Nutrient: Substance that an organism uses to live

A nutrient is essential to an organism if it cannot be produced by the organism and must be obtained from a food source.

This article deals with nutrition in animals, especially humans. Nutrition in plants, fungi, bacteria and archaea is not discussed here.

• Carbohydrates are compounds made of sugars. Carbohydrates are named by the number of sugar units they have.

Monosaccharides (such as glucose and fructose) have one.
Disaccharides (such as sucrose and lactose) have two.
Oligosaccharides, and polysaccharides (such as starch, glycogen, and cellulose) have more.

• Proteins are organic compounds that are amino acids joined by peptide bonds. The body cannot make some of these; so they must come from food. In the body, proteins are broken down through digestion back into free amino acids.
• Fats are a glycerin molecule with three fatty acids attached. Fats are needed to keep cell membranes functioning properly, to insulate body organs against shock, to keep body temperature stable, and to maintain healthy skin and hair. The body does not manufacture certain fatty acids and the diet must supply these.

These three types of nutrients are often called macronutrients.

• Minerals are generally trace elements, salts, or ions such as copper and iron. These minerals are essential to human metabolism.
• Vitamins are organic compounds essential to the body. They usually act as coenzymes or cofactors for various proteins in the body.
• Water is an essential nutrient and is the solvent in which all the chemical reactions of life take place.

The following table gives an idea of what elements are essential for humans:

Periodic table highlighting dietary elements

• Eutrophication