Clear evidence. Transparent sources. Practical guidance. Our evidence policyContact
Food Health Lab
Home › Nutrition › Protein & amino acids

Protein & Amino Acids — Requirements, Deficiency & Protein Powders

The building blocks of every protein in your body. This guide covers each amino acid — what it does, where you get it, how much you need and how it is used therapeutically — then a practical, honest look at protein powders, BCAA and EAA.

Reviewed by Bodil Isaksson, Licensed Biomedical Scientist (Sweden) Last reviewed July 2026 Reference guide

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

Requirement ≈ 39 mg/kg/dayMain MPS trigger

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.

DeficiencyOnly with overall protein malnutrition — loss of muscle and impaired repair.
Therapeutic useLeucine-enriched essential-amino-acid mixtures are studied for sarcopenia (age-related muscle loss) and clinical muscle wasting.3
Upper limitNo official UL; very high isolated leucine can lower B-vitamin status and disturb the other BCAA balance. Whole protein is the safer route.

Isoleucine

Requirement ≈ 20 mg/kg/day

What it does: energy metabolism in muscle, glucose uptake and haemoglobin formation. Where: meat, fish, eggs, dairy, soy, legumes, seeds.

DeficiencyPart of general protein deficiency — muscle wasting, fatigue.
Therapeutic useNo established single-amino-acid role beyond being part of dietary/EAA protein.
Upper limitNo official UL; take as part of balanced protein rather than in isolation.

Valine

Requirement ≈ 26 mg/kg/day

What it does: muscle energy metabolism, tissue repair and nitrogen balance. Where: meat, dairy, eggs, soy, legumes, whole grains, mushrooms.

DeficiencyPart of general protein deficiency.
Therapeutic useNo established isolated role; contributes as part of BCAA/EAA and dietary protein.
Upper limitNo official UL.

Essential — the other six

Lysine

Requirement ≈ 30 mg/kg/dayLimiting in cereals

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).

DeficiencyFatigue, poor growth, impaired immunity and slow wound healing; a real risk on monotonous grain-based diets with few legumes.
Therapeutic useOften tried for recurrent cold sores (herpes labialis) at ~1 g/day — the evidence is mixed and weak. Adding legumes to a grain diet is the more important use.
Upper limitNo official UL; gram doses can cause stomach upset. Caution in kidney disease.

Methionine (with cysteine = "sulfur amino acids")

Requirement ≈ 15 mg/kg/day (Met + Cys)

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.

DeficiencyRare on a mixed diet; methionine is the limiting amino acid in legumes, so very low-variety vegan diets should combine legumes with grains/seeds.
Therapeutic useMedical use in some metabolic and liver conditions; SAMe (a methionine derivative) is studied for depression and joint pain — specialist territory.
Upper limitNo official UL; high isolated intakes raise homocysteine and strain the liver. Balance with folate/B12.

Phenylalanine

Requirement ≈ 25 mg/kg/day (Phe + Tyr)Restricted in PKU

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.

DeficiencyRare with adequate protein.
Therapeutic useNo routine supplement role. The important clinical point is the opposite — restriction.
Upper limitNo general UL, but people with the genetic condition PKU (phenylketonuria) cannot break it down and must strictly limit phenylalanine, including aspartame — which is why diet drinks carry a PKU warning.

Threonine

Requirement ≈ 15 mg/kg/day

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.

DeficiencyUncommon; can impair gut and immune function in severe protein malnutrition.
Therapeutic useNo established single-amino-acid role in healthy people.
Upper limitNo official UL.

Tryptophan

Requirement ≈ 4 mg/kg/daySerotonin precursor

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.

DeficiencyContributes to low mood and, with low niacin, can worsen pellagra.
Therapeutic useStudied for sleep and mood at ~1 g (see the Sleep guide). Caution: can cause serotonin syndrome with antidepressants (SSRIs/MAOIs).
Upper limitNo official UL. A 1989 outbreak of eosinophilia–myalgia syndrome was traced to a contaminated supplement batch, not tryptophan itself; use pharmaceutical-grade products only.

Histidine

Requirement ≈ 10 mg/kg/day

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.

DeficiencyAnaemia has been linked to low histidine; needs are relatively higher in infancy and in kidney dialysis patients.
Therapeutic useInvestigated in anaemia of kidney disease and in some inflammatory conditions; not a routine supplement.
Upper limitNo official UL.

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

Studied: 3–6 g/day (or citrulline)

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.

DeficiencyConditionally essential after major trauma, burns or surgery.
Therapeutic useStudied for blood-flow and exercise; much of the oral dose is broken down in the gut, so L-citrulline (≈3–6 g) raises arginine levels more reliably.
Upper limitNo official UL; can lower blood pressure and may reactivate herpes (it opposes lysine). Caution after heart attack and with blood-pressure medicine.

