Nine of the twenty amino acids that build human protein cannot be made by your body, so they have to come from food: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine. Meat, fish, eggs, dairy and soya supply all nine. So does a varied plant diet across a day.
Most pages on this subject list the nine, name a food for each, then point you at a tub of powder. The list is correct and the powder is usually pointless.
What almost nothing written for a British reader covers is the part that actually changes with age: how much protein you need per meal, why that number rises after 65, and which single amino acid decides whether a meal registers with your muscle at all. That is where this article spends its time.
What are essential amino acids, and how many are there?
Twenty amino acids build human proteins. Your liver can manufacture eleven of them from other molecules. The other nine it cannot, or cannot make fast enough to keep up with demand, so they must arrive in your diet. Those nine are the ones called essential.
The word causes more confusion than any other in nutrition. It does not mean these nine matter more than the rest. Alanine is just as necessary for building a protein. It means only that your body has no route to make them, so the diet is the sole supply. The confusion runs the other way too: L-theanine is an amino acid your body never builds into a protein at all, which is why it behaves nothing like the nine.
A third group sits in between, described as conditionally indispensable: arginine, cysteine, glutamine, glycine, proline and tyrosine. Your body makes them, but during severe illness, injury or in premature infants, production falls short of need and they have to be supplied as well. Two of them, glycine and proline, are also the amino acids collagen is unusually rich in, which is why collagen peptides get discussed as though they were an amino acid supplement.
The nine, and what each one does
Two of them, tyrosine and cysteine, are made from an amino acid in this list, which is why methionine and phenylalanine requirements are often quoted as pairs.
| Amino acid | What it is used for | Rich sources |
|---|---|---|
| Histidine | Precursor to histamine, needed for immune response and nerve insulation | Meat, fish, wholegrains |
| Isoleucine | Branched-chain, used in muscle metabolism and haemoglobin production | Eggs, fish, lentils |
| Leucine | Branched-chain, the trigger for muscle protein synthesis | Whey, dairy, soya, beef |
| Lysine | Collagen cross-linking, calcium absorption, carnitine synthesis | Pulses, dairy, meat. Low in cereals |
| Methionine | Methyl donor, precursor to cysteine | Eggs, fish, brazil nuts. Low in pulses |
| Phenylalanine | Precursor to tyrosine, then to dopamine and adrenaline | Dairy, meat, soya |
| Threonine | Collagen and elastin, gut mucin production | Cottage cheese, poultry, pulses |
| Tryptophan | Precursor to serotonin, melatonin and niacin | Turkey, oats, seeds, dairy |
| Valine | Branched-chain, muscle metabolism and energy | Dairy, soya, peanuts |
Notice the two gaps in the last column. Cereals run low on lysine, pulses run low on methionine. That single fact produced decades of advice about combining rice and beans in the same meal, and it is the piece the research has since revised.
What a shortfall looks like
Frank deficiency is rare in the UK and looks nothing like the vague symptom lists sold alongside amino acid powders. A genuine protein shortfall shows up as muscle wasting, poor wound healing, thinning hair, oedema and repeated infections, and it appears in specific situations: severe illness, cancer cachexia, malabsorption, alcohol dependence, or an older person living alone who has stopped cooking.
The far more common British problem is not deficiency but drift. Appetite falls with age, meals get smaller, and protein quietly slides from adequate to marginal over years without producing a single symptom you could name. Muscle mass declines by roughly 1 per cent a year after 50, and the first sign is usually functional: a handrail used on stairs, a shopping bag that feels heavier than it did. That drift is what the gap between years lived and years lived in good health looks like from the inside, and in England that gap runs to roughly two decades.
If that describes you, the useful check is not a blood test. It is counting the protein in a normal day, meal by meal, against the numbers in the next section.
How much do you actually need?
The UK reference nutrient intake for protein is 0.75 g per kilogram of body weight per day. For a 70 kg adult that is about 53 g, which sounds like a lot until you cost it out: a chicken breast, a pot of Greek yoghurt and two eggs get you most of the way.
That figure is a floor, not a target. It was set as the amount that prevents deficiency in almost everyone, and it says nothing about the intake that builds or preserves muscle.
For that question, Morton and colleagues pooled 49 randomised trials covering 1 863 people doing resistance training. Protein supplementation increased strength and fat-free mass, and a breakpoint analysis found the gains stopped improving above a total intake of 1.62 g per kilogram per day. Above that, more protein added nothing measurable.
PROTEIN INTAKE, FROM DEFICIENCY FLOOR TO CEILING
nutrient intake
0.75
1.0 to 1.2
active, 1.2 plus
above 1.62
Between those two numbers sits almost everyone. If you are sedentary and well, 0.75 is adequate. If you train, or you are over 65, or you are recovering from something, the evidence points higher.
