Nutrition is the science of food and its relationship to health. Nutrients are the building blocks of the human body. They are chemicals in foods that are used by the body for growth, maintenance, disease prevention, health restoration, and energy. Nutrients that cannot be synthesized by the body and thus must be derived from the diet are considered essential. They include carbohydrates, fats (lipids), minerals (macro minerals, micro minerals, trace elements), proteins, vitamins, and water. Nutrients that the body can synthesize from other compounds, although they may also be derived from the diet, are considered nonessential. Macronutrients are required by the body in relatively large amounts; micronutrients are needed in minute amounts.

Lack of nutrients (nutritional deficiency) can result in deficiency syndromes (eg, kwashiorkor, marasmus, depression, irritability, confusion, pellagra, scurvy, immune deficiency, osteoporosis, diabetes, rickets, beriberi, goiter, insomnia, anxiety, mood disorders, anaemia, retardation, cancer... ) or other disorders. Excess intake of macronutrients can lead to obesity and related disorders; excess intake of micronutrients can be toxic. Also, the balance of various types of nutrients, such as how much unsaturated vs saturated fat is consumed, can influence the development of disorders.

Macronutrients

Macronutrients constitute the bulk of the diet and supply energy and many essential nutrients. Carbohydrates, proteins(including essential amino acids), fats (including essential fatty acids), macrominerals, and water are macronutrients. Carbohydrates, fats, and proteins are interchangeable as sources of energy; fats yield 9 kcal/g (37.8 kJ/g); proteins and carbohydrates yield 4 kcal/g (16.8 kJ/g).

Carbohydrates:
Dietary carbohydrates are broken down into glucose and other monosaccharides. Carbohydrates increase plasma glucose levels, supplying energy. Simple carbohydrates are composed of small molecules, generally monosaccharides or disaccharides, which increase plasma glucose levels rapidly. Complex carbohydrates are composed of larger molecules, which are broken down into monosaccharides. Complex carbohydrates increase plasma glucose levels more slowly but for a longer time. Glucose and sucrose are simple carbohydrates; starches and fiber are complex carbohydrates.

The glycemic index measures how rapidly consumption of a carbohydrate increases plasma glucose levels. Values range from 1 (the slowest increase) to 100 (the fastest increase, equivalent to pure glucose. However, the actual rate of increase also depends on what foods are consumed with the carbohydrate.

Table 1

Glycemic Index of Some Foods
Category	Food	Index*
Beans	Kidney	33
	Red lentils	27
	Soy	14
Bread	Pumpernickel	49
	White	69
	Whole wheat	72
Cereals	All bran	54
	Corn flakes	83
	Oatmeal	53
	Puffed rice	90
	Shredded wheat	70
Dairy	Milk, ice cream, yogurt	34–38
Fruit	Apple	38
	Banana	61
	Orange	43
	Orange juice	49
	Strawberries	32
Grains	Barley	22
	Brown rice	66
	White rice	72
Pasta	—	38
Potatoes	Instant mashed (white)	86
	Mashed (white)	72
	Sweet	50
Snacks	Corn chips	72
	Oatmeal cookies	57
	Potato chips	56
Sugar	Fructose	22
	Glucose	100
	Honey	91
	Refined sugar	64
*Values may vary.

Carbohydrates with a high glycemic index may increase plasma glucose to high levels rapidly. It is hypothesized that, as a result, insulin levels increase, inducing hypoglycemia and hunger, which tends to lead to consumption of excess calories and weight gain. Carbohydrates with a low glycemic index increase plasma glucose levels slowly, resulting in lower postprandial insulin levels and less hunger, which probably makes consumption of excess calories less likely. These effects are predicted to result in a more favorable lipid profile and a decreased risk of obesity, diabetes mellitus, and complications of diabetes if present.

Proteins:
Dietary proteins are broken down into peptides and amino acids. Proteins are required for tissue maintenance, replacement, function, and growth. However, if the body is not getting enough calories from dietary sources or tissue stores (particularly of fat), protein may be used for energy.

As the body uses dietary protein for tissue production, there is a net gain of protein (positive nitrogen balance).
During catabolic states (eg, starvation, infections, burns), more protein may be used (because body tissues are broken down) than is absorbed, resulting in a net loss of protein (negative nitrogen balance). Nitrogen balance is best determined by subtracting the amount of nitrogen excreted in urine and feces from the amount of nitrogen consumed.

