A nutrient is a substance used by an organism to survive, grow, and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi, and protists. Nutrients can be incorporated into cells for metabolic purposes or excreted by cells to create non-cellular structures, such as hair, scales, feathers, or exoskeletons. Some nutrients can be metabolically converted to smaller molecules in the process of releasing energy, such as for carbohydrates, lipids, proteins, and fermentation products (ethanol or vinegar), leading to end-products of water and carbon dioxide. All organisms require water. Essential nutrients for animals are the energy sources, some of the amino acids that are combined to create proteins, a subset of fatty acids, vitamins and certain minerals. Plants require more diverse minerals absorbed through roots, plus carbon dioxide and oxygen absorbed through leaves. Fungi live on dead or living organic matter and meet nutrient needs from their host.
Different types of organism have different essential nutrients. Ascorbic acid (vitamin C) is essential, meaning it must be consumed in sufficient amounts, to humans and some other animal species, but not to all animals and not to plants, which are able to synthesize it. Nutrients may be organic or inorganic: organic compounds include most compounds containing carbon, while all other chemicals are inorganic. Inorganic nutrients include nutrients such as iron, selenium, and zinc, while organic nutrients include, among many others, energy-providing compounds and vitamins.
A classification used primarily to describe nutrient needs of animals divides nutrients into macronutrients and micronutrients. Consumed in relatively large amounts (grams or ounces), macronutrients (carbohydrates, fats, proteins, water) are used primarily to generate energy or to incorporate into tissues for growth and repair. Micronutrients are needed in smaller amounts (milligrams or micrograms); they have subtle biochemical and physiological roles in cellular processes, like vascular functions or nerve conduction. Inadequate amounts of essential nutrients, or diseases that interfere with absorption, result in a deficiency state that compromises growth, survival and reproduction. Consumer advisories for dietary nutrient intakes, such as the United States Dietary Reference Intake, are based on deficiency outcomes[clarification needed] and provide macronutrient and micronutrient guides for both lower and upper limits of intake. In many countries, macronutrients and micronutrients in significant content[clarification needed] are required by regulations to be displayed on food product labels. Nutrients in larger quantities than the body needs may have harmful effects. Edible plants also contain thousands of compounds generally called phytochemicals which have unknown effects on disease or health, including a diverse class with non-nutrient status called polyphenols, which remain poorly understood as of 2017.
Plant nutrients consist of more than a dozen minerals absorbed through roots, plus carbon dioxide and oxygen absorbed or released through leaves. All organisms obtain all their nutrients from the surrounding environment.
Plants absorb carbon, hydrogen and oxygen from air. These three, in the form of water and carbon dioxide. Other nutrients are absorbed from soil (exceptions include some parasitic or carnivorous plants). Counting these, there are 17 important nutrients for plants: the macronutrients nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), sulfur (S), magnesium (Mg), carbon (C), oxygen(O) and hydrogen (H), and the micronutrients iron (Fe), boron (B), chlorine (Cl), manganese (Mn), zinc (Zn), copper (Cu), molybdenum (Mo) and nickel (Ni). In addition to carbon, hydrogen and oxygen, nitrogen, phosphorus, and sulfur are also needed in relatively large quantities. Together, the "Big Six" are the elemental macronutrients for all organisms. They are sourced from inorganic matter (for example, carbon dioxide, water, nitrates, phosphates, sulfates, and diatomic molecules of nitrogen and, especially, oxygen) and organic matter (carbohydrates, lipids, proteins).
Macronutrients are defined in several ways.
Macronutrients provide energy:
Micronutrients support metabolism.
An essential nutrient is a nutrient required for normal physiological function that cannot be synthesized in the body – either at all or in sufficient quantities – and thus must be obtained from a dietary source. Apart from water, which is universally required for the maintenance of homeostasis in mammals, essential nutrients are indispensable for various cellular metabolic processes and maintaining tissue and organ function. In the case of humans, there are nine amino acids, two fatty acids, thirteen vitamins and fifteen minerals that are considered essential nutrients. In addition, there are several molecules that are considered conditionally essential nutrients since they are indispensable in certain developmental and pathological states.
An essential amino acid is an amino acid that is required by an organism but cannot be synthesized de novo by it, and therefore must be supplied in its diet. Out of the twenty standard protein-producing amino acids, nine cannot be endogenously synthesized by humans: phenylalanine, valine, threonine, tryptophan, methionine, leucine, isoleucine, lysine, and histidine.
Essential fatty acids (EFAs) are fatty acids that humans and other animals must ingest because the body requires them for good health but cannot synthesize them. Only two fatty acids are known to be essential for humans: alpha-linolenic acid (an omega-3 fatty acid) and linoleic acid (an omega-6 fatty acid).
Vitamins are organic molecules essential for an organism that are not classified as amino acids or fatty acids. They commonly function as enzymatic cofactors, metabolic regulators or antioxidants. Humans require thirteen vitamins in their diet, most of which are actually groups of related molecules (e.g. vitamin E includes tocopherols and tocotrienols). The list: vitamins A, C, D, E, K, Thiamine (B1), Riboflavin (B2), Niacin (B3), Pantothenic Acid (B5), Vitamin B6, Biotin (B7), Folate (B9) and Vitamin B12. The requirement for vitamin D is conditional, as people who get sufficient exposure to ultraviolet light, either from the sun or an artificial source, synthesize vitamin D in skin.
