The term nutrient density has several meanings.
Most commonly, nutrient density is defined as a ratio of nutrient content (in grams) to the total energy content (in kilocalories or joules). Nutrient-dense food is opposite to energy-dense food (also called "empty calorie" food). According to the Dietary Guidelines for Americans 2005, nutrient-dense foods are those foods that provide substantial amounts of vitamins and minerals and relatively few calories. Fruits and vegetables are the nutrient-dense foods, while products containing added sugars, processed cereals, and alcohol are not.
Second, nutrient density is defined as a ratio of food energy from carbohydrate, protein or fat to the total food energy. To calculate nutrient density (in percent), divide the food energy (in calories or joules) from one particular nutrient by the total food energy in the given food.
Third, nutrient density is understood as the ratio of the nutrient composition of a given food to the nutrient requirements of the human body. Therefore, a nutrient-dense food is the food that delivers a complete nutritional package.