In 30 seconds
- There are 9 essential amino acids: your body does not make them, so they have to come from food. Three of them are the BCAAs: leucine, isoleucine and valine.
- In animal protein, essential amino acids make up 37% of the protein on average; in plant protein, 26%. Whey protein reaches 43%.
- BCAAs account for around 25% of the amino acids in complete proteins, and leucine is the signal that switches on muscle protein synthesis.
- You do not need to combine proteins at every meal: what counts is the balance over the whole day.
Essential amino acids are the 9 that your body cannot make and that have to come from food. They are in any complete protein: meat, fish, eggs and dairy. You can also cover them with plant proteins, by combining sources over the day.
The building blocks of protein
9 are essential, and 3 of them are the BCAAs
What amino acids are
They are the building blocks of proteins, both those in your food and those in your muscles. Your body uses two main groups 1:
- Essential (9): histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine. You cannot make them.
- Non-essential (11): alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, proline, serine and tyrosine. Your body makes these itself.
There is a third group: the conditionally essential amino acids. These are arginine, cysteine, glutamine, tyrosine, glycine, proline and serine. You normally make them, but during illness or stress you may fall short 1.
BCAAs: 3 of the 9
Leucine, isoleucine and valine form a group of their own: the branched-chain amino acids, or BCAAs. They account for around 25% of the amino acids in foods with complete protein 2.
They have two particular features. Muscle can use them directly as energy during exercise. And leucine, above all, can stimulate protein synthesis in the muscle you have trained 2.
Lysine in protein
Cereals are short of lysine
Where to find them
In all the protein you eat, but not in the same proportions. An analysis of commercial protein isolates measured them 3:
| Protein | Essential amino acids (% of protein) | Leucine (% of protein) |
|---|---|---|
| Whey | 43% | 11.0% |
| Casein | 34% | 8.0% |
| Egg | 32% | 7.0% |
| Average of animal proteins | 37% | 8.8% |
| Average of plant proteins | 26% | 7.1% |
| Human muscle, for reference | 38% | 7.6% |
Source: Gorissen et al., 2018. Analysis of commercial protein isolates.
Three ideas come out of these data:
- Animal protein is richer in essential amino acids. On average they make up 37% of its protein, compared with 26% in plant protein. Whey protein reaches 43% 3.
- Cereals are short of lysine. Wheat protein has 1.4% and maize protein 1.5%. Animal protein has 7% on average 3.
- Many plant proteins are short of methionine. 1% on average, compared with 2.5% in animal protein 3.
That is why plant proteins complement each other. Brown rice protein is low in lysine (2.4%) but not in methionine; pea protein is the opposite (0.4% methionine) 3. Together they cover each other.
And you do not need to put them on the same plate: what counts is the balance over the day. What is not enough is a diet based on a single plant food 1.
An interesting detail: of the plant proteins analysed, potato protein was the only one that met the requirements for every essential amino acid on its own 3.
Why they matter if you exercise
To build muscle you need all 9. BCAAs alone already send the signal. In a trial with 10 trained men, 5.6 g of BCAAs after strength training raised muscle protein synthesis by 22% compared with placebo 5. But the authors conclude that, for the maximum response, the full set of essential amino acids is probably needed 5.
That is why the International Society of Sports Nutrition (ISSN) recommends servings of 20-40 g of protein. Each one should provide 700-3,000 mg of leucine and all the essential amino acids in good proportions 4. It also advises prioritising protein foods that contain all 9 4.
If you eat plant protein, bear this in mind: you need a little more to reach the same amount of leucine 3.
| Protein | Grams needed |
|---|---|
| Maize | 20 g |
| Potato | 33 g |
| Brown rice | 37 g |
| Pea | 38 g |
| Soya | 40 g |
| Wheat | 45 g |
| Oat | 47 g |
Source: Gorissen et al., 2018.
Total protein a day
How much protein a day: the reference and if you exercise
How many you need
EFSA has not set daily amounts for each essential amino acid in adults, because it considers that precise data are lacking 6. What it does set is total protein: 0.83 g per kg of body weight a day for adults 6. If you exercise, the ISSN considers 1.4-2.0 g per kg sufficient 4.
In practice: if you reach your protein target with a variety of sources, you cover the essential amino acids. How much do you need? We explain it in how much protein a day, or work it out with the protein calculator.
How to cover them day to day
- Include protein at every meal: meat, fish, eggs, dairy, pulses or soya.
- Spread it out: the ISSN advises distributing your protein servings evenly, every 3-4 hours 4.
- If you do not eat meat or fish, vary your plant sources over the day. And allow for a little more protein to reach the same amount of leucine 3.
- Use supplements as support, alongside your food. According to the ISSN, they are a practical way to make sure you get enough protein of good quality 4.
And supplements
- Protein powder: provides all 9 essential amino acids.
- BCAAs: provide 3 of the 9, with leucine in the leading role. They complement protein rather than replace it, and they make a practical drink for your training sessions. In 18 trials they were also associated with less muscle soreness between 24 and 96 hours after exercise. We explain it in BCAAs and leucine: what the studies say.
Not sure which to choose? We compare them in BCAAs or protein.
Frequently asked questions
What are the 9 essential amino acids?
Histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine. Your body cannot make them, so they have to come from food.
Which foods contain all the essential amino acids?
Animal proteins contain all of them in good proportions: meat, fish, eggs and dairy. Among plant proteins, soya comes very close, and by combining cereals and pulses over the day you cover them too.
Do you have to combine pulses and cereals in the same meal?
No. According to the US National Library of Medicine, you do not need to get every amino acid at each meal: what counts is the balance over the whole day.
Are BCAAs essential amino acids?
Yes. BCAAs are 3 of the 9 essential amino acids: leucine, isoleucine and valine. They account for around 25% of the amino acids in complete proteins.
Sources
- MedlinePlus, U.S. National Library of Medicine. Amino acids. Reviewed 21 January 2025. View publication
- Office of Dietary Supplements, National Institutes of Health. Dietary supplements for exercise and athletic performance: fact sheet for health professionals. View publication
- Gorissen SHM, Crombag JJR, Senden JMG, Waterval WAH, Bierau J, Verdijk LB, van Loon LJC. Protein content and amino acid composition of commercially available plant-based protein isolates. Amino Acids. 2018;50(12):1685-1695. View publication
- Jäger R, Kerksick CM, Campbell BI, et al. International Society of Sports Nutrition position stand: protein and exercise. J Int Soc Sports Nutr. 2017;14:20. View publication
- Jackman SR, Witard OC, Philp A, Wallis GA, Baar K, Tipton KD. Branched-chain amino acid ingestion stimulates muscle myofibrillar protein synthesis following resistance exercise in humans. Front Physiol. 2017;8:390. View publication
- EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA). Scientific opinion on dietary reference values for protein. EFSA Journal. 2012;10(2):2557. View publication
Information based on published studies. It does not replace the advice of a doctor or registered dietitian. The results describe what was measured in each study, not the properties of any specific product. A varied and balanced diet and a healthy lifestyle are important.
