The actual list — nine amino acids, two fatty acids, thirteen vitamins, around fifteen minerals, water — and what the word “essential” is doing when a label uses it.
~13 min read
A body builds almost everything it is made of. Every protein in your muscle, every enzyme in your liver, the cholesterol in your cell membranes — assembled inside you, from parts. There is a short list of things it cannot assemble, and that list is what the word essential names.
A nutrient is essential when the body cannot make it, or cannot make enough, so it must arrive from outside. That is a statement about where a substance comes from, not about how important it is. Remove it and a specific, repeatable deficit appears; put it back and it resolves. Counted out: nine amino acids, two fatty acids, thirteen vitamins, around fifteen minerals, and water.
Essential
Cannot be made, or not in enough quantity. Around forty substances qualify.
Conditionally essential
Normally made in enough quantity, but production falls behind demand under growth, recovery or age.
Non-essential
The body makes it. A statement about manufacture, not importance: cholesterol is non-essential and you would die without it.
Diagram to come
The whole essential list on one page as a single inventory grid, so the reader can see how short it is. Five labelled blocks sized in proportion to their item counts: 9 amino acids, 2 fatty acids, 13 vitamins, ~15 minerals, 1 water. Each block shows its items as small cells rather than as text — the visual point is the countability. Around the grid, a thin outer ring holding non-essential-but-required examples (cholesterol, glucose, glutathione, CoQ10) drawn in a lighter weight and clearly OUTSIDE the grid, and a second faint ring beyond that labelled phytonutrients with no count at all.
Non-essential does damage as a word, because it sounds like optional and never means it. Glucose is non-essential in the dietary sense and your brain runs on it. CoQ10 sits inside the machinery that makes energy, and L-carnitine carries fat into a mitochondrion to be burned.
Vitamin D is the strangest entry. Skin holds a cholesterol derivative, 7-dehydrocholesterol, which ultraviolet B light converts directly into vitamin D — so a body with enough sun makes its own, and the substance is closer to a hormone the skin manufactures. Niacin can be built from tryptophan, at sixty milligrams to one. Choline was on no essential list until 1998, when it was added after work showed that people fed a diet without it developed measurable problems even though the body makes some. The list describes human biochemistry as currently understood, not a fixed inventory — and conditionally essential applies the same idea to one person rather than the species. Arginine, glutamine, cysteine and glycine are all made internally, and all can fall behind demand.
Protein, fat and carbohydrate are macronutrients because of the quantity: they arrive in grams and tens of grams, where a vitamin arrives in milligrams or micrograms. All three supply energy. Only two supply something the body cannot otherwise obtain.
Protein — structure and machinery
Twenty amino acids build every protein in a human body, nine of them essential: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine. Protein is not mainly fuel — it is collagen, the actin and myosin that contract, every enzyme and antibody.
Fat — membranes, signalling, transport
Every cell is wrapped in a double layer of fat — also raw material for the steroid hormones, and the only vehicle in which vitamins A, D, E and K travel. Nine kilocalories a gram against four.
Carbohydrate — fuel, and the company it keeps
The brain alone runs through roughly 120 grams of glucose a day at rest. No carbohydrate is individually essential: the liver builds glucose from amino acids and from the glycerol of fat.
The protein number worth carrying is turnover. An adult body dismantles and rebuilds somewhere near 250 to 300 grams of protein a day — far more than anyone eats — because most amino acids are recycled from tissue taken apart. Protein has no storage depot: after a small circulating pool, the body takes what it needs from working tissue. Protein and greens covers what adequate looks like.
A true fact that is constantly misused
There is no essential carbohydrate. Correct biochemistry, and a statement about survival rather than about a good diet. Gluconeogenesis runs on amino acids, so when carbohydrate is absent and protein is short, the substrate comes out of your own tissue. And those foods carry most of the fibre, potassium, folate and vitamin C in a normal diet.
A vitamin is an organic compound the body requires in small amounts and cannot produce in sufficient quantity. Thirteen substances meet that definition for humans. The gaps in the B numbering are that definition being enforced: B4, B8 and B10 were named, studied and struck off.
