Nutrients are the components in foods that an organism utilizes to survive and grow. Macronutrients provide the bulk energy for an organism's metabolic system to function, while micronutrients provide the necessary cofactors for metabolism to be carried out. Both types of nutrients can be acquired from the environment. They are used to build and repair tissues, regulate body processes, and are converted to and used for energy. Methods for nutrient intake are different for plants and animals. Plants take in nutrients directly from the soil through their roots and from the atmosphere through their leaves. Animals and protists have specialized digestive systems that work to break down macronutrients for energy and utilize micronutrients to carry out both metabolism and anabolism or constructive synthesis in the body.
Types of nutrient
Macronutrients are defined in several different ways.
- The chemical elements humans consume in the largest quantities are carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulphur, or CHNOPS.
- The classes of chemical compounds humans consume in the largest quantities and which provide bulk energy are carbohydrates, proteins, and fats. Water and atmospheric oxygen also must be consumed in large quantities, but are not always considered "food" or "nutrients".
- Calcium, salt (sodium and chloride), magnesium, and potassium (along with phosphorus and sulfur) are sometimes added to the list of macronutrients because they are required in large quantities compared to other vitamins and minerals. They are sometimes referred to as the macrominerals.
Substances that provide energy
- Carbohydrates are compounds made up of types of sugars. Carbohydrates are classified by their number of sugar units: monosaccharides (such as glucose and fructose), disaccharides (such as sucrose and lactose), oligosaccharides, and polysaccharides (such as starch, glycogen, and cellulose).
- amino acids joined by peptide bonds. The body cannot manufacture some of the amino acids (termed essential amino acids); the diet must supply them. Proteins, in nutrition, are broken down through digestion by proteases back into free amino acids.
- essential fatty acids) and the diet must supply them.
Although alcohol provides energy, and can thus be compared to macronutrients, it is not a substance that is essential for normal function. The acetic acid in vinegar also provides a similar amount of energy per gram, but again, it is not a nutrient because it is not essential for normal function.
Substances that support metabolism
- Dietary minerals are generally trace elements, salts, or ions such as copper and iron. Some of these minerals are essential to human metabolism.
- 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.
Plants absorb nutrients from the soil or the atmosphere, or from water (mainly aquatic plants). An exception are the carnivorous plants, which externally digest nutrients from animals before ingesting them.
The chemical elements consumed in the greatest quantities by plants are carbohydrates, lipids, proteins) compounds, although elemental diatomic molecules of nitrogen and (especially) oxygen are often used.
Some of these are considered macronutrients in certain organisms. The mnemonic C. HOPKN'S CaFe Mg (to be used as C. Hopkins coffee mug) is used by some students to remember the list as: carbon, hydrogen, oxygen, phosphorus, potassium, nitrogen, sulfur, calcium, iron, and magnesium. Silicon, chloride, sodium, copper, zinc, and molybdenum are sometimes also included, but are in other cases considered micronutrients.
Essential and non-essential nutrients
Nutrients are frequently categorized as essential and nonessential.  Nonessential nutrients are those nutrients that can be made by the body; they may often also be absorbed from consumed food. The majority of animals ultimately derive their essential nutrients from plants, though some animals may consume mineral-based soils to supplement their diet.
For humans, these include essential fatty acids, essential amino acids, vitamins, and certain dietary minerals. Oxygen and water are also essential for human survival, but are generally not considered "food" when consumed in isolation.
Non-essential substances within foods can still have a significant impact on health, whether beneficial or toxic. For example, most dietary fiber is not absorbed by the human digestive tract, but is important in digestion and absorption of otherwise harmful substances. Interest has recently increased in phytochemicals, which include many non-essential substances which may have health benefits.
Deficiencies and toxicity
An inadequate amount of a nutrient is a deficiency. Deficiencies can be due to a number of causes including inadequacy in nutrient intake called dietary deficiency, or conditions that interfere with the utilization of a nutrient within an organism. Some of the conditions that can interfere with nutrient utilization include problems with nutrient absorption, substances that cause a greater than normal need for a nutrient, conditions that cause nutrient destruction, and conditions that cause greater nutrient excretion.
Nutrient toxicity occurs when an excess of a nutrient does harm to an organism.
In plants five types of deficiency or toxicity symptoms are common:
- Chlorosis - which is the yellowing of plant tissue caused by a shortage of chlorophyll synthesis.
- Necrosis - which is the death of tissue.
- Accumulation of anthocyanin - which produces a purple or reddish colorization of foliage and/or stems.
- Lack of new growth.
- Stunting or reduced growth - where new growth is stunted or reduced.classify*
Oversupply of plant nutrients in the environment can cause excessive plant and algae growth. Eutrophication, as this process is called, may cause imbalances in population numbers and other nutrients that can be harmful to certain species. For example, an algal bloom can deplete the oxygen available for fish to breathe. Causes include water pollution from sewage or runoff from farms (carrying excess agricultural fertilizer). Nitrogen and phosphorus are most commonly the limiting factor in growth, and thus the most likely to trigger eutrophication when introduced artificially.
- Essential nutrient
- List of macronutrients
- List of micronutrients
- List of phytochemicals in food
- Agricultural Research Service
- Ecological sanitation
- Food composition
- Nutrient density
- Nutrients (journal)
- Whitney, Elanor and Sharon Rolfes. 2005. Understanding Nutrition, 10th edition, p 6. Thomson-Wadsworth.
- FRANCES SIZER; ELLIE WHITNEY (12 November 2007). NUTRITION: CONCEPTS AND CONTROVERSIES. Cengage Learning. pp. 26–.
- Audrey H. Ensminger (1994). Foods & nutrition encyclopedia. CRC Press. pp. 527–.
- Mark Kern (12 May 2005). CRC desk reference on sports nutrition. CRC Press. pp. 117–.
- Coyle EF. 1995. Fat metabolism during exercise. Sports science exchange 8(6):59-65
- David Sadava; H. Craig Heller; David M. Hillis; May Berenbaum (2009). Life: The Science of Biology. Macmillan. pp. 767–.
- J. Benton Jones (1998). Plant nutrition manual. CRC Press. pp. 34–.
- New Link in Chain of Life, Wall Street Journal, 2010-12-03, accessed 2010-12-05. "Until now, however, they were all thought to share the same biochemistry, based on the Big Six, to build proteins, fats and DNA."
- CHNOPS: The Six Most Abundant Elements of Life, Pearson BioCoach, 2010, accessed 2010-12-09. "Most biological molecules are made from covalent combinations of six important elements, whose chemical symbols are CHNOPS. ... Although more than 25 types of elements can be found in biomolecules, six elements are most common. These are called the CHNOPS elements; the letters stand for the chemical abbreviations of carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur."
- Perry, David A (1994). Forest ecosystems. Baltimore: Johns Hopkins University Press.
- John Griffith Vaughan; Catherine Geissler; Barbara Nicholson; Elisabeth Dowle, Elizabeth Rice (2009). The new Oxford book of food plants. Oxford University Press US. pp. 212–.
- "Essential Plant Nutrients". Cartage.org.lb. Retrieved 2012-10-17.