Essential Amino Acids: The Nine, Their Roles and Food Sources
The nine essential amino acids, what each does, which foods supply them, what official sources say about needs, and what essential amino acid supplements have and have not been shown to do.
Content last updated . This page has not been medically reviewed.
Overview
Amino acids are the building blocks of protein. The body uses them to make proteins that help it break down food, grow and repair tissue, and they can also serve as a fuel. [1] Nine are called essential because the body cannot make them, so they must come from food: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine. [1]This page is the home for the nine as a group. Four have their own guides: BCAAs (leucine, isoleucine and valine), tryptophan, lysine and leucine and muscle building. Histidine, methionine, phenylalanine, threonine and valine share one combined guide. For protein as a whole, see protein foundations.
Essential, conditionally essential and other amino acids
MedlinePlus sorts amino acids into three groups. [1]| Group | What MedlinePlus says | Examples it lists |
|---|---|---|
| Essential | Cannot be made by the body, so they must come from food. [1] | Histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine |
| Nonessential | The body can produce them even if food does not supply them. [1] | Alanine, asparagine, aspartic acid, glutamic acid, serine (and others) |
| Conditionally essential | Usually not essential, except in times of illness and stress. [1] | Arginine, cysteine, glutamine, tyrosine, glycine, proline, serine |
MedlinePlus lists some amino acids (for example arginine, glycine and glutamine) in both the nonessential and conditionally essential lists, which shows how blurry the edges are. [1]
Some products sold as "amino acids" are not protein-building amino acids at all. Taurine, for example, is described as one of the few amino acids not incorporated into proteins. [2] See taurine, carnitine and glutamine for those.
What each essential amino acid does
- Histidine is required to make proteins, and it is the starting material for carnosine (found in muscle and parts of the brain) and, by a separate step, for histamine. [3]
- Leucine, isoleucine and valine are the branched-chain amino acids. They are found in protein-rich foods such as milk, meat and eggs, and people with maple syrup urine disease cannot break them down normally. [4]
- Phenylalanine is found in all proteins, and people with phenylketonuria (PKU) cannot process it normally. [5]
- Lysine and methionine are the building blocks the body uses to make carnitine. [6]
- Threonine and tryptophan are essential and must come from food. [1] Tryptophan is also the starting material for serotonin; see the tryptophan guide.
Food sources
Amino acids are found in animal sources such as meats, milk, fish and eggs, and in plant sources such as soy, beans, legumes, nut butters and some grains such as wheat germ and quinoa. [7] MedlinePlus says you do not need to eat animal products to get all the protein you need. [7]Plant and animal foods differ in pattern. A review of food composition found that cysteine, glycine, lysine, methionine, proline, threonine and tryptophan generally occur in low amounts in plant products but are enriched in animal products. [8] A 2025 review adds that diets high in whole-food plant protein may need more total protein and energy to make up for lower protein quality, and that for incomplete plant proteins, eating complementary proteins may help. [9]
MedlinePlus says you do not need to eat all the essential amino acids at every meal, but the balance over the whole day matters, and a diet based on a single plant item will not be adequate. [1] Per-food amino acid amounts were not read for this page, so none are quoted; see protein quality and complementary proteins.
Official intake figures
| Item | Figure | Population and form | Source and year |
|---|---|---|---|
| Total protein, RDA | 0.80 g per kg body weight per day (56 g/day for males, 46 g/day for females) | Adults 19 years and over, Dietary Reference Intakes as presented by Health Canada; this is total protein, not individual amino acids | Health Canada DRI macronutrient table [10] (page updated 2025; values from the 2005 DRIs [11]) |
| Total protein, EAR | 0.66 g per kg body weight per day | Same group | Health Canada [10] |
Health Canada also gives a scoring pattern in mg of each amino acid per gram of protein, for judging how well a food protein matches needs (people aged 1 year and over): histidine 18, leucine 55, lysine 51, tryptophan 7, valine 32. [10] This is a yardstick for food protein quality. It is not a daily target for any individual amino acid.
The per-kilogram requirement for each essential amino acid in adults could not be verified from a page of NIH ODS, EFSA, the NHS, MedlinePlus or Health Canada, so none is quoted. A 2025 systematic review found limited requirement studies across the life cycle, particularly in pregnancy, lactation, infancy, childhood and adolescence. [11] How requirements are set is explained on how protein requirements are set.
Do essential amino acid supplements help?
