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Amino Acids (An Overview)

Updated: Aug 15

Evidence-Based. Scientifically Reviewed by Michael Sharpe, MSc.

Amino acids, often known as protein building blocks, are chemicals that perform a variety of important functions in your body.

They're required for essential activities including protein synthesis and hormone and neurotransmitter production. Some may also be used as a supplement to enhance athletic performance or improve mood in a natural manner.

Several criteria determine whether they are essential, conditionally necessary, or nonessential.

This page covers all you need to know about essential amino acids, including how they work, where you can get them, and why you should take a supplement.

Table of Contents:

man pouring amino acid pills into his hand

Essential Amino Acids

Amino acids are organic molecules that are made up of nitrogen, carbon, hydrogen, oxygen, and a variable side chain group.

To develop and operate correctly, your body need 20 different amino acids. Only nine amino acids are designated as essential, although all 20 amino acids are important in one way or another.

  • Histidine

  • Isoleucine

  • Leucine

  • Lysine

  • Methionine

  • Phenylalanine

  • Threonine

  • Tryptophan

  • Valine

These nine are essential amino acids (EAAs), unlike nonessential amino acids, they cannot be produced by the body and must be acquired via food.

Animal proteins, such as meat, eggs, and poultry, are the greatest suppliers of necessary amino acids.

When you consume protein, it's broken down into amino acids, which are then utilised by your body to assist with activities like muscle development and immune function regulation (2Trusted Source).

Conditionally Essential Amino Acids

Conditionally necessary amino acids include a number of non-essential amino acids which are only deemed necessary under certain situations, such as when you are ill or under stress.

Arginine, for example, is deemed non-essential, yet your body cannot fulfil demands while battling illnesses.

As a result, arginine must be supplemented via food in some circumstances to fulfil your body's requirements.

Branched Chain Amino Acids

The branched-chain amino acids (BCAAs) are three of the nine essential amino acids.

  • Leucine

  • Isoleucine

  • Valine

The molecular structure of BCAAs, which are present in protein-rich foods including eggs, meat, and dairy products, is referred to as "branched-chain".

BCAAs are well-known in the bodybuilding and fitness community and are commonly thought of as being able to increase muscle growth.

What They Do

Essential amino acids are involved in a variety of important functions. Though amino acids are well known for their function in muscle growth and repair, the body needs them for a lot more.

That's why a lack of necessary amino acids may harm your body, including your neurological, reproductive, immunological, and digestive systems.

Each of the nine essential amino acids has a different function in your body. They help in tissue development, energy generation, immunological function, food absorption, among other things.

The nine essential amino acids serve a variety of functions within your body, such as the following.


Histidine is a building block for histamine, a neurotransmitter involved in immune response, digestion, sexual function, and sleep-wake cycles.

It's necessary for the myelin sheath, a protective barrier that covers your nerve cells, to remain intact. (1)


Isoleucine: The third and final branched-chain amino acid, isoleucine plays a role in muscle metabolism and is found in high concentration in muscle tissue.

Immune function, haemoglobin synthesis, and energy control are all dependent on it. (2)


Leucine is a branched-chain amino acid that, like valine, is essential for protein synthesis and muscle repair.

It also aids in blood sugar regulation, wound healing, and the production of growth hormones. (3)


Lysine plays an important function in protein synthesis, hormone and enzyme production, and calcium absorption.

It's also necessary for energy generation, immunological function, and collagen and elastin synthesis. (4)


Methionine is a necessary component of metabolism and detoxification. It's also required for tissue development and the absorption of zinc and selenium, all of which are essential elements for good health. (5)


Phenylalanine is a precursor of tyrosine, dopamine, epinephrine, and norepinephrine, which are all neurotransmitters.

It is essential for the structure and function of proteins and enzymes, as well as the synthesis of other amino acids. (6)


Threonine is a key component of structural proteins like collagen and elastin, which are crucial components of the skin and connective tissue.

It also helps with fat metabolism and immune system function. (7)


Tryptophan: Despite its reputation for inducing sleepiness, tryptophan serves a variety of other purposes.

It is a precursor of serotonin, a neurotransmitter that controls your appetite, sleep, and mood, and is required to maintain correct nitrogen balance. (8)


Valine is one of three branched-chain amino acids, which means that one of its chains branches out to one side of its molecular structure.

Valine is involved in energy production and helps to promote muscle development and repair. (9)

Benefits of Taking Essential Amino Acids

While necessary amino acids may be found in a variety of meals, supplementing with higher amounts has been linked to a number of benefits, as described below.

