The Complete Guide to Amino Acids

Ask anyone who trains about protein and you'll usually get a confident answer. How much they eat, which powder they use, whether they have a shake straight after the gym. Yet if you ask what that protein is actually made of, things tend to go quiet.

Case in point, amino acids.

Amino acids are the building blocks of protein, the small molecules your body strings together to make everything from muscle fibre to the enzymes that digest your lunch. Every gram of protein you eat is really a collection of amino acids, and which ones it contains, in what amounts, shapes how useful that protein is to you.

If you already pay attention to your protein intake, you are thinking about amino acids too, even if you have never checked an amino acid profile. They are part of the protein in your breakfast and the shake you might have after training.

This comprehensive guide explains everything you need to know about amino acids, including the different types, what they do in the body, where to find them in food, how much you need, and the benefits they provide.

Key takeaways

• Amino acids are the building blocks of protein. Your body uses them to build and repair tissues, and to make proteins such as enzymes and antibodies.
• Nine amino acids are essential, meaning you must get them from food. Your body can make the others, although some become conditionally essential when demand exceeds production.
• Focus on getting enough protein for your activity level. Most people can meet their amino acid needs through a varied diet without tracking each one individually.
• A vegan diet can supply all nine essential amino acids. Include a variety of protein sources across the day, such as soya, pulses, grains, nuts and seeds.
• Leucine helps trigger muscle protein synthesis, but building new muscle protein requires all nine essential amino acids. BCAAs provide only three.
• Supplements can help close a gap in your diet. A complete protein powder is a convenient option when food alone makes it difficult to meet your protein needs.
• Total daily protein intake has more influence on muscle growth than precise supplement timing. Spread protein across your meals and build a routine you can maintain.
  

What are amino acids?

Amino acids are the molecules your body links together to make protein.

While more than 500 amino acids have been identified in nature, your body uses 20 different standard amino acids to build every protein it needs.

• 9 of these are categorised as essential. These must come from your diet as the body does not naturally produce them.
• 11 are classed as non-essential or conditional. These are produced by your body on its own.

Every amino acid shares the same basic frame. A central carbon atom holds an amino group, an acid group, and a side chain, and it's that side chain that makes each one different. Some are tiny. Some contain sulphur. Some are drawn to water. All these variables affect how the finished protein folds into shape.

Amino acids join together in chains, and the order they sit in is written into your genes. That sequence decides the shape of each protein and with it, the job it does. Protein makes up roughly 15–20% of your body weight, so there's a great deal of this going on.

Your body gets amino acids in two ways.

• It produces them itself.
• It obtains them from the rest of the protein you eat and by recycling existing body proteins.

During digestion, proteins are broken into smaller peptides and amino acids, which can be absorbed and used by the body. Our complete guide to digestive enzymes covers this stage in more detail.

Once absorbed, amino acids join what's known as the amino acid pool, a circulating supply your body draws on whenever it needs to build something. That demand never really switches off. Your body breaks down and rebuilds its own proteins around the clock, turning over somewhere in the region of 250–300g of protein a day in an adult. Most of it is recycled, and the protein you eat replaces what's lost.

What are the different types of amino acids?

Amino acids are grouped by whether your body can actually make them. There are three categories: essential, non-essential, and conditionally essential.

Essential amino acids

Essential amino acids are the nine your body has no way of producing, so they must come from food. If your diet runs short of any one of them for long enough, your body can't make the proteins that depend on it.

The daily requirements for essential amino acids, set by the World Health Organization, are smaller than most people expect. The figures below are minimums for a 70kg adult.

*Methionine figure includes cysteine; phenylalanine figure includes tyrosine. Source: WHO/FAO/UNU (2007), based on 39mg leucine per kg of body weight per day and equivalent values for each amino acid.

Leucine, isoleucine, and valine are also known as branched-chain amino acids, or BCAAs, after the forked shape of their side chains. They get a lot of attention in sports nutrition, and we'll come back to them in the supplements section.

Non-essential amino acids

 Non-essential amino acids can be made by the body under normal circumstances. They are also present in food, so dietary intake contributes alongside that internal production.

The 11 standard amino acids classed as non-essential are:

Some of these can become conditionally essential in particular circumstances. That is why you may see the same name discussed under more than one category.

Conditionally essential amino acids

Conditionally essential amino acids are those your body can usually produce itself, but may need to obtain in greater amounts from the diet under particular circumstances. During significant illness or injury, for example, the body’s requirements can exceed its ability to make enough. Some amino acids also become essential at certain stages of growth and development.

What do amino acids do, and what are their benefits?

