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.

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. Linus Pauling said of vitamin B3 (either niacin or niacinamide): "What astonished me was the very low toxicity of a substance that has such very great physiological power. A little pinch, 5 mg, every day, is enough to keep a person from dying of pellagra, but it is so lacking in toxicity that ten thousand times as much can [sometimes] be taken without harm."

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


 * α-Linolenic acid (ALA, 18:3), an omega-3 fatty acid
 * Linoleic acid (LA, 18:2), an omega-6 fatty acid

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).

Omega-9 fatty acids are not essential in humans, because humans generally possess all the enzymes required for their synthesis.

Amino acids

 * Isoleucine
 * Lysine
 * Leucine
 * Methionine
 * Phenylalanine
 * Threonine
 * Tryptophan
 * Valine
 * Histidine
 * Arginine

Carbohydrates
Carbohydrates are sugar molecules and chains of sugar molecules. No individual carbohydrate is an essential nutrient in humans. Glucose can be synthesized from amino acids and glycerol, which is obtained from fat metabolism, by de novo synthesis (called gluconeogenesis), but in insufficient quantities to maintain normal brain metabolism. 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.

Vitamins

 * Vitamin A (beta-carotene,retinol)
 * Vitamin B1 (thiamin)
 * Vitamin B2 (riboflavin, vitamin G)
 * Vitamin B3 (niacin, vitamin P, vitamin PP)
 * Vitamin B5 (pantothenic acid)
 * Vitamin B6 (pyridoxine, pyridoxamine, or pyridoxal)
 * Vitamin B7 (biotin, vitamin H)
 * Vitamin B9 (folic acid, folate, vitamin M)
 * Vitamin B12 (cobalamin)
 * Vitamin C (ascorbic acid)
 * Vitamin D (ergocalciferol, or cholecalciferol)
 * Vitamin E (tocopherol)
 * Vitamin K (naphthoquinoids)

Dietary minerals

 * Calcium (Ca)
 * Chloride (Cl&minus;)
 * Chromium (Cr)
 * Cobalt (Co) (as part of Vitamin B12)
 * Copper (Cu)
 * Iodine (I)
 * Iron (Fe)
 * Magnesium (Mg)
 * Manganese (Mn)
 * Molybdenum (Mo)
 * Phosphorus (P)
 * Potassium (K)
 * Selenium (Se)
 * Sodium (Na)
 * Zinc (Zn)

The required quantity varies widely between nutrients. At extremes, a 70 kg human contains 1.0 kg of calcium, but only 3 mg of cobalt.

Other

 * Choline