The term nutrient density has several meanings.

Most commonly, nutrient density is defined as a ratio of nutrient

Nutrient

A nutrient is a chemical that an organism needs to live and grow or a substance used in an organism's metabolism which must be taken in from its environment. They are used to build and repair tissues, regulate body processes and are converted to and used as energy...

 content (in grams) to the total energy content (in kilocalories or joule

Joule

The joule ; symbol J) is a derived unit of energy or work in the International System of Units. It is equal to the energy expended in applying a force of one newton through a distance of one metre , or in passing an electric current of one ampere through a resistance of one ohm for one second...

s). Nutrient-dense food is opposite to energy-dense food (also called "empty calorie

Empty calorie

Empty calories, in casual dietary terminology, are a measurement of the energy present in high-energy foods with poor nutritional profiles, with most of the energy typically coming from processed carbohydrates, fats, or ethanol...

" 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 sugar

Sugar

Sugar is a class of edible crystalline carbohydrates, mainly sucrose, lactose, and fructose, characterized by a sweet flavor.Sucrose in its refined form primarily comes from sugar cane and sugar beet...

s, processed cereals, and alcohol

Alcohol

In chemistry, an alcohol is an organic compound in which the hydroxy functional group is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms....

 are not.

Second, nutrient density is defined as a ratio of food energy from carbohydrate

Carbohydrate

A carbohydrate is an organic compound with the empirical formula ; that is, consists only of carbon, hydrogen, and oxygen, with a hydrogen:oxygen atom ratio of 2:1 . However, there are exceptions to this. One common example would be deoxyribose, a component of DNA, which has the empirical...

, protein

Protein

Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

 or fat

Fat

Fats consist of a wide group of compounds that are generally soluble in organic solvents and generally insoluble in water. Chemically, fats are triglycerides, triesters of glycerol and any of several fatty acids. Fats may be either solid or liquid at room temperature, depending on their structure...

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.