Why the answer changes after 65
Ageing muscle does not respond to protein the way young muscle does. The phenomenon has a name, anabolic resistance, and it is the reason a diet that maintained your muscle at 40 quietly stops maintaining it at 70.
Moore and colleagues measured it directly. They pooled dose-response data in healthy men, feeding varying amounts of high-quality protein and tracking myofibrillar protein synthesis. Resting rates were identical between the two age groups. What differed was the dose needed to reach a plateau.
PROTEIN PER MEAL NEEDED TO MAXIMISE MUSCLE PROTEIN SYNTHESIS
Two thirds more protein per meal, for the same effect. Part of the reason is splanchnic extraction: the gut and liver of an older adult take a larger share of ingested amino acids before they reach the circulation.
The PROT-AGE study group turned that biology into a recommendation. Healthy adults over 65 should aim for 1.0 to 1.2 g per kilogram per day, more if they exercise, and 1.2 to 1.5 g if they are managing acute or chronic illness. That is well above the UK reference intake, and it is the single most useful number in this article.
Distribution matters as much as the total. Three meals of 30 g beat one of 90 g, because each meal has to clear the threshold on its own to trigger a synthesis response. Most British eating patterns load protein into the evening and leave breakfast at almost none.
Leucine, and the threshold nobody mentions
Among the nine, one behaves differently. Leucine is not just a building block, it is a signal: it activates the pathway that tells a muscle cell to start assembling protein. Below a certain amount of leucine in a meal, the switch does not flip.
Katsanos and colleagues showed this cleanly. They gave 6.7 g of amino acids to younger and older adults, in two versions: one matching the leucine content of whey at 26 per cent, and one enriched to 41 per cent. In the young, both raised muscle protein synthesis. In the older group, the 26 per cent mixture did nothing measurable. Only the 41 per cent version worked.
Practically, that means an older adult needs roughly 2.5 to 3 g of leucine in a meal, which arrives with about 30 g of a good-quality protein: a large chicken breast, a tin of tuna and an egg, 200 g of Greek yoghurt with seeds, or a generous portion of tofu with lentils.
It also explains why a token amount of protein at breakfast achieves nothing. Two slices of toast carry perhaps 0.4 g of leucine. The meal registers as food, not as a signal.
Which foods contain all nine?
All of them, in the sense that every whole food protein contains all nine amino acids. What varies is the proportion relative to human requirements, and that is what the word complete is really describing.
Animal proteins, soya, quinoa and buckwheat match human requirements closely. Cereals fall short on lysine, pulses on methionine, which is where the old rice-and-beans advice came from.
Mariotti and Gardner reviewed that advice and found it overstated. Your body holds a free amino acid pool and recycles a large quantity of protein daily, so amino acids from lunch remain available to combine with those from dinner. Complementing within a single meal is not required. Eating varied plant protein across a day is.
The one group who should pay attention are people eating a narrow plant diet with a low total protein intake. A vegan diet built on cereals with few pulses can genuinely run short on lysine. Adding beans, lentils, tofu or peanuts fixes it without a supplement.
Do EAA supplements do anything?
For most people, no, and two studies explain why.
WHAT THE TUB IMPLIES
THE MARKETING LOGIC
- Free-form amino acids absorb faster than food protein.
- BCAAs alone are enough to build muscle.
- More amino acids means more muscle, at any intake.
WHAT THE STUDIES FOUND
- 18 g of EAA matched 40 g of complete amino acids in older adults.
- BCAAs alone cannot maximise synthesis: all nine are needed.
- Above 1.62 g/kg/day of total protein, extra adds nothing.
Volpi and colleagues compared 18 g of the nine on their own against 40 g of a balanced mixture including the non-essential ones, in healthy older volunteers. Muscle protein balance improved with no difference between the groups, which established that the nine do the work. That is a genuine finding, and it is the honest case for EAA products.
Wolfe then dismantled the narrower claim. Branched-chain amino acids on their own, leucine, isoleucine and valine, cannot maximally stimulate muscle protein synthesis, because building a protein requires all nine. A BCAA drink supplies the signal and withholds most of the bricks.
So where do EAA powders earn their place? Poor appetite in older age or during illness, when 30 g of protein at a sitting is genuinely difficult. Medically supervised low-protein diets, where prescribed amino acid mixtures replace dietary protein. And inherited metabolic conditions such as phenylketonuria, where specialist formulas are treatment rather than supplementation. Outside those situations, a food-first approach costs less and works as well, which is roughly the same conclusion the evidence reaches for most supplements taken for ageing tissue.
