Nutrition basicsAmino acidsProtein powdersBCAA & EAA
Proteins are built from 20 amino acids. Nine of them are essential — your body cannot make them, so they must come from food. Others are non-essential (your body makes them) or conditionally essential (essential only during illness, stress or rapid growth). What matters most for health is getting enough total protein of good quality; individual amino acids matter clinically in specific situations, covered below.
Read first — about the doses on this page. The requirements shown are population reference values; the therapeutic doses describe what is used in research and clinical practice. They are information, not a prescription. Single amino acids taken in gram doses are a form of supplement and can interact with medication and medical conditions. Always involve a doctor or pharmacist before therapeutic use, in pregnancy or breastfeeding, for a child, in kidney or liver disease, or alongside other medicines.
How the requirements are given. Adult amino-acid needs are set per kilogram of body weight (WHO/FAO/UNU 2007).1 To get your daily target, multiply by your weight — e.g. leucine 39 mg/kg × 70 kg ≈ 2.7 g/day. A varied diet that meets the overall protein target (see the protein-powder section) easily supplies all nine.
Essential — the branched-chain trio (BCAA)
Leucine, isoleucine and valine have a branched side-chain and are metabolised largely in muscle. Leucine is the strongest single trigger of muscle protein synthesis — but they work best as part of complete protein, not alone (see the BCAA verdict below).
Leucine
What it does: switches on the mTOR pathway that builds muscle protein; a per-meal "leucine threshold" of roughly 2–3 g maximises the muscle-building response to a meal.
Where you find it: whey and dairy (richest), eggs, meat, fish, soy; lower in most other plant proteins.
Isoleucine
What it does: energy metabolism in muscle, glucose uptake and haemoglobin formation. Where: meat, fish, eggs, dairy, soy, legumes, seeds.
Valine
What it does: muscle energy metabolism, tissue repair and nitrogen balance. Where: meat, dairy, eggs, soy, legumes, whole grains, mushrooms.
Essential — the other six
Lysine
What it does: builds collagen, helps make carnitine (for fat burning) and supports calcium absorption. It is the limiting amino acid in wheat, rice and maize — the one most likely to run short on a cereal-heavy, low-legume diet.
Where you find it: meat, fish, eggs, dairy, and among plants especially legumes (beans, lentils, soy).
Methionine (with cysteine = "sulfur amino acids")
What it does: the start signal for building every protein; donates methyl groups (as SAMe) for DNA and neurotransmitter reactions; converts to cysteine. Where: eggs, fish, meat, Brazil nuts, sesame and other seeds; lower in legumes.
Phenylalanine
What it does: converts to tyrosine, and from there to dopamine, noradrenaline and thyroid hormone. Where: meat, fish, eggs, dairy, soy, nuts and seeds; also in the sweetener aspartame.
Threonine
What it does: builds collagen and elastin, and the mucin that protects the gut lining; supports immune antibody production. Where: meat, fish, eggs, dairy, lentils, nuts and seeds.
Tryptophan
What it does: the precursor of serotonin and melatonin (mood and sleep) and a source of niacin (vitamin B3). Where: turkey, chicken, milk, cheese, eggs, oats, soy, nuts and seeds.
Histidine
What it does: makes histamine (immune and stomach-acid signalling), helps form haemoglobin, and combines with beta-alanine to make carnosine in muscle. Where: meat, fish, eggs, dairy, whole grains, beans.
Conditionally essential
Your body normally makes these, but during illness, injury, rapid growth or intense stress demand can outstrip supply — so they become "essential" in those situations. Several are also popular supplements.
Arginine
What it does: the raw material for nitric oxide, which widens blood vessels; also involved in wound healing and immune function. Where: nuts, seeds, meat, fish, soy, whole grains.
Cysteine (and NAC)
What it does: the rate-limiting building block of glutathione, the body's master antioxidant; also builds hair and nail keratin. Where: eggs, meat, dairy, garlic, onions, Brazil nuts, oats.
Glutamine
What it does: the most abundant amino acid in blood; a primary fuel for gut-lining and immune cells. Where: meat, fish, eggs, dairy, cabbage, beans; the body also makes large amounts.
Glycine
What it does: the simplest amino acid — a third of collagen, a building block of glutathione and creatine, and a calming neurotransmitter. Where: collagen-rich foods (skin, bone broth, gelatine), meat, fish, legumes.
Tyrosine
What it does: made from phenylalanine; the precursor of dopamine, noradrenaline and adrenaline and of thyroid hormone. Where: cheese, soy, meat, fish, eggs, nuts, seeds.
Proline & serine
What they do: Proline is a major structural component of collagen (skin, joints, blood vessels). Serine builds phospholipids and neurotransmitters and feeds one-carbon metabolism. Where: both are plentiful in ordinary protein foods, and the body makes them.
Non-essential amino acids
Alanine, glutamate, aspartate & asparagine
These are made in ample amounts from other nutrients, so there is no dietary requirement and no deficiency in healthy people.
