diet may also help you lose weight.

A review of 13 studies in more than 3,000 people found that diets rich in low calorie density foods led to increased weight loss. Similarly, an 8-year study in more than 50,000 women found that high calorie-dense foods led to increased weight gain (40Trusted Source, 41Trusted Source).

Downsides
While the Volumetrics diet may be effective for health benefits and weight loss, it requires a good understanding of Volumetrics, which involves learning about the calorie levels of foods in relation to portion sizes and nutrient levels.

This may be easier for some compared to others.