Of the 20 amino acids, 9 are essential amino acids (EAAs); they cannot be synthesized and must be obtained from the diet. All people require 8 EAAs; infants also require histidine.

The weight-adjusted requirement for dietary protein correlates with growth rate, which decreases from infancy until adulthood. The daily dietary protein requirement decreases from 2.2 g/kg in 3-mo-old infants to 1.2 g/kg in 5-yr-old children and to 0.8 g/kg in adults. Protein requirements correspond to EAA requirements. Adults trying to increase muscle mass need very little extra protein beyond the requirements in the table.

Table 2

Essential Amino Acid Requirements in mg/kg Body Weight
Requirement	Infant (4–6 mo)	Child (10–12 yr)	Adult
Histidine	29	—	—
Isoleucine	88	28	10
Leucine	150	44	14
Lysine	99	49	12
Methionine and cystine	72	24	13
Phenylalanine and tyrosine	120	24	14
Threonine	74	30	7
Tryptophan	19	4	3
Valine	93	28	13
Total essential amino acids (excluding histidine)	715	231	86

The amino acid composition of protein varies widely. Biological value (BV) reflects the similarity in amino acid composition of protein to that of animal tissues; thus, BV indicates what percentage of a dietary protein provides EAAs for the body. A perfect match is egg protein, with a value of 100. Animal proteins in milk and meat have a high BV (~90); proteins in cereal and vegetables have a lower BV (~40), and some derived proteins (eg, gelatin) have a BV of 0. The extent to which dietary proteins supply each other's missing amino acids (complementarity) determines the overall BV of the diet. The recommended daily allowances (RDA) for protein assumes that the average mixed diet has a BV of 70.

Fats:
Fats are broken down into fatty acids and glycerol. Fats are required for tissue growth and hormone production. Saturated fatty acids, common in animal fats, tend to be solid at room temperature. Except for palm and coconut oil, fats
derived from plants tend to be liquid at room temperature; these fats contain high levels of monounsaturated fatty acids or polyunsaturated fatty acids (PUFAs).

Partial hydrogenation of unsaturated fatty acids (as occurs during food manufacturing) produces trans fatty acids, which are solid or semisolid at room temperature. In the US, the main dietary source of trans fatty acids is partially hydrogenated vegetable oils, used in manufacturing certain foods (eg, cookies, crackers, chips) to prolong shelf-life. Trans fatty acids may elevate LDL cholesterol and lower HDL; they may also independently increase the risk of coronary
artery disease.

Essential fatty acids (EFAs) are linoleic acid, an ?-6 (n-6) fatty acid, and linolenic acid, an ?-3 (n-3) fatty acid. Other ?-6 acids (eg, arachidonic acid) and other ?-3 fatty acids (eg, eicosapentaenoic acid, docosahexaenoic acid) are required by the body but can be synthesized from EFAs.

EFAs are needed for the formation of various eicosanoids (biologically active lipids), including prostaglandins,
thromboxanes, prostacyclins, and leukotrienes. Consumption of ?-3 fatty acids may decrease the risk of coronary artery disease.

Requirements for EFAs vary by age. Adults require amounts of linoleic acid equal to at least 2% of total caloric needs
and linolenic acid equal to at least 0.5%. Vegetable oils provide linoleic acid and linolenic acid. Oils made from safflower, sunflower, corn, soya, primrose, pumpkin, and wheat germ provide large amounts of linoleic acid. Marine fish oils and oils made from flaxseeds, pumpkin, soy, and canola provide large amounts of linolenic acid. Marine fish
oils also provide some other ?-3 fatty acids in large amounts.

Macrominerals:
Na, Cl, K, Ca, P, and Mg are required in relatively large amounts per day.