Alanine: shuttles nitrogen and helps the liver make glucose during fasting. Note: the supplement beta-alanine is a different molecule — not used to build protein — that raises muscle carnosine and has good evidence for high-intensity exercise performance at ~3–6 g/day (harmless tingling is common).6
Glutamate: a major excitatory neurotransmitter and the savoury "umami" taste — the same compound as in MSG; dietary glutamate is handled routinely by the gut.
Aspartate & asparagine: feed energy metabolism and the urea cycle; abundant in ordinary food and made internally.
Amino-acid-related compounds
These three are not used to build protein — they are amino acids (or amino-acid derivatives) that act in their own right, and all three are common supplements, so they belong here.
Taurine
What it does: a sulfur-containing amino acid abundant in the heart, muscle, retina and brain; helps form bile salts, regulates fluid and calcium in cells, and acts as an antioxidant. The body makes some (from cysteine), so it is conditionally essential — genuinely essential for infants, which is why it is added to infant formula.
Where you find it: meat, fish and shellfish, and dairy; it is almost absent from plant foods, so vegans have lower levels (the body adapts by conserving it).
L-Carnitine
What it does: the shuttle that carries fatty acids into the mitochondria to be burned for energy — so it is central to how muscle and heart use fat. The body makes enough from lysine and methionine (plus vitamin C), so it is not essential in health.
Where you find it: red meat is by far the richest source; smaller amounts in fish, poultry and dairy; little in plants.
GABA (gamma-aminobutyric acid)
What it does: the brain's main calming (inhibitory) neurotransmitter, made from glutamate. It dials down nerve excitability — the same system targeted by anti-anxiety drugs.
Where you find it: made by the body; small dietary amounts in fermented foods, sprouted grains and some teas.
L-Theanine
What it does: an amino acid found almost only in tea (and a few mushrooms). It promotes calm alertness — raising relaxing alpha brain waves and nudging GABA, dopamine and serotonin — and famously smooths caffeine's edge, giving focus without jitters or drowsiness.
Where you find it: green and black tea (a few tens of mg per cup); supplements provide standardised doses.
Protein powders
Whey, casein, soy, pea, rice, oat, hemp and egg-white/collagen — compared honestly, with quality scores and who each one suits — now live on our Foods page. See the full protein-powders comparison →
BCAA (branched-chain amino acids)
What it is: just leucine, isoleucine and valine. The honest verdict: giving only three of the nine essential amino acids can't sustain protein synthesis as well as whole protein or a complete EAA blend, so BCAAs add little if your protein intake is already adequate.
EAA (essential amino acids)
What it is: a blend of all nine essential amino acids. Because it is complete, a small EAA dose can stimulate muscle protein synthesis effectively — the property BCAAs lack.
The honest bottom line: hit your total protein target from varied whole foods and you get every amino acid automatically. A whey, soy or pea/rice blend powder is a convenient top-up. Single amino acids (glycine, NAC, tyrosine, citrulline) have real but specific uses; BCAAs are mostly unnecessary and EAAs beat them when a supplement is genuinely warranted.
References
Amino-acid requirements are general adult reference values (per kg body weight); exact needs vary by age, sex and life stage. Therapeutic doses describe research/clinical use, not prescriptions.
- WHO/FAO/UNU. Protein and amino acid requirements in human nutrition. WHO Technical Report Series 935, 2007 — indispensable (essential) amino-acid requirements for adults. who.int
- Jäger R, et al. International Society of Sports Nutrition Position Stand: protein and exercise. J Int Soc Sports Nutr. 2017;14:20 (1.4–2.0 g/kg/day; per-meal dose & leucine). jissn.biomedcentral.com
- Trexler ET, et al. ISSN position stand: Beta-Alanine. J Int Soc Sports Nutr. 2015;12:30. jissn.biomedcentral.com
- EFSA Panel (ANS). Scientific Opinion on the use of taurine and D-glucurono-γ-lactone as constituents of energy drinks. EFSA Journal 2009;7(4):935 (taurine intakes up to ~6 g/day of no safety concern). efsa.onlinelibrary.wiley.com
- Singh P, et al. Taurine deficiency as a driver of aging. Science 2023;380(6649):eabn9257 (animal study). science.org
- US NIH Office of Dietary Supplements. Carnitine — Health Professional Fact Sheet (function, sources, deficiency, therapeutic evidence). ods.od.nih.gov
- Koeth RA, et al. Intestinal microbiota metabolism of L-carnitine, a nutrient in red meat, promotes atherosclerosis (TMAO). Nature Medicine 2013;19:576–585. nature.com
- Boonstra E, et al. Neurotransmitters as food supplements: the effects of GABA on brain and behavior. Frontiers in Psychology 2015;6:1520 (blood–brain-barrier & evidence discussion). frontiersin.org
- Hidese S, et al. Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial. Nutrients 2019;11(10):2362. mdpi.com
This article summarizes nutrition science from official health authorities and peer-reviewed sources for education. It is not a substitute for individual medical advice, and the doses given are not prescriptions — always consult a professional before therapeutic supplement use, in pregnancy, or alongside medication.