Amino acids take part in almost every process in your body. It's worth separating two ideas before going further, though. What amino acids do as part of normal body function is one thing. Whether taking extra amino acids, beyond what a balanced diet provides, adds any benefit is a separate question, and usually a narrower one. The sections below cover the first and flag the second where it comes up.

Muscle growth and maintenance

Your muscles are constantly being rebuilt. Muscle protein synthesis lays down new muscle protein while muscle protein breakdown clears the old, and whether your muscles grow, hold steady or shrink depends on the balance between the two over weeks and months. Protein contributes to the growth and maintenance of muscle mass, and amino acids are the form in which it does that work.

Resistance training provides a stimulus for muscle adaptation, while adequate dietary protein supplies amino acids to support that response.

Leucine contributes to muscle growth and maintenance both as a building block of protein and as a signal that helps activate muscle protein synthesis. The International Society of Sports Nutrition recommends that a serving of protein provide 700mg–3g of leucine alongside a balanced supply of the other essential amino acids. The amount needed to maximise the response varies with factors such as age and the protein source.

Leucine’s signal depends on the availability of the other essential amino acids to build new muscle protein. A complete protein source supplies all nine, providing both the signal and the materials needed to support the process.

The response to protein can also change with age. Older muscle may become less sensitive to a given amount of protein, a phenomenon known as anabolic resistance. An analysis of studies in healthy older and younger men estimated that muscle protein synthesis reached a plateau at approximately 0.4g of protein per kilogram of body weight in older men, compared with 0.24g/kg in younger men. For someone weighing 75kg, those amounts equate to roughly 30g and 18g of protein respectively. These figures describe the response measured in the studies, rather than a fixed requirement for everyone at each meal.

Exercise recovery and tissue repair

Training causes small amounts of damage to muscle fibres, and the repair process that follows is part of how muscle adapts. That repair relies on amino acids, as does the ongoing maintenance of tendons, ligaments, skin and bone.

Collagen is a good illustration. It gives structure to all of those connective tissues, and it has an unusual make-up, rich in glycine, proline and hydroxyproline. Your body produces collagen continuously, using amino acids from the pool.

Recovery, though, depends on more than amino acids. Sleep, total energy intake, hydration and how your training is structured all play a part, and eating plenty of protein across the day does more for repair than any single amino acid taken in isolation. We cover the evidence in detail, including which supplements are worth considering and which aren't, in our guide to the best supplements for muscle recovery.

Other roles in the body

While muscle impacts are the most talked about benefit, amino acids are involved in a remarkable range of other work.

• Enzymes are proteins built from amino acids. Every chemical reaction your body depends on, from digesting food to producing energy, relies on them.
• Hormones such as insulin are proteins too. Others are built from a single amino acid: your thyroid hormones start life as tyrosine.
• Neurotransmitters, the chemical messengers of the brain and nervous system, often begin as amino acids. Tryptophan is converted into serotonin, which the body later uses to make melatonin. Tyrosine is the starting point for dopamine and noradrenaline. Glutamate and glycine act as neurotransmitters in their own right.
• Transport and immunity rely on proteins as well. Haemoglobin carries oxygen in your blood, and antibodies help your immune system recognise infections.
  

This is where the difference between normal function and supplementation is important. It's tempting to assume that eating more tryptophan means making more serotonin, but these pathways are tightly regulated, and amino acids compete with one another to cross into the brain. Knowing an amino acid is involved in a process doesn't mean taking more of it will change that process.

Which foods contain amino acids?

Any food that contains protein contains amino acids. Both animal and plant foods contribute, so there are plenty of ways to meet your needs without building every meal around the same ingredients.

Choose sources you enjoy and can prepare consistently. Your usual shopping basket is a better place to begin than an elaborate meal plan you are unlikely to follow.

Animal sources of amino acids

Animal foods provide complete protein, with all nine essential amino acids, and they tend to be rich in leucine. Useful everyday options include:

• Dairy – Greek yoghurt, cottage cheese, milk and cheese. Around 10g of protein in 100g of Greek yoghurt.
• Eggs – roughly 6–7g of protein per large egg, and an easy addition to most meals.
• Fish – salmon, tuna, cod and prawns, with around 20–25g of protein per 100g.
• Meat and poultry – chicken breast provides around 30g of protein per 100g cooked, with lean beef and turkey close behind.

Dairy proteins deserve a particular mention. Whey and casein, the two proteins in milk, score among the highest of any food for protein quality, and whey is especially high in leucine.

Plant-based sources of amino acids

Plant foods provide plenty of protein too, though amounts and amino acid profiles vary more.