Table 3

Macrominerals
Nutrient	Principal Sources	Functions
Ca	Milk and milk products, meat, fish, eggs, cereals, beans, fruits, vegetables	Bone and tooth formation, blood coagulation, neuromuscular irritability, muscle contractility, myocardial conduction
Cl	Many foods, mainly animal products but some vegetables; similar to Na	Acid-base balance, osmotic pressure, blood pH, kidney function
K	Many foods, including whole and skim milk, bananas, prunes, raisins, meats	Muscle activity, nerve transmission, intracellular acid-base balance, water retention
Mg	Green leaves, nuts, cereals, grains, seafood	Bone and tooth formation, nerve conduction, muscle contraction, enzyme activation
Na	Many foods, including beef, pork, sardines, cheese, green olives, corn bread, potato chips, sauerkraut	Acid-base balance, osmotic pressure, blood pH, muscle contractility, nerve transmission, maintenance of cell membrane gradients
P	Milk, cheese, meat, poultry, fish, cereals, nuts, legumes	Bone and tooth formation, acid-base balance, energy production

Table 4

Recommended Dietary References Intakes* for Some Macronutrients, Food and Nutrition Board, Institute of Medicine of the National Academies
Category	Age or Time Frame (yr)	Protein (g/kg)	Energy(kcal/kg)	Calcium (mg/kg)	Phosphorus (mg/kg)	Magnesium (mg/kg)
Infants	0.0–0.5	2.2	108.3	66.7	50.0	6.7
	0.5–1.0	1.6	94.4	66.7	55.6	6.7
Children	1–3	1.2	100.0	61.5	61.5	6.2
	4–6	1.2	90.0	40.0	40.0	6.0
	7–10	1.0	71.4	28.6	28.6	6.1
Males	11–14	1.0	55.6	26.7	26.7	6.0
	15–18	0.9	45.5	18.2	18.2	6.1
	19–24	0.8	40.3	16.7	16.7	4.9
	25–50	0.8	36.7	10.1	10.1	4.4
	51+	0.8	29.9	10.4	10.4	4.5
Females	11–14	1.0	47.8	26.1	26.1	6.1
	15–18	0.8	40.0	21.8	21.8	5.5
	19–24	0.8	37.9	20.7	20.7	4.8
	25–50	0.8	34.9	12.7	12.7	4.4
	51+	0.8	29.2	12.3	12.3	4.3
Pregnant		0.9	4.6	18.5	18.5	4.9
Breastfeeding	1st yr	1.0	7.9	19.0	19.0	5.4
*These amounts, expressed as average daily intakes over time, are intended to provide for individual variations among most healthy people living in the US under usual environmental stresses.

>Water:
Water is considered a macronutrient because it is required in amounts of 1 mL/kcal (0.24 mL/kJ) of energy expended, or about 2500 mL/day. Needs vary with fever, physical activity, and changes in climate and humidity.

Micronutrients

Vitamins and minerals required in minute amounts (trace minerals) are micronutrients.

Water-soluble
vitamins are vitamin C (ascorbic acid) and 8 members of the vitamin B complex: biotin, folate, niacin, pantothenic
acid, riboflavin (vitamin B₂), thiamin (vitamin B₁), vitamin B₆ (pyridoxine), and vitamin B₁₂(cobalamin).

Fat-soluble
vitamins are vitamins A (retinol), D (cholecalciferol and ergocalciferol), E (?-tocopherol), and K (phylloquinone and menaquinone).

Only vitamins A, E, and B₁₂ are stored to any significant extent in the body; the other vitamins must be consumed regularly to maintain tissue health.

Essential
trace minerals include chromium, copper, iodine, iron, manganese, molybdenum, selenium, and zinc. Except for chromium, each of these is incorporated into enzymes or hormones required in metabolism. Except for deficiencies of iron and zinc, micromineral deficiencies are uncommon in developed countries.

Other minerals (eg, aluminum, arsenic, boron, cobalt, fluoride, nickel, silicon, vanadium) have not been proved essential for people. Fluoride, although not essential, helps prevent tooth decay by forming a compound with Ca (CaF₂), which stabilizes the mineral matrix in teeth.

All trace minerals are toxic at high levels, and some (arsenic, nickel, and chromium) may cause cancer.

Other
Dietary Substances

The daily human diet typically contains as many as 100,000 chemicals (eg, coffee contains 1000). Of these, only 300 are
nutrients, only some of which are essential. However, many nonnutrients in foods are useful. For example, food additives (eg, preservatives, emulsifiers, antioxidants, stabilizers) improve the production and stability of foods. Trace components (eg, spices, flavors, odors, colors, phytochemicals, many other natural products) improve appearance and taste.

