Density is a measure of mass per unit of volume. For example, a marshmallow is less dense than a similarly-sized cube of metal. Energy density, with respect to food, denotes a similar relationship. It measures the number of calories per unit of volume. The more calories that are packed into a portion of food, the more energy-dense it is.
Macronutrients
Each macronutrient -- carbohydrates, fats and proteins -- contains units of energy measured as calories. Fat is the most energy-dense of the bunch, weighing in at 9 calories per gram. Carbs and proteins each contain about 4 calories per gram. Fiber, counted as a carbohydrate on food labels, but broken out separately from sugars, contains just 1.5 to 2.5 calories per gram.
Obesity
Direct clinical studies of the causality between diets that are high in energy density and obesity are rare, but energy density as a sub-factor features prominently in studies focused on weight loss, weight maintenance and body mass index, or BMI. In such papers, observational indications are that high energy-dense diets are predictive of higher BMIs, as in a study published in the "American Journal of Clinical Nutrition" in 2005.
Studies of obesity and weight loss appearing in journals such as "Journal of the American Dietetic Association," "American Journal of Clinical Nutrition" and "Obesity Research" between 1991 and 2005 all found a correlation between energy density and obesity, recording weight loss for overweight individuals who switched to low energy-density diets.
Food Items
Vegetables and foods high in fiber are the lowest in energy density, while foods high in fat or consisting primarily of sugars are the most energy-dense, according to the Mayo Clinic. Most fruit contains low to moderate measures of calories per gram, but in all foods, the higher the water content, the lower the energy density. Carrots, for example, are 88 percent water, which adds volume, but no calories, so a full cup of carrots yields only 55 calories. Fats and added sugars common in processed foods, restaurant meals and fast food are the most energy-dense.
Energy Density vs. Nutrient Density
Since the 2005 update to U.S. dietary guidelines published by the Department of Agriculture, or USDA, there has been a keen focus on foods that are nutrient dense. This emphasis highlights foods that provide abundant micronutrients, such as vitamins, minerals and trace elements, and it should not be confused with energy density per se. In fact, there is an inverse relationship between energy-dense foods and nutrient-dense foods. Fruit and vegetables are generally nutrient dense, providing a wide range of vitamins and minerals, but they are low in energy density, as they are generally low in calories.
Socioeconomic Implications
Food choices are often economical, with families and individuals stretching their food budgets to get by. Unfortunately, foods that are fat-rich and high in sugar are typically less expensive than the lean meats, fresh fruit and vegetables associated with a low energy-density diet. As a consequence, cost-constrained diets tend to be higher in energy density and lower in overall diet quality, according to Adam Drewnowski and Nicole Darmon in their analysis of several studies for "The American Journal of Clinical Nutrition" from July 2005.
References
- Mayo Clinic: Energy Density and Weight Loss--Feel Full on Fewer Calories
- University of Florida: Energy Density and Diet Quality
- U.S. Centers for Disease Control and Prevention: Energy Dense Foods and Weight Management
- "The American Journal of Clinical Nutrition"; "The Economics of Obesity: Dietary Energy Density and Energy Cost"; Adam Drewnowski and Nicole Darmon; July 2005
- "European Journal of Clinical Nutrition"; "Energy Density of Food and Beverages ..."; T.C. Crowe et al; June 2004
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