What survived splits by one physical property — whether the molecule dissolves in fat or in water — and that decides how it is absorbed, how long it stays, and whether a large amount carries any risk.
| Fat-soluble | Needed for | Found in |
|---|---|---|
| A | Normal vision; skin, and the linings of airways and gut | Liver, egg yolk; beta-carotene in carrots |
| D | Calcium absorption, and normal bone and teeth | Oily fish, egg yolk; made in skin under UVB |
| E | Protecting membrane fats from oxidation | Nuts, seeds, wheatgerm |
| K | Clotting proteins, and those that bind calcium into bone | Leafy greens; fermented foods |
| Water-soluble | Needed for | Found in |
|---|---|---|
| C | Collagen; taking up iron from plants | Citrus, peppers, berries |
| B1 Thiamin | Energy from carbohydrate; nerve function | Whole grains, pork, legumes |
| B2 Riboflavin | Energy metabolism; skin and eyes | Dairy, eggs, almonds |
| B3 Niacin | The carriers hundreds of reactions use | Meat, fish, peanuts |
| B5 Pantothenic acid | Coenzyme A — the hub of every fuel pathway | Almost everything — the name means “from everywhere” |
| B6 | Amino acids, neurotransmitters, haemoglobin | Fish, poultry, chickpeas |
| B7 Biotin | Fat and carbohydrate metabolism; hair and nails | Egg yolk, nuts, seeds |
| B9 Folate | Making DNA, and cell division | Leafy greens, legumes, liver |
| B12 | Nerve sheaths, red cells, methylation | Animal and fortified foods only |
Two rows carry weight beyond the others. Vitamin B12 is absent from plant foods, and absorbing it needs a protein from the stomach lining and a receptor at the far end of the small intestine — a route that thins with age. Vitamin D is the one most people at high latitudes make less of than their physiology expects.
Water-soluble vitamins travel dissolved in the water compartment, and there is nowhere to put a surplus — the kidney filters the excess and it leaves within hours. Fat-soluble vitamins dissolve in fat, and a body has a great deal of fat to dissolve them in, so A and D are held in the liver and E in adipose tissue, with stores that can hold months. That is why tolerable upper intake levels exist for preformed vitamin A and for vitamin D — not because they are dangerous, but because the ceiling is reachable. It is also why they need a meal: a fat-soluble vitamin must be packaged into a bile-coated droplet called a micelle, and bile is released only when fat arrives in the small intestine. Take A, D, E and K with food that contains some fat.
Every one of the thirteen was found by subtraction. James Lind divided twelve sailors with scurvy into six pairs in 1747, giving each pair a different remedy; the pair given oranges and lemons recovered. Christiaan Eijkman later found the same shape of answer in chickens fed polished white rice, whose discarded husks reversed the nerve signs of beriberi. Each vitamin was named by taking something away and watching what failed.
A mineral is a different kind of thing from everything else on the list. A vitamin is a molecule, built by something living. A mineral is an element — a single entry on the periodic table. Nothing living can make one, and nothing can destroy one.
Every mineral atom in you was pulled out of rock. Weathering releases it into soil, roots take it up in solution, and an animal eats the plant or you do. So the mineral content of a plant food depends on the ground it grew in, in a way the vitamin content does not.
Calcium
About 1.2 kilograms in an adult, 99% in bone and teeth. The other 1% runs nerve signalling and muscle contraction, and the body withdraws from the skeleton to hold it steady.
Magnesium
Around 25 grams, cofactor in several hundred enzyme reactions. Most ATP is bound to magnesium.
Potassium and sodium
The pair holding the electrical gradient across every cell membrane. A nerve impulse is that gradient collapsing and being rebuilt.
| Trace mineral | What it is needed for |
|---|---|
| Iron | The centre of haemoglobin, which is how oxygen moves |
| Zinc | Cofactor for hundreds of enzymes, and the structural atom in proteins that read DNA |
| Copper | Iron handling, connective tissue cross-linking, energy |
| Iodine | Thyroid hormone and nothing else — T3 and T4 are named for their iodine atoms |
| Selenium | Enzymes that maintain the body’s own antioxidant defences |
| Manganese, chromium, molybdenum | Bone formation; carbohydrate handling; clearing sulphur compounds |
Absorption is the whole game, and the figure on a label is what went into the capsule rather than what crossed your gut wall. Around 25 to 35% of dietary calcium is absorbed. Non-haem iron runs from 2 to 20% depending on what it arrived with; haem iron from meat runs two to three times higher. Phytates and oxalates bind minerals in the gut: only about 5% of spinach’s calcium is available, against 50% or more from broccoli.