Fiber:
Fiber occurs in various forms (eg, cellulose, hemicellulose, pectin, gums). It increases GI motility, prevents constipation, and helps control diverticular disease. Fiber is thought to accelerate the elimination of cancer-causing substances produced by bacteria in the large intestine. Epidemiologic evidence suggests an association between colon cancer and low fiber intake and a beneficial effect of fiber in patients with functional bowel disorders, Crohn's disease, obesity, and hemorrhoids. Soluble fiber (present in fruits, vegetables, oats, barley, and legumes) reduces the postprandial increase in plasma glucose and insulin and can reduce cholesterol levels.

The typical Western diet is low in fiber (about 12 g/day) because of a high intake of highly refined wheat flour and a low
intake of fruits and vegetables. Increasing fiber intake to about 30 g/day by consuming more vegetables, fruits, and high-fiber cereals and grains is generally recommended. However, very high fiber intake may reduce absorption of certain minerals.

Last full review/revision July 2007 by Margaret-Mary G. Wilson, MD

Nutrients: Part II

Nutrients are essential dietary factors such as water, vitamins, proteins, carbohydrates, fatty acids, minerals (macro-minerals and micro-minerals).

Nutrition is the study of nutrients—water, carbohydrates, proteins, fats, vitamins and minerals—that are essential for life. Nutrition students learn how these nutrients are ingested, digested, absorbed, metabolized, stored and excreted. Nutrition also involves the study of food availability and how the nutrition choices we make can affect our health.

Food and Fitness: Nutrient

A nutrient is a substance present in food and used by the body to promote normal growth, maintenance, and repair. The major nutrients needed to maintain health are carbohydrates, fats, proteins, minerals, vitamins, and water. Nutrients are used in an organism's metabolism which must be taken in from the environment. Non-autotrophic organisms typically acquire nutrients by the ingestion of foods. Methods for nutrient intake vary, with animals and protists having an internal digestive system, while plants digest nutrients externally and then ingested.

Organic and Inorganic

Organic nutrients include carbohydrates, fats, proteins (or their building blocks, amino acids), and vitamins.

Inorganic chemical compounds such as minerals; water and oxygen may also be considered nutrients. A nutrient is essential to an organism if it cannot be synthesized by the organism in sufficient quantities and must be obtained from an external source. Nutrients needed in relatively large quantities are called macronutrients and those needed in relatively small quantities are called micronutrients.

Macronutrients are defined in several different ways.

* The chemical elements humans consume in the largest quantities are carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur.

* 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 relatively large quantities compared to other vitamins and minerals. They are sometimes referred to as the macrominerals.

The remaining vitamins, minerals, or elements, are called micronutrients because they are required in relatively small quantities.

Substances that provide energy

* Carbohydrates are compounds made up 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).

* Proteins are organic compounds that consists of the amino acids joined by peptide bonds. The body cannot manufacture some of the amino acids (termed essential amino acids); the diet must supply these. In nutrition, proteins are broken down through digestion by proteases back into free amino acids.

* Fats consist of a glycerin molecule with three fatty acids attached. Fatty acids are unbranched hydrocarbon chains, connected by single bonds alone (saturated fatty acids) or by both double and single bonds (unsaturated fatty acids). Fats are needed to keep cell membranes functioning properly, to insulate body organs against shock, to keep body temperature stable, and to maintain healthy skin and hair. The body does not manufacture certain fatty acids (termed essential fatty acids) and the diet must supply these.

Fat has an energy content of 9 kcal/g (~37.7 kJ/g); proteins and carbohydrates 4 kcal/g (~16.7 kJ/g). Ethanol (grain alcohol) has an energy content of 7 kcal/g (~29.3 kJ/g).

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.

* Vitamins are organic compounds essential to the body. They usually act as 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.

Food & Culture Encyclopedia: Nutrients

Nutrients are those organic and inorganic compounds that a living organism must acquire from the environment to support essential life processes, including basal metabolism, growth and maintenance of body tissues, activity, reproduction, and maintenance of general health. Nutrients are normally obtained by the ingestion of foods. Organic nutrients include carbohydrates, proteins or amino acids, lipids, and vitamins. Inorganic nutrients include minerals.