Cysteine (and NAC)

NAC studied: 600–1200 mg/dayGlutathione precursor

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.

DeficiencyUncommon; can fall in severe illness, lowering glutathione.
Therapeutic useIts supplement form N-acetylcysteine (NAC) is a genuine medicine — the hospital antidote for paracetamol (acetaminophen) overdose and a mucus-thinner in lung disease; also studied in psychiatry.
Upper limitNo official UL; NAC can cause nausea and, rarely, allergic reactions. Use medically where it is a treatment.

Glutamine

Clinical use: 0.2–0.5 g/kg/day

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.

DeficiencyConditionally essential in critical illness, major burns and severe gut disease, when demand outstrips production.
Therapeutic useUsed in clinical nutrition for critically ill and post-surgical patients. Popular sports/"gut-healing" supplements have weak evidence in healthy, well-fed people.
Upper limitNo official UL; generally well tolerated. Caution in liver disease (raises ammonia).

Glycine

Studied: 3 g/day for sleep

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.

DeficiencyNot a classic dietary deficiency, but synthesis may not fully meet needs for collagen turnover.
Therapeutic use3 g before bed has modest evidence for better sleep quality (see the Sleep guide); also studied for metabolic health.
Upper limitNo official UL; well tolerated, occasional mild GI upset.

Tyrosine

Studied: 100–150 mg/kg (acute stress)

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.

DeficiencyBecomes essential in PKU, where phenylalanine can't be converted, so tyrosine is supplemented.
Therapeutic useBest evidence is for maintaining mental performance during acute stress (sleep loss, cold, heavy cognitive load); little benefit when rested.
Upper limitNo official UL; caution with thyroid medication, MAOI antidepressants and melanoma.

Proline & serine

No supplement requirement

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.

DeficiencyNot a recognised dietary deficiency in healthy people.
Therapeutic useNo routine supplement role; proline is supplied naturally by collagen/gelatine and vitamin C is needed to use it for collagen.
Upper limitNo official UL.

Non-essential amino acids

Alanine, glutamate, aspartate & asparagine

Made by the body — no dietary requirement

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

Studied: 1–6 g/dayVery low in plants

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).

DeficiencyRare in adults; matters most in infancy, dialysis and some heart conditions.
Therapeutic useThe active ingredient in most energy drinks (~1 g); some trials suggest benefit in heart failure and for exercise. A 2023 study showed taurine declines with age and reversing it extended lifespan in animals9 — intriguing, but not yet proven to do the same in humans.
Upper limitNo official UL; EFSA judged intakes up to ~6 g/day safe.8 Generally well tolerated.

L-Carnitine

Studied: 1–3 g/dayMade from lysine + methionine

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.

DeficiencyPrimary (genetic) carnitine deficiency, or secondary to dialysis or certain drugs (e.g. valproate) — causes muscle weakness and low blood sugar.
Therapeutic useProven for genuine deficiency. Studied — with mixed results — for angina/heart failure, male fertility and fatigue; acetyl-L-carnitine is the brain-targeted form. Weight-loss/fat-burner claims are weak.10
Upper limitNo official UL; ~3 g/day can cause nausea and a fishy body odour. Honest caveat: gut bacteria turn carnitine into TMAO, a compound linked in research to cardiovascular risk — a reason not to megadose long-term.11

GABA (gamma-aminobutyric acid)

Studied: 100–300 mgAbsorption to brain uncertain

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.

DeficiencyNot a dietary deficiency — the brain makes its own from glutamate (with vitamin B6).
Therapeutic useSold for stress, relaxation and sleep (~100–300 mg). Honest evidence note: it is unclear how much oral GABA reaches the brain, since it doesn't cross the blood–brain barrier well; any effect may work via the gut nervous system or expectation. Evidence is preliminary and mixed.12
Upper limitNo official UL; generally well tolerated at supplement doses. Caution combining with sedatives or blood-pressure medication.

L-Theanine

Studied: 100–400 mgThe "calm" in tea

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.

DeficiencyNot a nutrient — no deficiency; it is a bioactive compound rather than an essential amino acid.
Therapeutic useReasonable evidence at 100–400 mg for stress and relaxation and for calmer focus when paired with caffeine; also studied for sleep quality (it relaxes rather than sedates — see the Sleep guide).13
Upper limitNo official UL; very well tolerated. Mild caution: may add to the blood-pressure-lowering effect of some medication.

Protein powders & supplements

You don't need a powder — whole foods work — but a scoop is a convenient way to hit a protein target, especially for older adults, athletes, vegans or anyone with a small appetite.

How much protein? The basic RDA is 0.8 g/kg/day to prevent deficiency. For building or preserving muscle — during training, weight loss or ageing — evidence supports 1.2–2.0 g/kg/day, split across meals with ~20–40 g (and ~2–3 g leucine) per serving.23

What "quality" means. A complete protein supplies all nine essential amino acids in good amounts. Quality is scored by PDCAAS/DIAAS.4 Whey, casein, egg and soy score highest; single plant proteins are usually "incomplete" (short in one amino acid) but combining them fixes this.

