Common strategies to reduce energy intake include limiting portion sizes, food groups, or certain macronutrients such as carbohydrates or fats. These strategies can help moderate calorie intake, particularly during the short-term; but they do have limitations. These approaches may compromise diet quality or cause feelings of hunger and dissatisfaction, which can limit their acceptability, sustainability, and long-term effectiveness. An alternative strategy for managing calorie intake is to encourage people to eat more foods that are low in calories for a given measure— that is, are low in energy density (kcal/g).

What is energy density?

Energy density is the amount of energy or calories in a particular weight of food (i.e., kcal/g). Foods with a lower energy density provide fewer calories per gram than foods with a higher energy density. For the same amount of calories, a person can consume a larger portion of a lowerenergy-dense food than a food higher in energy density.

Foods with a lower energy density, such as fruits, vegetables, and brothbased soups; tend to have a high water content, lots of fiber, or little fat. Water, which has an energy density of 0 kcal/g, lowers the energy density of foods as it contributes weight but not energy to foods. Fiber also has a relatively low energy density (1.5–2.5 kcal/g). Fat, however, is the most energy dense component of food (9 kcal/g), providing more than twice as many calories as protein or carbohydrates (4 kcal/g). While most high-fat foods have a high energy density, increasing the water content lowers the energy density of all foods, even those high in fat. For example, adding water-rich vegetables to casseroles lowers the energy density of these dishes.

Low-energy-dense diets, energy intake and satiety

Observational studies have shown people who report eating a lowerenergy-dense diet have a lower energy intake yet consume more food by weight than people who eat a higher energy dense diet^(1-3). Experimental studies confirm that consuming foods lower in energy density is an effective strategy for reducing calorie intake and show that calorie intake can be reduced without increasing feelings of hunger. In one of these studies participants were given a standard lunch on different occasions preceded each time with either a first-course salad of differing energy density or by no salad⁽⁴⁾. Participants consumed fewer calories when the meal started with the lower-energy-dense salad and they reported feeling just as full as participants who had no first-course salad or had a salad that was higher in energy density.

Multiple longer-term studies have found that over the course of a few days, people generally consume a fairly consistent amount of food. Therefore, calorie intake is lower when people eat foods low in energy density^(5-10). Encouraging people to eat more foods low in energy density and to substitute these foods for those higher in energy density helps them decrease their caloric intake while eating satisfying portions of food and controlling hunger.

Low-energy-dense diets and body weight

Several observational studies suggest that a relationship exists between consuming an energy dense diet and obesity^{(1, 11-13)}. For example, normal weight adults have been shown to consume diets lower in energy density than obese individuals⁽¹⁾. Additional evidence supporting the use of diets rich in low-energy-dense foods for weight-loss comes from clinical interventions.

Rolls and colleagues⁽¹⁴⁾ examined the effectiveness of incorporating either a low-energy-dense food or a high-energy-dense food into a reducedenergy diet. During this year long trial overweight and obese men and women were provided with one of the following items to incorporate into their daily diet: one serving of soup, two servings of soup, two servings of a dry snack food, or no special food. The researchers found that weight loss was significantly correlated with the overall decrease in the energy density of the diet. Participants consuming two servings per day of lowenergy-dense soup experienced 50% greater weight loss than participants who consumed two servings per day of high-energy-dense dry snacks (7.2 kg vs. 4.8 kg).

In another year-long trial, Ello-Martin and colleagues⁽¹⁵⁾ tested two strategies to reduce the energy density of the diet without providing the subjects with specific calorie limits. One group of obese women was advised to decrease the energy density of their diets by increasing consumption of fruits and vegetables and choosing reduced-fat foods. Another group was counseled only on reducing fat intakes. The group counseled to eat more fruits and vegetables while also reducing fat intake experienced a greater reduction in the energy density of their diets and lost 23% more weight (7.9 kg vs. 6.4 kg). Furthermore, these participants reported consuming more food and experiencing less hunger.

These studies suggest that dietary advice to reduce the energy density of the diet is an effective strategy for weight loss. A benefit of this type of eating plan is that it allows people to eat satisfying amounts of food while restricting their energy intake. Furthermore, it uses positive messages (i.e., eat satisfying portions of low-energy-dense foods) and results in a nutritionally sound eating pattern⁽¹⁶⁾.