The 20 Amino Acids and Their Functio
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amino acids functions and what food rich in this amino acids.

The 20 Amino Acids and Their Functions

The amino acids are organic compounds formed by carboxyls and amines. These compounds bind to form proteins and other macromolecules. They are divided into two groups: essential and non-essential.

Essential amino acids are those that can not be synthesized by the human body autonomously. For this reason, this type of amino acid must be ingested through food.

Foods with the highest content of essential amino acids are meats (including fish), eggs, dairy products, nuts and some vegetables.

For their part, non-essential amino acids are those that can be produced by the human body (specifically by the liver) without the help of external agents.

In general terms, the functions of amino acids are as follows:

1-Regulate the sleep cycle and wakefulness.

2-Synthesizing hormones.

3-Stimulate the synthesis of muscle proteins.

4-Improve the circulation of oxygen in the muscles.

5-Regulate brain activity (such as alertness and feelings of depression)

6-Produce and store energy.

7-The essential amino acids are eight: phenylalanine, tryptophan, lysine, methionine, threonine, isoleucine, leucine and valine.

The non-essential amino acids are 12: glycine, alanine, serine, cysteine, aspartic acid, glutamic acid, asparagine, glutamine, arginine, tyrosine, proline and histidine.

The 20 amino acids and their main functions

1- Phenylalanine

Phenylalanine is an amino acid found in three forms: L-phenylalanine (naturally synthesized), D-phenylalanine (artificially synthesized) and DL-phenylalanine (a mixture of the two above).

Phenylalanine is necessary for the formation of chemicals used by the brain (neurotransmitters and hormones), such as  dopamine, noradrenaline y adrenalin.  Similarly, phenylalanine is involved in the formation of thyroid hormones.

Phenylalanine deficiency can lead to depression, loss of appetite, cognitive problems (confusion, loss of memory), lack of energy, decreased alertness, among others.

Some foods rich in this amino acid are beef, pork and fish, eggs, yogurt , cheese, soy products and some nuts.


Tryptophan helps in the formation of serotonin and melatonin, substances that regulate the sleep cycle. For this reason, said amino acid is used in pharmaceuticals antidepressants and in sedative and hypnotic pills.

It also intervenes in tolerance to pain, so it is used by athletes who undergo intense physical activities. Further, improves concentration. The deficit of this amino acid generates insomnia, depression and weight loss. 

Foods rich in tryptophan are turkey, chicken, beef, fish, soy grains, rice, some nuts and cheese.


Lysine intervenes in the formation of L-carnitine, which is a compound that allows the circulation of oxygen in muscle tissues. Lysine is involved in the metabolism of lipids, making them used as an energy source.

It also promotes the development of the immune system (thanks to the creation of antibodies), it is involved in the formation of hormones, enzymes and collagen (protein that creates bones, cartilage and connective tissues).

Foods rich in lysine are fish, eggs, cheese, soy grains, potatoes, yeast and dairy.


Methionine is involved in metabolism and helps to burn fat, and to the formation of other amino acids, such as cysteine and glutamine. It is used in the control of some pathogenic bacteria and to treat stones in the kidneys.

Other functions of this amino acid are reducing fat in the liver and muscle degeneration, keeping skin and nails healthy. The deficiency of methionine can lead to fat accumulation in the liver.

Some sources of methionine are lentils, red meats, fish, garlic, onions, eggs, yogurt, soy grains and some seeds.


Threonine is involved in the formation of vitamin B12. On the other hand, it promotes digestion and prevents diseases of the liver (since it helps to lower the cholesterol level in that organ and in the blood).

Intervenes in the regeneration of collagen proteins and helps the body to recover from wounds at muscle level.

Foods that are a source of threonine are meats, grains, dairy products, mushrooms and truffles, and vegetables.

6- Isoleucine

Along with leucine and valine, isoleucine is important for protein development and for energy storage. It helps the body to recover after having performed intense physical activities.

