栄養素
Nutrient/ja
栄養素（えいようそ）とは、生物が生存、成長、繁殖するために用いる物質のことである。食事からの栄養素摂取の必要性は、動物、植物、真菌、原生生物に当てはまる。栄養素は代謝目的のために細胞に取り込まれたり、細胞によって分泌されたりして、毛、うろこ、羽、外骨格などの非細胞構造を作り出す。栄養素の中には、エネルギーを放出する過程で代謝的に小さな分子に変換されるものがあり、例えば炭水化物、脂質、タンパク質、発酵生成物（エタノールや酢）などがあり、最終生成物は水と二酸化炭素になる。すべての生物は水を必要とする。動物にとっての必須栄養素は、エネルギー源、タンパク質を作るために組み合わされるアミノ酸の一部、脂肪酸のサブセット、ビタミン、および特定のミネラルである。植物は、根から吸収されるより多様なミネラルと、葉から吸収される二酸化炭素と酸素を必要とする。菌類は死んだ有機物や生きている有機物の上に住み、宿主から栄養の必要性を満たす。
生物の種類によって、必須栄養素は異なる。アスコルビン酸（ビタミンC）は、ヒトや他のいくつかの動物種にとっては必須、つまり十分な量を摂取しなければならないが、一部の動物や植物は合成することができる。栄養素には有機物と無機物がある。有機化合物には炭素を含むほとんどの化合物が含まれ、それ以外の化学物質はすべて無機物である。無機栄養素には鉄、セレン、亜鉛などの栄養素が含まれ、有機栄養素にはエネルギー供給化合物やビタミンなどが含まれる。
主に動物の栄養ニーズを説明するために使用される分類では、栄養素を大栄養素と微量栄養素に分けている。比較的大量（グラムまたはオンス）に消費される大栄養素（炭水化物、脂肪、タンパク質、水）は、主にエネルギーを生成するため、または成長と修復のために組織に取り込まれるために使用される。微量栄養素は、より少量（ミリグラムまたはマイクログラム）で必要とされる。微量栄養素は、血管機能や神経伝導のような細胞プロセスにおいて、微妙な生化学および生理学的役割を担っている。必須栄養素の量が不十分であったり、吸収を妨げる疾患があると、欠乏状態に陥り、成長、生存、繁殖が損なわれる。米国の食事摂取基準のような消費者向けの食事栄養素摂取勧告は、欠乏の結果に基づいており、摂取量の下限と上限の両方について、大栄養素と微量栄養素のガイドを提供している。多くの国では、重要な含有量の大栄養素および微量栄養素は、規制により食品ラベルに表示することが義務付けられている。身体に必要な量よりも多い栄養素は、有害な影響を及ぼす可能性がある。食用植物には、一般にファイトケミカルと呼ばれる、病気や健康に未知の影響を及ぼす何千もの化合物も含まれており、その中にはポリフェノールと呼ばれる非栄養素の状態を持つ多様な分類も含まれているが、2017年時点ではまだ十分に解明されていない。
種類
大栄養素
大栄養素にはいくつかの定義がある。
- ヒトが最も大量に消費する化学元素は、炭素、水素、窒素、酸素、リン、硫黄であり、CHNOPSとして要約される。
- 人間が最も大量に消費し、大量のエネルギーを供給する化合物は、炭水化物、タンパク質、脂肪に分類される。水も大量に消費されなければならないが、カロリー価値はない。
- カルシウムイオン、ナトリウムイオン、カリウムイオン、マグネシウムイオン、塩化物イオンは、リンや硫黄とともに、微量栄養素、すなわちビタミンやその他のミネラルと比較して大量に必要とされるため、大栄養素と共に記載されている。
Macronutrients provide energy:
- Carbohydrates are compounds made up of types of sugar. Carbohydrates are classified according to 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).
- Proteins are organic compounds that consist of amino acids joined by peptide bonds. Since the body cannot manufacture some of the amino acids (termed essential 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 (saturated fatty acids) or by both double and single bonds (unsaturated fatty acids). 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 (termed essential fatty acids), they must be obtained through one's diet.
- Ethanol is not an essential nutrient, but it does provide calories.The United States Department of Agriculture uses a figure of 6.93 kilocalories (29.0 kJ) per gram of alcohol (5.47 kcal or 22.9 kJ per ml) for calculating food energy. For distilled spirits, a standard serving in the U.S. is 44 ml (1.5 US fl oz), which at 40% ethanol (80 proof) would be 14 grams and 98 calories.
| Biomolecule | Kilocalories per 1 gram | Protein | 4 |
|---|---|---|---|
| Carbohydrate | 4 | ||
| Ethanol | 7 | ||
| Fat | 9 |
Micronutrients
Micronutrients 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.
- Vitamins are organic compounds essential to the body. They usually act as coenzymes or cofactors for various proteins in the body.
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, fifteen 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 (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
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): vitamins A, C, D, E, K, thiamine (B1), riboflavin (B2), niacin (B3), pantothenic acid (B5), pyridoxine (B6), biotin (B7), folate (B9), and cobalamin (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 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 elements for humans, listed in order of Recommended Dietary Allowance (expressed as a mass), are potassium, chloride, sodium, calcium, phosphorus, magnesium, iron, zinc, manganese, copper, iodine, chromium, molybdenum, 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.