Safety, and who should ask first
Protein at the intakes discussed here is well tolerated in healthy adults, and the idea that a high-protein diet damages healthy kidneys has not held up in trials.
Existing kidney disease is a different matter. The PROT-AGE group flagged that people with severe chronic kidney disease, an estimated GFR below 30 and not on dialysis, need their protein intake managed by a clinician rather than raised on general advice. Anyone with phenylketonuria must avoid phenylalanine-containing products, which includes most EAA powders.
If you are over 65 and reading this because you have noticed strength slipping, protein alone will not fix it. Resistance training is what makes the amino acids useful, and the two work together or barely at all. Where stiff, painful joints are the barrier to training, that obstacle deserves its own attention, and the evidence for approaches aimed at joint comfort sits separately from anything on this page.
The short version, if you take one thing away: 30 g of protein at each of three meals, from food, plus something heavy to lift twice a week. The tub is optional.
Frequently asked questions
What are the 9 essential amino acids?
Histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine. Your body cannot synthesise them, so they must come from food. A further group, including arginine, cysteine and tyrosine, becomes indispensable during illness or in premature infants.
Which food has all 9 essential amino acids?
Every whole food protein contains all nine. Meat, fish, eggs, dairy, soya, quinoa and buckwheat match human requirements most closely. Cereals are relatively low in lysine and pulses in methionine, which is why a varied plant diet matters more than any single food.
Do I need to combine proteins in the same meal?
No. That advice came from the lysine and methionine gap between cereals and pulses, but your body maintains a free amino acid pool and recycles protein continuously, so amino acids from lunch stay available at dinner. Variety across the day is what counts.
How much protein do I need per day?
The UK reference nutrient intake is 0.75 g per kilogram of body weight, about 53 g for a 70 kg adult. That is a deficiency floor. Adults over 65 are advised 1.0 to 1.2 g per kilogram, and resistance training gains stop improving above 1.62 g per kilogram.
What supplement has all 9 essential amino acids?
EAA powders and tablets contain all nine, and whey, casein, egg and soya protein powders do too. In healthy older adults, 18 g of the nine matched 40 g of a full amino acid mixture, so the nine are what matters. Food supplies them at lower cost.
Are BCAAs as good as EAAs?
No. Branched-chain amino acids supply leucine, isoleucine and valine, which signal muscle to build, but building requires all nine. Wolfe set this out in 2017: BCAAs alone cannot maximally stimulate muscle protein synthesis, because the remaining six are missing.
Can too much protein damage your kidneys?
In healthy adults, higher protein intakes have not been shown to harm kidney function. Existing kidney disease is different: with an estimated GFR below 30 and not on dialysis, protein intake should be set by a clinician rather than raised on general advice.
Sources
- Bauer J., Biolo G., Cederholm T., et al. Evidence-based recommendations for dietary protein intake in older people: a position paper from the PROT-AGE Study Group. Journal of the American Medical Directors Association, 2013. DOI: 10.1016/j.jamda.2013.05.021
- Moore D.R., Churchward-Venne T.A., Witard O., et al. Protein ingestion to stimulate myofibrillar protein synthesis requires greater relative protein intakes in healthy older versus younger men. The Journals of Gerontology Series A, 2015. DOI: 10.1093/gerona/glu103
- Morton R.W., Murphy K.T., McKellar S.R., et al. A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults. British Journal of Sports Medicine, 2018. DOI: 10.1136/bjsports-2017-097608
- Katsanos C.S., Kobayashi H., Sheffield-Moore M., Aarsland A., Wolfe R.R. A high proportion of leucine is required for stimulation of the rate of muscle protein synthesis by essential amino acids in the elderly. American Journal of Physiology Endocrinology and Metabolism, 2006. DOI: 10.1152/ajpendo.00488.2005
- Volpi E., Kobayashi H., Sheffield-Moore M., Mittendorfer B., Wolfe R.R. Essential amino acids are primarily responsible for the amino acid stimulation of muscle protein anabolism in healthy elderly adults. The American Journal of Clinical Nutrition, 2003. DOI: 10.1093/ajcn/78.2.250
- Wolfe R.R. Branched-chain amino acids and muscle protein synthesis in humans: myth or reality? Journal of the International Society of Sports Nutrition, 2017. DOI: 10.1186/s12970-017-0184-9
- Mariotti F., Gardner C.D. Dietary protein and amino acids in vegetarian diets: a review. Nutrients, 2019. DOI: 10.3390/nu11112661
This article is general information, not medical advice. Speak to your GP or a registered dietitian before changing your protein intake if you have kidney disease, liver disease, an inherited metabolic condition, or are pregnant.
