WHAT IS ENERGY DENSITY AND HOW IS IT MEASURED?
Energy density is defined as the amount of energy (kilocalorie) in a given weight (gram) of food and is expressed as kilocalorie per gram. Foods can be categorized as having very low, low, medium, or high energy density, as shown in Table 1 (9).
HOW DOES A LOW ENERGY DENSE DIET WORK?
Consuming a diet composed of lower energy-dense foods may promote weight loss in two key ways. First, low energy dense foods are high in water and fiber, thus, these foods have a greater volume that occupies more space in the stomach, making you feel full. Second, low energy dense foods are as satiating as high energy dense foods while being lower in kilocalories per gram of food consumed. Thus, a meal composed of low energy dense foods will be lower in calories while making you feel just as satisfied with your meal (10).
Overall, the impact of a low energy dense diet means that you can consume a greater volume of food and feel more satiated while still reducing total energy intake. Table 2 compares commonly consumed foods and how they differ in weight, total kilocalories, and energy density (kilocalories per gram). If very low or low energy dense foods are chosen more frequently, larger portions of food can be consumed, resulting in greater satiety. When consuming foods that are medium and high in energy density, choosing smaller portions of nutrient-dense foods from these categories (i.e., whole grain breads, dried fruits, nuts, nut butters) is important to maintain a lower energy intake. In summary, a key component of a low energy dense eating plan is to increase intake of foods high in water and fiber to promote satiation while reducing high-fat foods (i.e., potato chips, cheese, cookies) and low-water/fiber foods (i.e., baked potato chips, tortilla chips, pretzels). Although some of these foods may be lower in fat, without a high water and fiber content, they are not as satiating (2,10).
WHAT DOES RESEARCH SHOW?
Researchers from Pennsylvania State University have done extensive work in examining the short- and long-term effectiveness of a low energy dense eating plan on energy intake and weight loss (1,2,12–15). For example, early work demonstrated the impact of a low energy dense diet on energy intake (1). First, researchers provided normal-weight women with all their meals for 2 days using three separate testing conditions where the food provided differed in energy density. Each session measured the total amount of food consumed by weight (grams) and total energy intake (kilocalories) for three different conditions of energy density: 1) low, 2) medium, and 3) high. To alter energy density, the proportion of vegetables in the main entrée was either increased or decreased; the low energy dense condition had the greatest water content. Across all test conditions, the women ate a similar amount and weight of food, but 30% more energy was consumed in the high energy dense condition (1,800 kcal · day−1) than in the low energy dense condition (1,376 kcal · day−1). Furthermore, the women did not report any differences in hunger and fullness ratings or enjoyment of the meals across test conditions.
In a follow-up study, researchers examined the effects of changing portion size and energy density on total energy intake during a 2-day period in young women (15). Four different dietary conditions were tested to determine the condition that resulted in the greatest reduction of energy intake, thus, resulting in the greatest weight loss if followed long-term. The four different conditions are given below:
Energy density was again altered by changing the portions of vegetables in entrées and by substituting low-fat foods/ingredients for full-fat foods (e.g., low-fat milk instead of full-fat milk). The researchers found that the effects of energy density and portion size were independent of one another. When only the effect of reducing portion size was examined, it reduced energy intake by −231 kcal · day−1 (Figure 1) (15). However, when the effect of only reducing energy density was examined, it reduced energy intake by −575 kcal · day−1 (Figure 1). Furthermore, the foods provided under condition 2 (normal portions; reduced energy density) and condition 3 (reduced portions; normal energy density) provided the same energy (total kilocalories), but they differed in portion sizes and energy density. This allowed the researchers to directly compare the effects of reducing portion size and energy density on energy intake. In condition 2, where portions were maintained but energy density was reduced, total energy intake (1,937 kcal · day−1) was lower (−288 kcal · day−1) than total energy intake (2,225 kcal · day−1) in condition 3, where portion sizes were reduced, but energy density did not change (Figure 2). Overall, changing the energy density of the diet reduced energy intake more than reducing portion sizes. In addition, although reducing the energy density was more effective at lowering energy intake than reducing portion size, it did not impact ratings of hunger, fullness, or enjoyment of the food. For individuals trying to lose weight, this has important implications. It may be easier for people to consume a similar amount of food and focus on changing the energy density of their diet rather than eating smaller portion sizes. For example, a person attempting to lose weight could eat the same amount of soup or casserole, but make the food with more vegetables, so that each serving is lower in kilocalories.