• Soya – tofu, tempeh, edamame and soya milk. Soya is one of the few plant proteins that are complete on their own.
• Pulses – lentils, chickpeas, beans and peas, with around 7–9g of protein per 100g cooked. They're rich in lysine but lower in methionine.
• Nuts and seeds – peanuts, almonds, pumpkin seeds, and hemp seeds. Pumpkin and hemp seeds contain around 30g of protein per 100g, and a tablespoon or two adds up over the day.
• Grains – oats, wholegrain rice, and wholewheat bread contribute more than people expect, although they tend to be low in lysine. Quinoa and buckwheat are exceptions, providing complete protein.

Complete and incomplete proteins

A complete protein contains all nine essential amino acids in amounts that meet your body's needs. An incomplete protein is low in at least one. Whichever essential amino acid is in shortest supply is called the limiting amino acid, and it caps how much of that protein your body can put to use.

Most plant foods are incomplete on their own, but their gaps don't overlap. Pulses are short on methionine and well supplied with lysine, while grains are the reverse. Eat both and they cover for each other.

You may have come across the advice that people on plant-based diets need to combine proteins at every meal, rice with beans or hummus with pitta. The principle is sound, but the timing is stricter than it needs to be. Because your body draws from its amino acid pool, eating a variety of protein sources across the day is enough.

Protein quality is measured using the Digestible Indispensable Amino Acid Score, or DIAAS, recommended by the Food and Agriculture Organization of the United Nations since 2013. It rates proteins on both their essential amino acid profile and how well they're digested. Dairy, eggs and meat score highest. Individual plant proteins tend to score lower, and research on commercial plant protein isolates has found that blending them produces amino acid profiles much closer to animal sources.

How much protein do you need to get enough amino acids?

For most people, total protein intake is the most valuable number to focus on.

If you eat enough protein from reasonably varied sources, you'll meet your requirement for every essential amino acid without having to think about them individually.

How much that is depends on how active you are and what you're aiming for.

UK guidance sets the reference nutrient intake for protein at 0.75g per kg of body weight per day, around 53g for a 70kg adult. It's designed to cover the needs of almost everyone in the general population, so for anyone who trains regularly, it's best treated as a minimum.

For people doing resistance training, the evidence points higher. A 2018 meta-analysis of 49 trials, published in the British Journal of Sports Medicine, found that gains in muscle mass levelled off at around 1.6g of protein per kg per day, with some people benefiting up to about 2.2g/kg. The International Society of Sports Nutrition recommends 1.4–2.0g/kg for most people who exercise.

How you spread consumption across the day is also important. Around 20–40g of protein per meal, across three or four meals, supports muscle protein synthesis more consistently than most of the day's protein arriving at dinner. Older adults may benefit from the upper end of that range at each meal.

Do you need amino acid supplements?

If you're eating enough protein for your activity level, from complete sources or a varied mix of plant proteins, you're already getting every amino acid you need. For most people, that's the whole answer.

A supplement becomes worth considering if there's a gap you're finding hard to close with food. Some useful questions to ask yourself:

• Am I regularly falling short of my protein target?
• Is my appetite small, or am I eating less than usual?
• Do I avoid dairy, or follow a plant-based diet with limited protein variety?
• Am I older and finding it harder to get a meaningful amount of protein at each meal?
• Do I train fasted, or long enough that eating beforehand is impractical?

If none of these apply, extra amino acids are unlikely to add much. If one or two do, it's worth thinking about which kind of supplement fits.

Amino acid supplements vs protein powder

A protein powder provides a convenient source of dietary protein, which your body breaks down into amino acids during digestion. Choosing a complete protein powder supplies all nine essential amino acids and can help you meet your daily protein needs when food alone falls short.

Whey protein is naturally complete and high in leucine. Plant protein powders vary, and the best ones blend sources so their gaps cancel out. The Health Protein, for instance, combines pea protein, which is low in methionine, with brown rice protein, which is low in lysine, for a complete profile.

Grams of protein on a label only tell part of the story, so we publish the essential amino acid, BCAA and leucine content of each of our protein blends.

Each provides around 3g of leucine per serving, at the top of the range associated with maximising muscle protein synthesis.

Amino acid supplements, by contrast, provide individual amino acids without the rest of the protein. They're lighter, digest quickly and contain very few calories, which suits some situations. But they're a narrower tool, and for most people a protein powder does more of the job.

BCAAs vs EAAs: what's the difference?

BCAAs are three essential amino acids: leucine, isoleucine and valine. EAAs are all nine essential amino acids, including those three.

BCAAs supply only three of the nine essential amino acids needed to build muscle protein. A review by Wolfe (2017) explains that, without a dietary supply of the remaining six, the body must rely on existing amino acid pools and protein breakdown to provide them. This limits the ability of BCAAs alone to support net muscle protein gain. EAA supplements provide all nine essential amino acids, avoiding that particular limitation.