A mineral on a label is never the bare element — elemental magnesium is a soft metal that catches fire in water. Magnesium oxide is around 60% magnesium by weight and poorly absorbed: what matters is not how much element sits in the compound but how much crosses the gut wall. A chelate — from the Greek for claw — holds the mineral in the grip of an amino acid, which keeps it soluble through the gut’s changes in acidity. Minerals of similar size and charge also share transporters, and sharing means competing: calcium and non-haem iron in one meal reduce each other’s uptake, and zinc and copper use the same route, so sustained high zinc with no copper lowers copper status over months. With minerals, the form on the label is the product — and every mineral in the nutrient library carries its own story.
Only two fatty acids are essential out of the dozens a body uses, and the reason is a single missing pair of enzymes. Plants can place a double bond beyond the ninth carbon of a fatty acid chain. Human cells cannot. Everything about omega-3 and omega-6 follows from that one gap.
The omega number is a counting convention: start at the methyl end of the chain and count to the first double bond. At carbon three it is an omega-3, at carbon six an omega-6. The two essential ones are linoleic acid and alpha-linolenic acid, both eighteen carbons long.
ALA — alpha-linolenic acid
The essential omega-3, from flax, chia and walnuts — the parent of the family. Its page covers sources and stability.
EPA — eicosapentaenoic acid
Twenty carbons, five double bonds. A starting material rather than a building block: the substrate for families of signalling molecules.
DHA — docosahexaenoic acid
Twenty-two carbons, six double bonds. Structural, concentrated in the brain’s grey matter and in the retina.
GLA — gamma-linolenic acid
The omega-6 downstream of linoleic acid, already formed in borage and evening primrose oil. Its page sets out where it sits.
The conversion problem is the practical heart of this. The body converts ALA to EPA and then to DHA as required — badly. Measured conversion of ALA to EPA is commonly 5 to 10%, and through to DHA usually under 1% in men. The bottleneck is an enzyme called delta-6 desaturase, and linoleic acid competes for it, so a diet heavy in omega-6 makes an already-poor conversion poorer.
The ratio question deserves an honest answer. The competition between the two families is real and measurable; the claim that human diets once ran near 1:1 rests on reconstructions with wide uncertainty. The lever worth pulling is raising EPA and DHA directly.
Diagram to come
A flow showing why fatty acid intake does not arrive where people assume. Two parallel chains left to right. Top, omega-3: ALA into EPA into DHA, the connecting arrows drawn proportionally narrow — ALA to EPA around a tenth the width of the chain, EPA to DHA narrower still. Bottom, omega-6: LA into GLA and onward, same shape. Both first conversions must pass through one shared gate labelled with the enzyme, so the competition reads as a visible bottleneck rather than a stated fact. A second route enters EPA and DHA directly from the side, bypassing the gate, labelled as the dietary route.
Every cell you have is bounded by a double layer of phospholipid — two sheets of molecules whose fatty acid tails face inward. Those tails are not a metaphor. They are the fatty acids you ate, built into the structure of the boundary. Shape decides behaviour: a saturated chain is straight and packs tightly into a stiffer membrane, while every double bond puts a kink in the chain, and kinked chains cannot pack. DHA has six double bonds in twenty-two carbons, one of the most flexible chains in biology — and membranes are crowded with receptors, ion channels and transporters, each of which changes shape to do its job, which it can only do if the fat around it permits the movement. Composition shifts over weeks and months, because it changes only as the membrane turns over.
Nothing in this section is essential. No requirement has been set for any of it and no deficiency state has ever been described. It is still the category that connects this course to the other half of the curriculum.
Phytonutrients are the compounds a plant makes for its own purposes — deterring what eats it, colouring what pollinates it, shielding it from sunlight. Nothing in a human body is built out of them. They arrive, interact with signalling already running, and leave, which puts them in the same bracket as an essential oil.
Polyphenols
Over eight thousand structures described — tea, berries, olive oil, almost every culinary herb. Quercetin is among the most studied.
Carotenoids
The red, orange and yellow pigments. A few convert into vitamin A; lutein concentrates in the macula instead.
Glucosinolates
Sulphur compounds particular to the brassicas, stored apart from the enzyme that activates them.
Terpenes
The largest class there is, and most of what is in a bottle of essential oil.