Whey protein

~20–30 g/servingFast · complete · high leucine

What it is: a fast-digesting complete milk protein, the richest common source of leucine — ideal around training. Concentrate (~70–80% protein, some lactose) is the everyday, lower-cost grade; isolate (~90%, very low lactose) suits lactose-sensitive people; hydrolysate is pre-digested and fastest.

Note: contains milk — not for dairy allergy; isolate is usually fine for mild lactose intolerance.

Casein

~20–40 g/servingSlow · complete

What it is: the other milk protein — slow-digesting (micellar casein forms a gel in the stomach), releasing amino acids over hours. Popular before bed or as a meal replacement to keep amino acids topped up. Also a complete, dairy-based protein.

Soy protein

~20–30 g/servingComplete plant protein

What it is: the best-scoring plant protein — complete, with a full essential-amino-acid profile close to whey for muscle building. It naturally contains isoflavones (phytoestrogens); as covered on our Phytochemicals page, normal soy intake does not lower testosterone or feminise men. A solid choice for vegans.

Pea protein

~20–30 g/servingHypoallergenic · low methionine

What it is: a well-tolerated plant protein, high in BCAA, lysine and arginine but a little low in methionine. Dairy- and soy-free. Emerging trials show it can build muscle comparably to whey when total protein is matched. Often blended with rice to complete the profile.

Rice protein

~20–30 g/servingLow lysine — combine

What it is: hypoallergenic and easy to digest, but low in lysine so incomplete on its own. Pea + rice blends are the classic vegan fix — together they cover each other's gaps and rival whey.

Egg-white & collagen — two special cases

Egg = complete · Collagen = incomplete

Egg-white protein: a complete, lactose-free, high-quality protein — a good option for dairy-avoiders who eat eggs.

Collagen: popular for skin and joints, but it is an incomplete protein — it lacks tryptophan and is low in essential amino acids, so it is not a good muscle-building protein. Use it for its specific collagen-peptide purpose, not as your main protein.

BCAA (branched-chain amino acids)

Typical: 5–10 gOverhyped for most people

What it is: just leucine, isoleucine and valine. The honest verdict: to actually build muscle you need all nine essential amino acids; giving only three can't sustain protein synthesis, so BCAAs are inferior to whole protein or EAA and add little if your protein intake is already adequate.5

Where they helpA genuine medical use is hepatic encephalopathy in liver disease, where BCAAs improve symptoms.7 A minor niche is training fasted when no other protein is available.
Bottom lineFor most people, spend the money on whole protein or EAA instead.

EAA (essential amino acids)

Typical: 6–15 gBetter than BCAA

What it is: a blend of all nine essential amino acids. Because it is complete, a small EAA dose (~6–15 g, with enough leucine) can stimulate muscle protein synthesis effectively — the property BCAAs lack.5

Who it suits: useful when a full protein feed isn't practical (e.g. some older or clinical settings, or intra-workout). For most healthy people a normal protein-rich meal or a whey/soy shake does the same job.

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.

← Macronutrients (protein overview) Vitamins →
✓
Bodil Isaksson, Licensed Biomedical Scientist (Sweden)

At Food Health Lab we explain what the science says in plain language, and we cite our sources so you can check for yourself.

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.

  1. 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
  2. EFSA Panel (NDA). Scientific Opinion on Dietary Reference Values for protein. EFSA Journal 2012;10(2):2557 (PRI 0.83 g/kg/day). efsa.onlinelibrary.wiley.com
  3. 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
  4. FAO. Dietary protein quality evaluation in human nutrition (DIAAS). FAO Food and Nutrition Paper 92, 2013. fao.org
  5. Wolfe RR. Branched-chain amino acids and muscle protein synthesis in humans: myth or reality? J Int Soc Sports Nutr. 2017;14:30. jissn.biomedcentral.com
  6. Trexler ET, et al. ISSN position stand: Beta-Alanine. J Int Soc Sports Nutr. 2015;12:30. jissn.biomedcentral.com
  7. Gluud LL, et al. Branched-chain amino acids for people with hepatic encephalopathy. Cochrane Database of Systematic Reviews 2017, CD001939. cochranelibrary.com
  8. 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
  9. Singh P, et al. Taurine deficiency as a driver of aging. Science 2023;380(6649):eabn9257 (animal study). science.org
  10. US NIH Office of Dietary Supplements. Carnitine — Health Professional Fact Sheet (function, sources, deficiency, therapeutic evidence). ods.od.nih.gov
  11. 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
  12. 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
  13. 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.

Read next

Nutrition
Macronutrients
Nutrition
Fatty acids