Minerals are the exogenous chemical elements indispensable for life. Although the four elements: carbon, hydrogen, oxygen, and nitrogen, are essential for life, they are so plentiful in food and drink that these are not considered nutrients and there are no recommended intakes for these as minerals. The need for nitrogen is addressed by requirements set for protein, which is composed of nitrogen-containing amino acids. Sulfur is essential, but again does not have a recommended intake. Instead, recommended intakes are identified for the sulfur-containing amino acids methionine and cysteine. There are dietary supplements which provide sulfur, such as methylsulfonylmethane.
The essential nutrient elements for humans, listed in order of Recommended Dietary Allowance (expressed as a mass), are potassium, chlorine, sodium, calcium, phosphorus, magnesium, iron, zinc, manganese, copper, iodine, chromium, molybdenum, selenium and cobalt (the last as a component of vitamin B12). There are other minerals which are essential for some plants and animals, but may or may not be essential for humans, such as boron and silicon.
Conditionally essential nutrients are certain organic molecules that can normally be synthesized by an organism, but under certain conditions in insufficient quantities. In humans, such conditions include premature birth, limited nutrient intake, rapid growth, and certain disease states. Choline, inositol, taurine, arginine, glutamine and nucleotides are classified as conditionally essential and are particularly important in neonatal diet and metabolism.
Non-essential nutrients are substances within foods that can have a significant impact on health; these substances can be beneficial or toxic.[medical citation needed] For example, dietary fiber is not absorbed in the human digestive tract, but is important in maintaining the bulk of a bowel movement to avoid constipation.[medical citation needed] A subset of dietary fiber, known as soluble fiber, can be metabolized by bacteria residing in the large intestine. Soluble fiber is marketed as serving a prebiotic function – promoting "healthy" intestinal bacteria. Bacterial metabolism of soluble fiber also produces short-chain fatty acids like butyric acid, which may be absorbed into intestinal cells as a source of calories.
By definition, phytochemicals include all nutritional and non-nutritional components of edible plants. Included as nutritional constituents are provitamin A carotenoids, whereas those without nutrient status are diverse polyphenols, flavonoids, resveratrol, and lignans – often claimed to have antioxidant effects – that are present in numerous plant foods. A number of phytochemical compounds are under preliminary research for their potential effects on human diseases and health. However, the qualification for nutrient status of compounds with poorly defined properties in vivo is that they must first be defined with a Dietary Reference Intake level to enable accurate food labeling, a condition not established for most phytochemicals that are claimed to be antioxidant nutrients.
An inadequate amount of a nutrient is a deficiency. Deficiencies can be due to a number of causes including an inadequacy in nutrient intake, called a dietary deficiency, or any of several 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 excess consumption of a nutrient does harm to an organism.
In the United States and Canada, recommended dietary intake levels of essential nutrients are based on the minimum level that "will maintain a defined level of nutriture in an individual", a definition somewhat different from that used by the World Health Organization and Food and Agriculture Organization of a "basal requirement to indicate the level of intake needed to prevent pathologically relevant and clinically detectable signs of a dietary inadequacy".
In setting human nutrient guidelines, government organizations do not necessarily agree on amounts needed to avoid deficiency or maximum amounts to avoid the risk of toxicity. For example, for vitamin C, recommended intakes range from 40 mg/day in India to 155 mg/day for the European Union. The table below shows U.S. Estimated Average Requirements (EARs) and Recommended Dietary Allowances (RDAs) for vitamins and minerals, PRIs for the European Union (same concept as RDAs), followed by what three government organizations deem to be the safe upper intake. RDAs are set higher than EARs to cover people with higher than average needs. Adequate Intakes (AIs) are set when there is not sufficient information to establish EARs and RDAs. Governments are slow to revise information of this nature. For the U.S. values, with the exception of calcium and vitamin D, all of the data date to 1997-2004.
|Nutrient||U.S. EAR||Highest U.S.
RDA or AI
PRI or AI
|α-tocopherol (Vit E)||12||15||13||1000||300||650-900||mg|
|Thiamin (Vit B1)||1.0||1.2||0.1 mg/MJ||ND||ND||ND||mg|
|Riboflavin (Vit B2)||1.1||1.3||2.0||ND||ND||ND||mg|
|Niacin* (Vit B3)||12||16||1.6 mg/MJ||35||10||60-85||mg|
|Pantothenic acid (Vit B5)||NE||5||7||ND||ND||ND||mg|
|Biotin (Vit B7)||NE||30||45||ND||ND||ND||µg|
|Folate (Vit B9)||320||400||600||1000||1000||900-1000||µg|
|Cyanocobalamin (Vit B12)||2.0||2.4||5.0||ND||ND||ND||µg|
EAR U.S. Estimated Average Requirements.
RDA U.S. Recommended Dietary Allowances; higher for adults than for children, and may be even higher for women who are pregnant or lactating.
AI U.S. Adequate Intake; AIs established when there is not sufficient information to set EARs and RDAs.
PRI Population Reference Intake is European Union equivalent of RDA; higher for adults than for children, and may be even higher for women who are pregnant or lactating. For Thiamin and Niacin the PRIs are expressed as amounts per MJ of calories consumed. MJ = megajoule = 239 food calories.
Upper Limit Tolerable upper intake levels.
ND ULs have not been determined.
NE EARs, PRIs or AIs have not yet been established or will not be (EU does not consider chromium an essential nutrient).
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