Essential amino acid (EAA) supplements are powders or capsules with some or all of the nine. Evidence labels: established nutritional role, promising but limited, mixed, insufficient evidence.| Question | What the source found | Label |
|---|---|---|
| Needed from food? | All nine must come from food. [1] | Established nutritional role |
| Older adults, BCAA-rich supplements | A meta-analysis of 35 randomized trials found small benefits for strength, muscle mass and physical performance, with high variation between studies. [12] | Promising but limited |
| Healthy people eating enough protein | A review of muscle supplements rated evidence for BCAAs as mixed or unclear. [13] | Mixed |
| Whether to buy a "complete EAA" product instead of food | Proper evidence not found in the sources read (searched: PubMed reviews on essential amino acid supplementation; none read that compared such products with ordinary protein). | Insufficient evidence |
Study amounts are not advice. Compare the options on EAA supplements and BCAAs vs EAAs vs complete protein.
Upper limits
A 2023 review notes that national health agencies have not set tolerable upper intake levels for amino acids because of a lack of well-conducted human dose-response trials. [14] Under an initiative of a nonprofit amino acid science council, researchers proposed first values from clinical studies of healthy adults, for example no-observed-adverse-effect levels of 6 g a day for lysine and 8 g a day for histidine. [14] These are research estimates in healthy adults, not official limits, and do not apply to people with kidney or liver disease or metabolic disorders.Related
Protein for older adults and plant-based dietsFrequently asked questions
What are the nine essential amino acids?
Histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine. [1]
Are glutamine, arginine and taurine essential amino acids?
MedlinePlus lists arginine and glutamine as conditionally essential, meaning they may be needed from outside in illness or stress. [1] Taurine is described as one of the few amino acids not incorporated into proteins. [2]
Do I need to eat all nine at every meal?
No. MedlinePlus says the balance over the whole day is what matters. [1]
Can I get all of them on a vegetarian or vegan diet?
MedlinePlus says you do not need animal products to get the protein you need, but a diet based on a single plant item will not be adequate. [7][1] Variety across the day is the point.
Is there an upper limit for amino acid supplements?
Not from national health agencies, according to a 2023 review; researchers have proposed first values for some, from studies run under the initiative of a nonprofit amino acid science council. [14]
More details: evidence, limits and cautions
The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.
Safety and who should ask first
- PKU, maple syrup urine disease and other inherited amino acid disorders: these conditions need medical diet management. In PKU, phenylalanine can build up to harmful levels, [5] and in maple syrup urine disease leucine, isoleucine and valine build up and are toxic to the brain and other organs. [4] Do not add amino acid products without the metabolic team.
- Kidney and liver disease, pregnancy, breastfeeding, children and older adults: the sources read did not give supplement-specific guidance, so ask a clinician or pharmacist first. See amino acid supplements in pregnancy, children and older adults and protein and kidney disease.
- Medicines: see medication interactions and amino acid supplements and medicines.
- Before surgery: tell your surgical team about every supplement (supplements before surgery). The sources read did not describe amino acid-specific surgical risks.
- Quality: labels and contents can differ from what is on the pack; see quality testing and certifications.
If a child may have swallowed a large amount of any supplement, call Poison Help at 1-800-222-1222 (US) or 911 if the child is unwell.
References
- MedlinePlus. Amino acids. National Library of Medicine, US. Review date 1/21/2025. Read 2026-10-22.
- Ripps H, Shen W. Review: taurine: a "very essential" amino acid. Mol Vis. 2012. Read 2026-10-22.
- Brosnan ME, Brosnan JT. Histidine metabolism and function. J Nutr. 2020. Read 2026-10-22.
- MedlinePlus Genetics. Maple syrup urine disease. National Library of Medicine, US. Read 2026-10-22.
- MedlinePlus Genetics. Phenylketonuria. National Library of Medicine, US. Read 2026-10-22.
- Almannai M et al. Carnitine inborn errors of metabolism. Molecules. 2019. Read 2026-10-22.
- MedlinePlus. Protein in diet. National Library of Medicine, US. Read 2026-10-22.
- Li P, He W, Wu G. Composition of amino acids in foodstuffs for humans and animals. Adv Exp Med Biol. 2021. Read 2026-10-22.
- Matthews JJ et al. Understanding dietary protein quality: digestible indispensable amino acid scores and beyond. J Nutr. 2025. Read 2026-10-22.
- Health Canada. Dietary reference intakes tables: Reference values for macronutrients. Government of Canada, page dated 2025-11-19. Read 2026-10-22 through a web-fetch tool that summarised the page; rows as reported by that tool.
- Burstad KM et al. Evaluation of dietary protein and amino acid requirements: a systematic review. Am J Clin Nutr. 2025. Read 2026-10-22.
- Bai GH et al. Effects of branched-chain amino acid-rich supplementation on EWGSOP2 criteria for sarcopenia in older adults: systematic review and meta-analysis. Eur J Nutr. 2022. Read 2026-10-22.
- Valenzuela PL et al. Supplements with purported effects on muscle mass and strength. Eur J Nutr. 2019. Read 2026-10-22.
- Elango R. Tolerable upper intake level for individual amino acids in humans: a narrative review of recent clinical studies. Adv Nutr. 2023. Read 2026-10-22.