Essential nutrient

An essential nutrient is a nutrient required for normal human body function that either cannot be synthesized by the body at all, or cannot be synthesized in amounts adequate for good health (e.g. niacin, choline), and thus must be obtained from a dietary source. Essential nutrients are also defined by the collective physiological evidence for their importance in the diet, as represented in e.g. US government approved tables for Dietary Reference Intake.[1]

Some categories of essential nutrients include vitamins, dietary minerals, essential fatty acids, and essential amino acids. Different species have very different essential nutrients. For example, most mammals synthesize their own ascorbic acid, and it is therefore not considered an essential nutrient for such species. It is, however, an essential nutrient for human beings, who require external sources of ascorbic acid (known as Vitamin C in the context of nutrition).

Many essential nutrients are toxic in large doses (see hypervitaminosis or the nutrient pages themselves below). Some can be taken in amounts larger than required in a typical diet, with no apparent ill effects.

For humans

Fatty acids

Essential fatty acids cannot be synthesized by humans, as humans lack the desaturase enzymes required for their production.

α-Linolenic acid is not used by the body in its original form. It is converted by the body into the required long-chain polyunsaturated fatty acids eicosapentaenoic acid (EPA, 20:5) and docosahexaenoic acid (DHA, 22:6). EPA and DHA can also be consumed from a direct source by consuming fish, fish oil or algal oil (vegetarian source).

Linoleic acid is not used by the body in its original form either. It is converted by the body into the required long-chain polyunsaturated fatty acids gamma-linolenic acid (GLA, 18:3), dihomo-gamma-linolenic acid (DGLA, 20:3) and arachidonic acid (AA, 20:4).

Amino acids

Carbohydrates

Carbohydrates are sugar molecules and chains of sugar molecules. Although no individual carbohydrate by itself is an essential nutrient in humans,[3] mixed complex carbohydrates are essential for growth and development, especially during the infant years.[4] As a general dietary recommendation, an expert scientific panel of the European Food Safety Authority reported that carbohydrates should supply 45–60% of daily energy as the reference intake.[5]

Glucose can be supplied 1) by carbohydrate digestion, 2) by synthesis from amino acids and glycerol obtained from fat metabolism or 3) by de novo synthesis (called gluconeogenesis) which, without a concurrent carbohydrate supply, depletes nitrogen stores and is insufficient to maintain normal brain metabolism alone.[6] However, the body can adapt to this state by producing ketones (a state called ketosis) to fuel the brain, which can only use glucose and ketones for fuel, unless carbohydrate stores are repleted.[3]

For humans, glucose is the key source of energy via aerobic respiration, providing about 3.75 kilocalories (16 kilojoules) of food energy per gram.[7]

Vitamins

Dietary minerals

Other

For plants

Main article: Plant nutrition

See also

References

  1. ↑ "National Academy of Sciences. Institute of Medicine. Food and Nutrition Board. Dietary Guidance: DRI Tables". US Department of Agriculture, National Agricultural Library and National Academy of Sciences, Institute of Medicine, Food and Nutrition Board. December 2001.
  2. ↑ J D Kopple and M E Swendseid (May 1975). "Evidence that histidine is an essential amino acid in normal and chronically uremic man.". J Clin Invest. 55 (5): 881–891. doi:10.1172/JCI108016. PMC 301830. PMID 1123426.
  3. ↑ 3.0 3.1 Westman, EC (2002). "Is dietary carbohydrate essential for human nutrition?". American Journal of Clinical Nutrition 75 (5): 951–3; author reply 953–4. PMID 11976176.
  4. ↑ Stephen A et al. (2012). "The role and requirements of digestible dietary carbohydrates in infants and toddlers". Eur J Clin Nutr 66 (7): 765–79. doi:10.1038/ejcn.2012.27. PMC 3390559. PMID 22473042.
  5. ↑ "Scientific Opinion on Dietary Reference Values for carbohydrates and dietary fibre" (PDF). European Food Safety Authority, printed from EFSA Journal 2010; 8(3):1462. 2010. Retrieved 10 December 2014.
  6. ↑ Kalhan SC, Kiliç I (1999). "Carbohydrate as nutrient in the infant and child: range of acceptable intake". Eur J Clin Nutr 53 (Suppl 1): S94–100. PMID 10365985.
  7. ↑ "Chapter 3: Calculation of the Energy Content of Foods – Energy Conversion Factors", Food energy — methods of analysis and conversion factors, FAO Food and Nutrition Paper 77, Rome: Food and Agriculture Organization of the United Nations, 2003, ISBN 92-5-105014-7
  8. ↑ "National Academy of Sciences. Institute of Medicine. Food and Nutrition Board. Dietary Reference Intakes: Elements". US Department of Agriculture, National Agricultural Library and National Academy of Sciences, Institute of Medicine, Food and Nutrition Board. October 2009.
  9. ↑ R. Bruce Martin "Metal Ion Toxicity" in Encyclopedia of Inorganic Chemistry, Robert H. Crabtree (Ed), John Wiley & Sons, 2006. doi:10.1002/0470862106.ia136