Caloric density

Energy density is the amount of energy per unit mass or volume of food. The energy density of a food can be determined from the label by dividing the energy per serving (usually in kilojoules or Calories) by the serving size (usually in grams, milliliters, or fluid ounces). An energy unit commonly used in nutritional contexts within non-metric countries (e.g., the United States) is the "dietary calorie," "food calorie," or "Calorie" with a capital "C" and is commonly abbreviated as "Cal." A nutritional Calorie is equivalent to a thousand chemical or thermodynamic calories (abbreviated "cal" with a lowercase "c") or one kilocalorie (kcal). Because food energy is commonly measured in Calories, the energy density of food is often called "caloric density." In the metric system, the energy unit commonly used on food labels is the kilojoule (kJ) or megajoule (MJ). Energy density is thus commonly expressed in metric units of cal/g, kcal/g, J/g, kJ/g, MJ/kg, cal/mL, kcal/mL, J/mL, or kJ/mL.

Determination of energy density

Energy density measures the energy released when the food is metabolized by a healthy organism when it ingests the food (see food energy for calculation). In aerobic environments, this typically requires oxygen as an input and generates waste products such as carbon dioxide and water.

Besides alcohol, the only sources of food energy are carbohydrates, fats, and proteins, which make up ninety percent of the dry weight of food. Therefore, water content is the most important factor in computing energy density. In general, proteins have lower energy densities (~16 kJ/g) than carbohydrates (~17 kJ/g), whereas fats provide much higher energy densities (~38 kJ/g), approximately 2.25 times as much energy. Fats contain more carbon-carbon and carbon-hydrogen bonds than carbohydrates or proteins, yielding higher energy density.

Energy density of different foods

Foods that derive most of their energy from fat have a much higher energy density than those that derive most of their energy from carbohydrates or proteins, even if the water content is the same. Nutrients with a lower absorption rate, such as fiber or sugar alcohols, lower the energy density of foods as well. A moderate energy density would be 1.6 to 3 Calories per gram (7–13 kJ/g); examples include salmon, lean meat, and bread. Foods with high energy density have more than three Calories per gram (>13 kJ/g) and include crackers, cheese, chocolate, nuts, and fried foods like potato chips or tortilla chips.

See also

• Glycemic index
• Nutrient density
• Macronutrients
• Dieting
• Metabolism