Improves Exercise Performance

The three branched-chain essential amino acids are often utilised to reduce tiredness, enhance athletic performance, and promote muscle repair after exercise.

Supplementing with branched-chain amino acids was shown to be better at improving muscle repair and decreasing soreness after intense exercise than rest alone. (10)

When compared to a placebo, branched-chain amino acid supplements enhanced performance, muscular repair, and reduced muscle pain in 16 resistance-trained athletes. (11)

Taking 4 grams of leucine per day for 12 weeks improved strength performance in untrained individuals, demonstrating that necessary amino acids may help non-athletes as well. (12)

Prevents Muscle Loss

Muscle loss is a frequent side effect of long-term sickness and bed rest, particularly in the elderly.

It has been discovered that essential amino acids help to prevent muscle breakdown and maintain lean body mass.

In a 10-day trial of 22 older people on bed rest, those who got 15 grammes of mixed essential amino acids maintained muscle protein synthesis, whereas those who received a placebo had the process drop by 30%. (13)

Supplementing with essential amino acids has also been shown to help older individuals and sportsmen maintain lean body mass. (14, 15)

Increases Weight Loss

Branched-chain essential amino acids have been shown to be helpful in promoting fat reduction in humans and animals in certain research.

For example, a study of 36 strength-trained men showed that supplementing with 14 grammes of branched-chain amino acids per day reduced body fat percentage considerably more than whey protein or a sports drink during an eight-week period. (16)

A meal containing 4% extra leucine decreased body weight and fat in rats, according to a research. (17)

Other research on the possible link between branched-chain amino acids and weight loss, on the other hand, has proven inconclusive.

More research is required to see whether these amino acids may help people lose weight. (18, 19)

Taking necessary amino acid supplements may assist with mood, athletic performance, muscle loss prevention, and weight reduction.

May Improve Mood & Sleep

Serotonin, a molecule that functions as a neurotransmitter in your body, requires tryptophan to be produced.

Serotonin is a neurotransmitter that regulates mood, sleep, and behaviour.

While low serotonin levels have been related to depression and sleep problems, many studies have indicated that taking tryptophan supplements may help alleviate depression symptoms, enhance mood, and improve sleep. (20, 21, 22)

In a 19-day research involving 60 older women, 1 gramme of tryptophan per day resulted in enhanced energy and pleasure when compared to a placebo. (23)

Dietary Sources

Because your body is unable of producing essential amino acids, you must get them via your diet.

Many foods are high in essential amino acids, making it simple to fulfil your daily requirements.

Sources of complete protein include the following.

  • Dairy

  • Meat

  • Seafood

  • Poultry

  • Eggs

Plant-based foods like soy, quinoa, and buckwheat provide all nine necessary amino acids, making them complete protein sources. (24)

Beans and nuts, for example, are considered inadequate protein sources because they lack one or more necessary amino acids.

Provided you adopt a plant-based diet, however, you may still get enough of all necessary amino acids if you consume a variety of plant proteins every day.

Even if you want to avoid animal products, selecting a range of incomplete proteins such as beans, nuts, seeds, whole grains, and vegetables may guarantee that your essential amino acid requirements are fulfilled.

Complete proteins may be found in both animal and plant sources, such as meat, eggs, quinoa, and soy.

Recommended Daily Intake

The nine essential amino acids' recommended daily allowance per 2.2 pounds (1 kg) of body weight are given below.

  • Histidine: 14 mg

  • Isoleucine: 19 mg

  • Leucine: 42 mg

  • Lysine: 38 mg

  • Methionine (+ the non-essential amino acid cysteine): 19 mg

  • Phenylalanine (+ the non-essential amino acid tyrosine): 33 mg

  • Threonine: 20 mg

  • Tryptophan: 5 mg

  • Valine: 24 mg


This section contains links to research, studies, and sources of information for this article, as well as authors, contributors, etc. All sources, along with the article and facts, are subjected to a series of quality, reliability, and relevance checks.

Real Muscle primarily uses high-quality sources, such as peer-reviewed publications, to back up the information in our articles. To understand more about how we fact-check and keep our information accurate, dependable, and trustworthy, read more about us.

This evidence based overview of amino acids features 24 references, listed below.

