Nutrient
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 into smaller molecules in the process of releasing energy such as for carbohydrates, lipids, proteins and fermentation products 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 organisms have different essential nutrients. Ascorbic acid is essential to humans and some animal species but most other animals and many plants 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, protein, fats, sugars and vitamins.
A classification used primarily to describe nutrient needs of animals divides nutrients into macronutrients and micronutrients. Consumed in relatively large amounts, macronutrients are primarily used to generate energy or to incorporate into tissues for growth and repair. Micronutrients are needed in smaller amounts ; 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 the amount required to prevent deficiency and provide macronutrient and micronutrient guides for both lower and upper limits of intake. In many countries, regulations require that food product labels display information about the amount of any macronutrients and micronutrients present in the food in significant quantities. 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 2024.
Types
Macronutrients
Macronutrients are defined in several ways.- The chemical elements humans consume in the largest quantities are carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulphur, summarized as CHNOPS.
- The chemical compounds that humans consume in the largest quantities and provide bulk energy are classified as carbohydrates, proteins, and fats. Water must be also consumed in large quantities but does not provide caloric value.
- Calcium, sodium, potassium, magnesium, and chloride ions, along with phosphorus and sulfur, are listed with macronutrients because they are required in large quantities compared to micronutrients, i.e., vitamins and other minerals, the latter often described as trace or ultratrace minerals.
- Carbohydrates are compounds made up of types of sugar. Carbohydrates are classified according to their number of sugar units: monosaccharides, disaccharides, oligosaccharides, and polysaccharides.
- Proteins are organic compounds that consist of amino acids joined by peptide bonds. Since the body cannot manufacture some of the amino acids, the diet must supply them. Through digestion, proteins are broken down by proteases back into free amino acids.
- Fats consist of a glycerin molecule with three fatty acids attached. Fatty acid molecules contain a -COOH group attached to unbranched hydrocarbon chains connected by single bonds alone or by both double and single bonds. Fats are needed for construction and maintenance of cell membranes, to maintain a stable body temperature, and to sustain the health of skin and hair. Because the body does not manufacture certain fatty acids, they must be obtained through one's diet.
| Biomolecule | Kilocalories per 1 gram |
| Protein | 4 |
| Carbohydrate | 4 |
| Ethanol | 7 |
| Fat | 9 |
Micronutrients
are essential dietary elements required in varying quantities throughout life to serve metabolic and physiological functions.- Dietary minerals, such as potassium, sodium, and iron, are elements native to Earth, and cannot be synthesized. They are required in the diet in microgram or milligram amounts. As plants obtain minerals from the soil, dietary minerals derive directly from plants consumed or indirectly from edible animal sources.
- Vitamins are organic compounds required in microgram or milligram amounts. The importance of each dietary vitamin was first established when it was determined that a disease would develop if that vitamin was absent from the diet.
Essentiality
Essential nutrients
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 for the maintenance and function of tissues and organs. The nutrients considered essential for humans comprise nine amino acids, two fatty acids, thirteen vitamins, fourteen minerals and choline. In addition, there are several molecules that are considered conditionally essential nutrients since they are indispensable in certain developmental and pathological states.Amino acids
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.Fatty acids
Essential fatty acids 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 and linoleic acid.Vitamins and vitamers
Vitamins occur in a variety of related forms known as vitamers. The vitamers of a given vitamin perform the functions of that vitamin and prevent symptoms of deficiency of that vitamin. Vitamins are those essential organic molecules 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 : vitamins A, C, D, E, K, thiamine, riboflavin, niacin, pantothenic acid, pyridoxine, biotin, folate, and cobalamin. 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 the skin.Minerals
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.The essential nutrient trace elements for humans, listed in order of recommended dietary allowance, are potassium, chloride, sodium, calcium, phosphorus, magnesium, iron, zinc, manganese, copper, iodine, chromium, molybdenum, and selenium. Additionally, cobalt is a component of vitamin B12 which is essential. 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.