When trying to achieve weight loss or when trying to maintain body composition with reduced training (athletes who are in quarantine or athletes who are injured), knowledge about the energy density of foods can be extremely useful.

Energy density of macronutrients

Energy density is the amount of energy or calories in a particular weight of food and is usually presented as kcal/g. Some foods are very energy dense, other foods, usually foods that contain a lot of water and fibre have less energy per gram.

The macronutrients, carbohydrate, fat and protein have different amounts of calories per gram. Alcohol can add energy too.

Energy density of food

Because our foods contain different combinations of these nutrients, they differ vastly in their energy content or energy density. The concept of energy density of foods was popularised by the work of Barbara Rolls and James Stubbs in the 1990s and early 2000s. Their research shows that applying the concept of food energy density can help to guide choices and control hunger while being flexible enough to encompass preferences.

A small quantity of food that is rich in fat will have a very high energy content. Visual cues may not prevent a large intake of energy of such foods. A number of studies have shown that subjects tend to eat a similar weight of food regardless of the macronutrient composition (1). Stubbs and colleagues (1, 2) demonstrated that when subjects received a diet that contained 20%, 40%, or 60% fat and could eat ad libitum, the weight of the food that they consumed was the same. The total amount of energy consumed, however, was significantly different, with the higher-fat diets showing higher intakes. This also resulted in greater weight gain.

Photo from Barbara Rolls. 1575kcal in high energy density foods versus low energy density foods.

Outside of the lab...

This result is also observed in outside the lab. In a representative group of US adults, men and women reported eating a lower energy dense diet ate fewer calories yet consumed more food by weight than people who consumed higher density diets (3, 4, 5). Several large-scale longitudinal and cross-sectional studies involving thousands of participants and a number of review articles have clearly shown that a decrease in energy density results in an increase in energy intake, whereas an increase in energy density results in a decrease in intake (3).

Most of these studies looked at intake in the following meal or 24 hours after the meal, but similar results have been obtained by studies that lasted days or even weeks. These studies provide further evidence that low energy density eating is a successful strategy. In a study by Bell et al (6) normal weight women were provided with all of their meals over 2 days on 3 different occasions. The meals were preparade with different amounts of vegetables so that they differed in energy density. The women ate the same amounts of food by weight, but by doing so reduced their energy intake in the vegetable supplemented meals. Despite the fact that they consumed fewer calories they rated themselves equally full and satisfied.

Normal-weight people consume diets with a lower energy density than obese people and that people who have a high fruit and vegetable intakes have the lowest dietary energy density values and the lowest prevalence of obesity. This is not surprising, because fruits and vegetables generally have high water and fibre contents that provide bulk but less energy than most other food sources.

Manipulating energy density

So, if energy density is such an important factor, how do we manipulate it without changing the taste profile of foods? Only subtle changes to the diet are needed to alter its energy density. Energy density of many popular foods, such as pies, pizzas, sandwiches, and stews, can be decreased without noticeably affecting palatability or portion size by reducing the fat content and adding vegetables and fruits. Modifying food selections this way will also result in healthier eating patterns that are consistent with the dietary guidelines for healthy eating. Education about energy density can be an effective strategy to for weight loss. There are a number of practical ways to decrease the energy density of meals and these will be discussed in the guidelines section.

Eating low energy density foods first

One example is from a study by Barbara Rolls and colleagues (7). They studied a group of 42 women and gave them one of 6 first course salads or no salad. This was then followed by a main meal. The subjects were required to eat the salad but could eat as much or as little pasta in their main meal as they wanted. The salads varied in energy density and in portion size by manipulating the dressing and adding cheese. The results were striking: compared with having no first course, consuming the low energy dense salads reduced meal energy intake by 7-12%, whereas the high energy dense salads increased intake 8-17%. Eating a low energy dense first course thus enhances satiety and reduces meal energy intake and eating a large portion of a low energy dense food at the start of a meal may be a good strategy.

So how can we use knowledge of low and high energy dense foods to our advantage?

Increase variety and availability of low-energy-dense foods:

• Increase intake of high-water foods

• Vegetables, fruits, soups

• Whole grains and legumes

Portion control/limit intake of energy-dense foods:

• High-fat foods

• Foods with low moisture content

• Alcohol

References

1. Stubbs, R. J., Habron, C. G., Murgatroyd, P. R., & Prentice, A. M. (1995). Covert manipulation of dietary fat and energy density: effect on substrate flux and food intake in men eating ad libitum. Am J Clin Nutr, 62, 316-329.

2. Stubbs, R. J., Harbron, C. G., & Prentice, A. M. (1996). Covert manipulation of the dietary fat to carbohydrate ratio of isoenergetically dense diets: effect on food intake in feeding men ad libitum. Int J Obes Relat Metab Disord, 20(7), 651-660.

3. Ledikwe, J. H., Blanck, H. M., Kettel Khan, L., Serdula, M. K., Seymour, J. D., Tohill, B. C., & Rolls, B. J. (2006). Dietary energy density is associated with energy intake and weight status in US adults. Am J Clin Nutr, 83(6), 1362-1368.

4. de Castro, J. M. (2004). Dietary energy density is associated with increased intake in free-living humans. J Nutr, 134(2), 335-341.

5. Drewnowski, A., Almiron-Roig, E., Marmonier, C., & Lluch, A. (2004). Dietary energy density and body weight: is there a relationship? Nutr Rev, 62(11), 403-413.

6. Bell, E. A., Castellanos, V. H., Pelkman, C. L., Thorwart, M. L., & Rolls, B. J. (1998). Energy density of foods affects energy intake in normal-weight women. Am J Clin Nutr, 67(3), 412-420.

7. Rolls, B. J., Roe, L. S., & Meengs, J. S. (2004). Salad and satiety: energy density and portion size of a first-course salad affect energy intake at lunch. J Am Diet Assoc, 104(10), 1570-1576.