Nutrients are essential to life and cannot be subjected to safety analyses like environmental toxins or synthetic drugs. Virtually all research published in mainstream journals is focused on how essential nutrients heal organisms on the cellular level, which nutrients act together to bring about organ repair, and how they cause systemic healing when given in very high doses. Science has known for at least a century that deficiencies cause standard diseases. In the presence of certain viruses and environmental toxins, such deficiencies are major contributing factor to AIDS and all cancers. Indeed, the South Africans recently renamed AIDS to NAIDS which stands for "Nutritionally Acquired Immune Deficiency Syndrome" because recent research showed that for the HIV virus to cause illness, a person must also be deficient in the immune-system-controlling mineral Selenium (Foster 2004).

Classification of Nutrients

Nutrients often are classified as essential or nonessential. Essential nutrients are those that cannot be synthesized in the body at all or in sufficient amounts to meet needs and, thus, must be obtained preformed in the diet. These include the essential (indispensable) amino acids, the essential fatty acids, the vitamins, and the minerals. Two amino acids are classified as semi-essential because, although they can be synthesized in sufficient quantities in the body, their synthesis depends upon a supply of an essential amino acid. Other nutrients are considered conditionally essential, meaning that they are not normally required by a healthy adult but may be required in certain disease states or at certain stages of life because of increased demand or impaired synthesis. Nonessential nutrients include those that are oxidized as fuels and those that provide carbon skeletons and amino groups for endogenous synthesis of body constituents. The term "dispensable" is sometimes used to describe these nutrients, as the nutrients are not truly nonessential: an adequate amount of carbohydrate, protein, and fat must be taken in to supply the substrates required for maintenance of blood glucose, as fuel for oxidative metabolism and synthesis of ATP, and as substrate for synthesis of body components. They are "nonessential" only in the sense that carbohydrate, fat, or protein, as well as ethanol, can be used as fuels; in that either carbohydrate or protein or even the glycerol backbone of triacylglycerols (fat) can be a source of glucose; in that any fuel potentially can be used for synthesis of most lipids; and in that amino groups from most amino acids can be used for synthesis of indispensable amino acids. Also, some food components that have health benefits and are considered important parts of healthy diets, such as fiber and phytochemicals, are not required and are not considered nutrients per se.

Essential and non-essential nutrients

Nutrients are frequently categorized as essential or nonessential. Essential nutrients are unable to be synthesized internally (either at all, or in sufficient quantities), and so must be consumed by an organism from its environment.

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.

Humans can derive energy from a wide variety of fats, carbohydrates, proteins, and ethanol, and can synthesize other needed amnio acids from the essential nutrients.

Non-essential nutrients 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 nutrients which may have health benefits.

The following table summarizes the nutrient classes, the essential compounds in each class, and the basic functions of these nutrients in the body.