The previous research was short-term (2 days), but research also has demonstrated the effectiveness of reducing energy density for long-term weight loss. For example, researchers compared two different low-fat diets (∼28% of energy from fat) that varied in energy density (3). One group of overweight/obese women only reduced its fat intake (RF), whereas the other group reduced its fat intake and increased its intake of fruits and vegetables (RF + FV). The RF + FV group reduced dietary energy density to a greater extent compared with that of the RF group (RF = 1.45 kcal · g−1 vs. RF + FV = 1.23 kcal · g−1). Both groups lost weight (RF = −6.7 kg; RF + FV = −8.9 kg), but the RF + FV group lost 33% more weight (−2.3 kg) at 6 months and maintained a lower body weight for the duration of the 1-year study (difference of 1.5 kg at 12 months; Figure 3) compared with the RF group.
The Dietary Approaches to Stop Hypertension (DASH [www.dashdiet.org]) is another low energy dense eating plan that can produce weight loss. Researchers examined the effect of the DASH diet with overweight hypertensive adults for 6 months (8). Individuals following the DASH eating plan had a dietary energy density of 1.22 kcal · g−1, whereas those following the energy restricted only diet had a dietary energy density of 1.54 kcal · g−1. When participants were divided into three groups based on reductions in energy density from baseline, results showed that individuals who decreased their energy density the most (−0.52 kcal · g−1 or more; average −0.9 kcal · g−1; −43% reduction in energy density) experienced the greatest amount of weight loss (−5.9 kg vs. −4.0 kg vs. −2.4 kg across tertiles of energy density). Larger reductions in energy density were related to increases in whole fruits and vegetables and fiber and decreases in fat and saturated fat intake.
The role of a low energy dense diet for weight maintenance also has been examined. In a 2-year follow-up study following initial weight loss, in which low energy dense foods were encouraged, dietary energy density was compared between weight maintainers (regain of <5% of postintervention body weight) and weight gainers. Researchers found that those who maintained or continued to lose weight at follow-up consumed a diet lower in energy density (1.67 kcal · g−1) than those who regained weight (1.98 kcal · g−1) (5).
What do these findings mean for individuals trying to lose or maintain weight? The key take-home points from this research are bulleted below:
* Reducing dietary energy density can reduce energy intake while maintaining satiety.
* Low energy dense diets are effective in the prevention of weight regain after weight has been lost.
* Reducing dietary energy density may be more effective at decreasing energy intake than reducing portion size alone.
* Individuals who are able to more substantially reduce energy density may experience greater weight loss.
* A low energy dense diet can be a healthy eating plan that can be maintained long-term and positively improve overall health.
HOW DO YOU IMPLEMENT A LOW ENERGY DENSE EATING PATTERN?
Altering the energy density of your diet is simpler than you think. See Table 3 for sample menus for a high versus low energy dense eating plan. You can see that a greater amount and weight of food can be consumed for a similar energy intake. Further reductions in portion sizes, limiting higher energy density foods (avocado, dressings), and substituting high-fat foods for low-fat options will lower the overall energy intake without substantially reducing the amount of food consumed. Table 4 also identifies steps and strategies your clients can follow to reduce dietary energy density.
Reducing dietary energy density can be an effective way to reduce total energy intake and promote weight loss and the prevention of weight regain after weight has been lost. Replacing higher calorie foods (i.e., potato chips) with low-calorie, low energy dense foods (i.e., apple, grapes, carrots) can lessen feelings of hunger often associated with reducing portion sizes and reducing total energy intake. Research indicates that low energy dense foods decrease energy intake and promote weight loss in both short- and long-term studies. Any dietary behaviors that promote weight loss must be sustainable for continued weight maintenance. Finally, consuming a reduced energy dense diet and increased physical activity can be the key to successfully achieving a healthy body weight. These lifestyle changes can help sustain a healthy weight for a lifetime.
CONDENSED VERSION AND BOTTOM LINE
Many individuals struggle to lose weight and maintain the weight loss long-term. Following a low energy dense diet high in whole fruits and vegetables, whole grains, and low-fat dairy and meats can be an effective method to reduce energy intake while maintaining satisfying portions. This dietary approach, when combined with increased physical activity, may result in the ability to reduce energy intake, facilitating better success at weight loss and the prevention of weight regain.
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Keywords:© 2012 American College of Sports Medicine
Dietary Strategies; Energy Intake; Weight Management; Whole Grains; Fruits and Vegetables; Fiber