Choline
Choline is an essential nutrient. The cholines are a family of water-soluble quaternary ammonium compounds. Choline is the parent compound of the cholines class, consisting of ethanolamine having three methyl substituents attached to the amino function. Healthy humans fed artificially composed diets that are deficient in choline develop fatty liver, liver damage, and muscle damage. Choline was not initially classified as essential because the human body can produce choline in small amounts through phosphatidylcholine metabolism.
Conditionally essential
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. Inositol, taurine, arginine, glutamine and nucleotides are classified as conditionally essential and are particularly important in neonatal diet and metabolism.
Non-essential
Non-essential nutrients are substances within foods that can have a significant impact on health. Insoluble dietary fiber is not absorbed in the human digestive tract, but is important in maintaining the bulk of a bowel movement to avoid constipation. Soluble fiber can be metabolized by bacteria residing in the large intestine. Soluble fiber is marketed as serving a prebiotic function with claims for 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 food energy.
Non-nutrients
Ethanol (C2H5OH) is not an essential nutrient, but it does supply approximately 29 kilojoules (7 kilocalories) of food energy per gram. For spirits (vodka, gin, rum, etc.) a standard serving in the United States is 44 millilitres (1 1⁄2 US fluid ounces), which at 40% ethanol (80 proof) would be 14 grams and 410 kJ (98 kcal). At 50% alcohol, 17.5 g and 513 kJ (122.5 kcal). Wine and beer contain a similar amount of ethanol in servings of 150 and 350 mL (5 and 12 US fl oz), respectively, but these beverages also contribute to food energy intake from components other than ethanol. A 150 mL (5 US fl oz) serving of wine contains 420 to 540 kJ (100 to 130 kcal). A 350 mL (12 US fl oz) serving of beer contains 400 to 840 kJ (95 to 200 kcal). According to the U.S. Department of Agriculture, based on NHANES 2013–2014 surveys, women ages 20 and up consume on average 6.8 grams of alcohol per day and men consume on average 15.5 grams per day. Ignoring the non-alcohol contribution of those beverages, the average ethanol contributions to daily food energy intake are 200 and 450 kJ (48 and 108 kcal), respectively. Alcoholic beverages are considered empty calorie foods because, while providing energy, they contribute no essential nutrients.
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.
Deficiencies and toxicity
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. Countries establish tolerable upper intake levels, also referred to as upper limits (ULs), based on amounts that cause adverse effects. 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 from 1997 to 2004.
| Nutrient | U.S. EAR | Highest U.S. RDA or AI |
Highest EU PRI or AI |
Upper limit | Unit | ||
|---|---|---|---|---|---|---|---|
| U.S. | EU | Japan | |||||
| Vitamin A | 625 | 900 | 1300 | 3000 | 3000 | 2700 | µg |
| Vitamin C | 75 | 90 | 155 | 2000 | ND | ND | mg |
| Vitamin D | 10 | 15 | 15 | 100 | 100 | 100 | µg |
| Vitamin K | NE | 120 | 70 | ND | ND | ND | µg |
| 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 |
| Vitamin B6 | 1.1 | 1.3 | 1.8 | 100 | 25 | 40-60 | mg |
| Biotin (Vit B7) | NE | 30 | 45 | ND | ND | ND | µg |
| Folate (Vit B9) | 320 | 400 | 600 | 1000 | 1000 | 900-1000 | µg |
| Cobalamin (Vit B12) | 2.0 | 2.4 | 5.0 | ND | ND | ND | µg |
| Choline | NE | 550 | 520 | 3500 | ND | ND | mg |
| Calcium | 800 | 1000 | 1000 | 2500 | 2500 | 2500 | mg |
| Chloride | NE | 2300 | NE | 3600 | ND | ND | mg |
| Chromium | NE | 35 | NE | ND | ND | ND | µg |
| Copper | 700 | 900 | 1600 | 10000 | 5000 | 10000 | µg |
| Fluoride | NE | 4 | 3.4 | 10 | 7 | ____ | mg |
| Iodine | 95 | 150 | 200 | 1100 | 600 | 3000 | µg |
| Iron | 6 | 18 (females) 8 (males) |
16 (females) 11 (males) |
45 | ND | 40-45 | mg |
| Magnesium* | 350 | 420 | 350 | 350 | 250 | 350 | mg |
| Manganese | NE | 2.3 | 3.0 | 11 | ND | 11 | mg |
| Molybdenum | 34 | 45 | 65 | 2000 | 600 | 450-550 | µg |
| Phosphorus | 580 | 700 | 640 | 4000 | ND | 3000 | mg |
| Potassium | NE | 4700 | 4000 | ND | ND | 2700-3000 | mg |
| Selenium | 45 | 55 | 70 | 400 | 300 | 330-460 | µg |
| Sodium | NE | 1500 | NE | 2300 | ND | 3000-3600 | mg |
| Zinc | 9.4 | 11 | 16.3 | 40 | 25 | 35-45 | mg |
* The daily recommended amounts of niacin and magnesium are higher than the tolerable upper limit because, for both nutrients, the ULs identify the amounts which will not increase risk of adverse effects when the nutrients are consumed as a serving of a dietary supplement. Magnesium supplementation above the UL may cause diarrhea. Supplementation with niacin above the UL may cause flushing of the face and a sensation of body warmth. Each country or regional regulatory agency decides on a safety margin below when symptoms may occur, so the ULs may differ based on source.
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 megajoule (239 kilocalories) of food energy consumed.
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).
Plant
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 and soil in the form of carbon dioxide and water. Other nutrients are absorbed from soil (exceptions include some parasitic or carnivorous plants). Counting these, there are 17 important nutrients for plants: these are 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).
See also
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