Summary of Nutrients and Their Functions

Nutrient class	Essential compounds in class	Function in body
Carbohydrates (composed of glucose, galactose, fructose, and other sugars)	None	Fuel—oxidation or storage as glycogen;
		Source of carbon skeletons for synthesis of various organic compounds
Proteins (composed of amino acids)	Histidine	Protein synthesis;
	Isoleucine	Substrate for synthesis of essential nonprotein compounds;
	Leucine
	Lysine	Source of amino groups for synthesis of nonessential amino acids;
	Methionine (and Cysteine)
	Phenylalanine (and Tyrosine)	Source of carbon skeletons for synthesis of various organic compounds including glucose and nonessential amino acids;
	Threonine
	Tryptophan
	Valine	Fuel—oxidation or conversion to carbohydrate or fat for storage
	Sufficient total amino acids to supply amino groups for synthesis of nonessential amino acids
Lipids	n-6 Essential fatty acids (e.g., linoleic acid)	Fuel—oxidation or storage;
	n-3 Essential fatty acids (e.g., α-linolenic acid)	Carbon skeletons for synthesis of various organic compounds in body;
	Sufficient dietary lipids to ensure adequate absorption of fat-soluble vitamins	Polyunsaturated (n-6 and n-3) fatty acids are required for synthesis of eicosanoids, inositol phosphoglycerides, sphingolipids, and membrane phospholipids
Vitamins
B vitamins	Niacin	Synthesis of coenzymes NAD(H) and NADP(H) that participate in oxidation-reduction reactions;
		Substrate for ADP-ribosylation of macromolecules
	Thiamin	Synthesis of coenzyme thiamin pyrophosphate (TPP) that is required by transketolase and α-ketoacid dehydrogenase complexes
	Riboflavin	Synthesis of coenzymes FAD and FMN that participate in oxidation-reduction reactions
	Vitamin B₁₂	Synthesis of coenzymes deoxyadenosylcobalamin and methylcobalamin that participate in the metabolism of methionine and of propionyl/methylmalonyl CoA, respectively
	Folate	Synthesis of folate coenzymes, including tetrahydrofolate, methyl-tetrahydrofolate, methylene-tetrahydrofolate, and 10-formyl-tetrahydrofolate; the coenzymes are required for the metabolism of glycine, serine, methionine, and histidine, and the synthesis of purines and dTMP
	Vitamin B₆	Synthesis of coenzymes pyridoxal 5'-phosphate (PLP) and pyridoximine 5'-phosphate (PMP) that are involved in amino acid metabolism
	Pantothenic Acid	Synthesis of coenzyme A;
		Synthesis of acyl carrier protein domain of fatty acid synthase
	Biotin	Coenzyme for synthesis of holocarboxylases
Other Vitamins
	Vitamin C	Electron donor for enzymatic and nonenzymatic reactions
	Vitamin A	Precursor of 11-cis-retinal required for visual function;
		Precursor of all-trans retinoic acid and other metabolites that bind retinoid nuclear receptors
	Vitamin D	Precursor of vitamin D hormone
	Vitamin E	Lipid-soluble antioxidant
	Vitamin K	Substrate for γ-glutamylcarboxylase
Minerals
Macroelements	Calcium	Regulation of cellular activities by intracellular Ca²⁺ (2^d messenger function);
		Activation of certain proteins;
		Effects on excitability of nerve and muscle tissues;
		Component of mineralized tissue
	Phosphorus	Substrate for synthesis of nucleotides, DNA and RNA, phospholipids, signaling molecules, creatine phosphate, and other phosphoesters;
		Regulation of protein function via phosphorylation of tyrosyl, seryl, or threonyl residues of proteins;
		Substrate for oxidative phosphorylation (ATP synthesis);
		Component of mineralized tissue;
		Acid-base buffer system
	Magnesium	Anion charge neutralization (e.g., Mg^2+.ATP^4-);
		Essential for function of certain proteins;
		Stabilization of DNA and RNA structures
	Sodium	Membrane potentials of all cells and excitability of nerve and muscle tissues;
		Major extracellular cation;
		Generation and maintenance of electrical and osmotic gradients;
		Nutrient transport
	Potassium	Major intracellular cation;
		Membrane potential and excitability of nerve and muscle tissues
	Chloride	Major inorganic anion in body fluids
	(Sulfur)	Not essential as sulfur because sufficient inorganic sulfur is formed from catabolism of methionine and cysteine;
		Synthesis of Fe-S cluster proteins, various sulfoesters, including those in glycosaminoglycans
Microelements
	Iron	Synthesis of heme proteins, iron-sulfur cluster proteins, Fe-containing metalloenzymes
	Zinc	Conformation of zinc-finger proteins;
		Metalloenzymes—catalytic and noncatalytic roles
	Copper	Metalloenzymes—catalytic role
	Manganese	Metalloenzymes—catalytic and regulatory roles
	Iodine	Synthesis of thyroid hormone
	Molybdenum	Synthesis of Mo-containing coenyzme
	Selenium	Synthesis of selenocysteinyl residues of selenoproteins
	Boron and Chromium?	Probably are essential
	Nickel, Vanadium, Silicon, Arsenic, and Fluorine?	Possibly are essential
		(Although fluorine is not known to be nutritionally essential, its health benefits in prevention of dental caries are significant and fluoride intake, mainly from water, is recommended.)
	(Cobalt)	Vitamin B₁₂ contains cobalt, but inorganic cobalt is not required