This category attracts more overstatement than any other. Most striking findings about individual phytonutrients come from laboratory work — isolated compounds applied to cells in a dish, at concentrations far above anything a meal produces in blood. That is not the same as what happens in a person, and a result in a dish must never be read as a result in a body. Better supported is the duller finding: diets rich in these compounds track with better long-term health.
Photograph to come
A close, honest still life of raw plant material sorted by pigment class rather than by meal: deep purple berries and red cabbage together, orange peppers and carrots together, dark leafy brassicas together, a citrus half showing the oil glands in the peel. Daylight, a worn wooden surface, nothing styled as a product shot. The citrus is the load-bearing item — its peel is the visual bridge to the oils half of the curriculum and must be in frame.
And here is the bridge. Terpenes are the class the science course is built around, and a limonene molecule from zest grated into a salad is identical to one from a bottle of lemon oil.
Water and fibre are missing from most nutrition charts for opposite reasons. Water is so obvious it stops being thought of as a nutrient; fibre is not absorbed, so it looks as though it cannot be doing anything.
Water meets the definition exactly: the body cannot produce enough, so it must be supplied. Oxidising fuel yields around 250 to 350 millilitres a day, against losses of two to three litres that continue whether or not anything is drunk. It is around 60% of adult body weight.
Fibre is carbohydrate the human small intestine has no enzyme for. It passes through undigested, and that is the point of it. The useful split is between two behaviours.
Soluble and fermentable
Pectin in apples, beta-glucan in oats, inulin in chicory. It dissolves into a gel, slowing stomach emptying and the rate at which glucose from the same meal reaches the blood.
Insoluble and bulking
Cellulose, hemicellulose and lignin — wheat bran, vegetable skins, nuts. It holds water and shortens transit time.
What happens to the fermentable fraction is the part worth carrying away. Bacteria in the large intestine ferment it into short-chain fatty acids, and butyrate is the primary fuel of the cells lining the colon — those cells take most of their energy from a molecule bacteria made out of fibre a few millimetres away. That is what prebiotic fibre means on a label. Recommendations sit around 25 to 30 grams a day; typical intake is about half that.
The other half is the numbers, and the numbers on a bottle are not measuring what most people assume.
EAR — Estimated Average Requirement
The intake meeting the requirement of half a group; the figure the others are built from.
RDA — Recommended Dietary Allowance
The EAR plus two standard deviations, covering 97 to 98% of healthy people in that group.
AI — Adequate Intake
Used where the evidence is too thin for an EAR.
UL — Tolerable Upper Intake Level
The highest daily intake judged unlikely to cause harm in almost anyone. Not a target but a ceiling, and what matters when several products carry the same nutrient.
DV and %DV
The label figure: one reference number per nutrient for everyone above four years old.
What those two figures are not
An RDA is a population figure built so that nearly everyone is covered, not a personal figure built to make anyone optimal. There is no agreed method for calculating optimal, which is why no authority publishes one. And a %DV is measured against one reference number rather than against you.
Vitamin D appears in both micrograms and international units, where 1 microgram equals 40 IU — so 1,000 IU and 25 micrograms are the same amount, and a panel quoting one while a lesson quotes the other looks like a disagreement when it is not. Vitamin A is given in retinol activity equivalents, because beta-carotene from a plant converts to retinol at roughly twelve to one by weight, so the same milligram figure means different things depending on the source. Vitamin E has its own version of the problem: the natural and synthetic forms are not equivalent unit for unit. Reading a supplement label takes a real panel apart line by line.
The reference figures themselves differ by country: a Daily Value in one market is a Nutrient Reference Value in another. The product range differs the same way — which supplements are available, and in what formulation, is not the same everywhere.
What no figure on any panel can know is the person holding the bottle. A supplement supplements a diet and does not replace food. Where a real question exists about your own status, that is the territory of testing and of professional medical care, which nothing here replaces.
These statements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure or prevent any disease. A dietary supplement does not replace a varied diet, and nothing here replaces professional medical care. If you are pregnant, nursing, under medical care or taking medication, speak to your healthcare practitioner before using any supplement. Product availability and label reference figures differ from market to market.
Everything here sits at the level of the category. The next level down is the individual nutrient — what it does, which systems it serves, and how well it absorbs.
Lesson 2 of 12 · Nutrition