When should you take amino acid supplements?

Timing depends on the product and exactly why you are using it.

A meta-analysis on protein timing found no significant benefit for muscle growth or strength from consuming protein close to a workout after accounting for differences in total protein intake. Total protein intake was the strongest predictor of muscle growth in the analysis, suggesting that meeting your daily needs deserves more attention than getting the timing exactly right.

That said, some timings can make it easier to fit protein into your routine:

• Around training – a serving of protein or EAAs within a couple of hours either side of a session is a sensible habit, especially if you haven't eaten for a while.
• During long sessions – this is where BCAAs are most often used.
• Alongside low-protein meals – if breakfast or lunch tends to be light on protein, that's where a supplement can do the most good.

Treat timing as a way to make good intake easier, not as a substitute for it.

Are amino acid supplements safe?

For healthy adults, amino acid and protein supplements taken at the amounts used in research are generally well tolerated. The most common side effects are digestive, such as bloating or nausea, and are more likely at large doses.

A few groups should take more care. People with the inherited condition phenylketonuria (PKU) must avoid phenylalanine. If you're pregnant, breastfeeding, have a kidney or liver condition, or take regular medication, speak to your GP or pharmacist before starting a supplement. Very large doses of a single amino acid can also compete with others for absorption, so staying close to studied amounts is sensible.

Making sense of amino acids in your everyday diet

Amino acids can look complicated on paper, with twenty building blocks, three categories and a long list of jobs. Day to day, looking after them is fairly simple.

Eat enough protein for how active you are and spread it across your meals. Include complete sources where you can, or a varied mix of plant proteins if you don't eat animal products. As you get older, make sure each meal carries a worthwhile amount rather than saving most of it for the evening.

Supplements are there to fill gaps rather than replace food. For most people who train, a complete protein such as The Strong Protein, or The Health Protein on a plant-based diet, is the most useful place to start. It covers every essential amino acid in a single serving and fits easily around meals and training.

Frequently asked questions

How many amino acids are there?

There are more than 500 amino acids that exist in nature, but the human body uses 20 to build protein. Nine are essential and must come from food, and 11 are non-essential because your body can make them. Some scientists count selenocysteine as a 21st, as it appears in a small number of human proteins.

Does whey protein contain all nine essential amino acids?

Yes. Whey is a complete protein, containing all nine essential amino acids, and it's naturally high in leucine, the amino acid that signals muscle protein synthesis. A 40g serving of The Strong Protein, which combines whey and casein, provides 14g of essential amino acids and 3g of leucine.

Can you get enough amino acids on a vegan diet?

Yes. Soya, quinoa and buckwheat are complete proteins, and eating a variety of pulses, grains, nuts and seeds across the day covers all nine essential amino acids. Blended plant protein powders, such as those combining pea and brown rice, are designed to provide a complete profile in each serving.

Do you need BCAAs if you already take protein powder?

Usually not. A single serving of a quality protein powder already contains several grams of BCAAs, around 7g in a serving of The Strong Protein, alongside the other essential amino acids your muscles need. BCAAs are most often used during long training sessions rather than as a protein replacement.

References

• Kerksick, C. M. et al. (2017). International society of sports nutrition position stand: nutrient timing. Journal of the International Society of Sports Nutrition, 14, 33. Click here.
• Food and Agriculture Organization of the United Nations (FAO). (2013). Dietary protein quality evaluation in human nutrition: Report of an FAO Expert Consultation. FAO Food and Nutrition Paper 92. Rome: FAO. Click here.
• World Health Organization, Food and Agriculture Organization of the United Nations and United Nations University (WHO/FAO/UNU). (2007). Protein and amino acid requirements in human nutrition. WHO Technical Report Series, 935. Geneva: WHO. Click here.
• Morton, R. W. et al. (2018). 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. Click here
• British Journal of Sports Medicine, 52(6), 376–384. Click here.
• Jäger, R. et al. (2017). International Society of Sports Nutrition Position Stand: protein and exercise. Journal of the International Society of Sports Nutrition, 14, 20. Click here.
• Moore, D. R. et al. (2015). Protein ingestion to stimulate myofibrillar protein synthesis requires greater relative protein intakes in healthy older versus younger men. The Journals of Gerontology: Series A, 70(1), 57–62. Click here.
• Wolfe, R. R. (2017). Branched-chain amino acids and muscle protein synthesis in humans: myth or reality? Journal of the International Society of Sports Nutrition, 14, 30. Click here.
• Schoenfeld, B. J., Aragon, A. A. and Krieger, J. W. (2013). The effect of protein timing on muscle strength and hypertrophy: a meta-analysis. Journal of the International Society of Sports Nutrition, 10, 53. Click here.