1. PubChem Compound Summary for CID 6274, Histidine. ✔

2. PubChem Compound Summary for CID 6306, l-Isoleucine. ✔

3. PubChem Compound Summary for CID 6106, Leucine. ✔

4. PubChem Compound Summary for CID 16130064, L-Lysine.

5. PubChem Compound Summary for CID 6137, Methionine.

6. PubChem Compound Summary for CID 6140, Phenylalanine.

7. PubChem Compound Summary for CID 6288, l-Threonine.

8. PubChem Compound Summary for CID 54608559, L-Tryptophan. ✔

9. PubChem Compound Summary for CID 6287, Valine.

10. Rahimi MH, Shab-Bidar S, Mollahosseini M, Djafarian K. Branched-chain amino acid supplementation and exercise-induced muscle damage in exercise recovery: A meta-analysis of randomized clinical trials. Nutrition. (2017, Oct) (Meta-Analysis)

11. Waldron M, Whelan K, Jeffries O, Burt D, Howe L, Patterson SD. The effects of acute branched-chain amino acid supplementation on recovery from a single bout of hypertrophy exercise in resistance-trained athletes. Appl Physiol Nutr Metab. (2017, Jun) (Randomised Controlled Trial)

12. Ispoglou T, King RF, Polman RC, Zanker C. Daily L-leucine supplementation in novice trainees during a 12-week weight training program. Int J Sports Physiol Perform. (2011, Mar) (Controlled Clinical Trial)

13. Ferrando AA, Paddon-Jones D, Hays NP, Kortebein P, Ronsen O, Williams RH, McComb A, Symons TB, Wolfe RR, Evans W. EAA supplementation to increase nitrogen intake improves muscle function during bed rest in the elderly. Clin Nutr. (2010, Feb)

14. Dillon EL, Sheffield-Moore M, Paddon-Jones D, Gilkison C, Sanford AP, Casperson SL, Jiang J, Chinkes DL, Urban RJ. Amino acid supplementation increases lean body mass, basal muscle protein synthesis, and insulin-like growth factor-I expression in older women. J Clin Endocrinol Metab. (2009, May)

15. Dudgeon WD, Kelley EP, Scheett TP. In a single-blind, matched group design: branched-chain amino acid supplementation and resistance training maintains lean body mass during a caloric restricted diet. J Int Soc Sports Nutr. (2016, Jan 5) (Randomised Controlled Trial)

16. Stoppani J, Scheett T, Pena J, Rudolph C, Charlebois D. 2009 international society of sports nutrition conference and expo new orleans, la, USA. 14-15 june 2009. Abstracts. J Int Soc Sports Nutr. (2009, Jul 31)

17. Vianna D, Resende GF, Torres-Leal FL, Pantaleão LC, Donato J Jr, Tirapegui J. Long-term leucine supplementation reduces fat mass gain without changing body protein status of aging rats. Nutrition. (2012, Feb).

18. Leenders M, Verdijk LB, van der Hoeven L, van Kranenburg J, Hartgens F, Wodzig WK, Saris WH, van Loon LJ. Prolonged leucine supplementation does not augment muscle mass or affect glycemic control in elderly type 2 diabetic men. J Nutr. (2011, Jun) (Randomised Controlled Trial)

19. Baum JI, Washington TA, Shouse SA, Bottje W, Dridi S, Davis G, Smith D. Leucine supplementation at the onset of high-fat feeding does not prevent weight gain or improve glycemic regulation in male Sprague-Dawley rats. J Physiol Biochem. (2016, Dec)✔

20. Jenkins TA, Nguyen JC, Polglaze KE, Bertrand PP. Influence of Tryptophan and Serotonin on Mood and Cognition with a Possible Role of the Gut-Brain Axis. Nutrients. (2016, Jan 20) (Review)

21. Markus CR, Firk C, Gerhardt C, Kloek J, Smolders GF. Effect of different tryptophan sources on amino acids availability to the brain and mood in healthy volunteers. Psychopharmacology (Berl). (2008, Nov) (Randomised Controlled Trial)

22. Parker G, Brotchie H. Mood effects of the amino acids tryptophan and tyrosine: 'Food for Thought' III. Acta Psychiatr Scand. (2011, Dec) (Review)

23. Mohajeri MH, Wittwer J, Vargas K, Hogan E, Holmes A, Rogers PJ, Goralczyk R, Gibson EL. Chronic treatment with a tryptophan-rich protein hydrolysate improves emotional processing, mental energy levels and reaction time in middle-aged women. Br J Nutr. (2015, Jan 28) (Randomised Controlled Trial)

24. Michelfelder AJ. Soy: a complete source of protein. Am Fam Physician. (2009, Jan 1)

Citations with a tick indicate the information is from a trusted source.


The information provided in this article is not intended to replace professional medical advice, diagnosis, or treatment. Always seek the guidance of a physician or other competent professional before following advice or taking any supplement. See our terms and conditions.

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