In addition, isoleucine is necessary for the synthesis of hemoglobin and is one of the main elements of red cells. Isoleucine deficiency produces symptoms similar to those of hypoglycaemia.

Foods that are sources of isoleucine are seeds, nuts, red meats (lamb, pork and beef), fish (especially tuna), lentils, soybeans, dairy pecorino cheese and parmesan) and eggs.

7- Leucine

Leucine is important in the formation of muscle tissue, it helps maintain that tissue once it has been formed and is necessary to maintain nitrogen balance in the body.

In addition, leucine benefits the rebuilding of muscle tissues, skin and bones.

Foods rich in leucine are grains (soybeans, lentils and chickpeas), nuts (peanuts, walnuts and almonds), red meat (especially pork and beef), marine products salmon, crustaceans and shrimp), eggs and dairy.


Valine is the amino acid that promotes tissue repair. It participates in energy storage, regulates the level of sugar in the blood and contributes to the process of growth and development of the human body.

Because of its restorative properties and energy storage, valine is one of the most important amino acids for athletes, so they consume it as supplements (in shakes, in pills, among others). It is possible to emphasize that the excess of valine in the body generates hallucinations.

Foods with higher levels of valine are meats, dairy, soy, peanuts and mushrooms.

9- Glycine

Glycine is the second most common amino acid in the human body. It forms part of the hemoglobin structure and is one of the major inhibitory neurotransmitters in the human body.

On the other hand, it is related to the production of glycogen and is involved in the suppression of the desire to ingest sugar and is part of the enzymes responsible for producing energy.

Finally, glycine transforms toxic substances into the body into non-harmful substances.

People with hypoglycemia, anemia, chronic fatigue syndrome and viral infections are deficient in this amino acid.

10- Alanine

Alanine is one of the main sources of energy for muscles and one of the most important amino acids involved in sugar metabolism.

It helps in the production of antibodies, which strengthens the immune system and is part of the connective tissues of the body.

Alanine deficiency is seen in people with hypoglycemia, fatigue, levels of viral infections, and elevated insulin levels.


Serine helps maintain blood sugar levels. Intervenes in the creation of antibodies, so it helps to strengthen the immune system, promotes the growth of muscle tissue and helps maintain it.

Other functions include fat metabolism and brain protein formation.


Cysteine is an antioxidant. Protects the human body against ultraviolet rays, radiation and pollution. Also, this amino acid plays an important role in the metabolism of some enzymes.

On the other hand, it involves repairing the skin tissue and keeping it healthy. It is one of the main components of hair.

13- Aspartic acid

The main function of aspartic acid is to generate resistance. This amino acid is involved in the metabolism of deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).

Other functions include protecting the liver (eliminating excess ammonia) and boosting the immune system (through the creation of antibodies).

The deficiency of aspartic acid in the human body generates the decrease of the levels of calcium and magnesium.

14- Glutamic acid

Glutamic acid is one of the most important amino acids among non-essential amino acids. This is responsible for the transport of glutamamine and other amino acids through the blood.

The presence of this molecule decreases the need to consume sugar and alcoholic beverages. It also increases energy levels in the human body.

Other functions are to accelerate the healing process of wounds and ulcers, and to aid in the synthesis of DNA.

The excess of this amino acid in the brain tissue can generate cellular damage. It is considered that during the cardivascular accidents the brain releases large amounts of this acid thus damaging the neurons.


Asparagine helps to remove ammonia from the body, increases resilience, decreases fatigue, detoxifies the body of harmful chemicals and intervenes in DNA synthesis.

It is found in large concentrations in the hippocampus and in the hypothalamus. It is necessary to maintain the homeostatic balance in the nervous system and plays an essential role in the short term memory. 

16- Glutamine

Glutamine is important as it keeps the blood sugar level. It maintains the strength of the muscles and makes them able to withstand intense physical activities.

On the other hand, glutamine is important for the functioning of the digestive system. The small intestine uses glutamine as the primary source of energy, being the only organ in the human body to do so. This amino acid is also involved in DNA synthesis.

Glutamine deficiency is seen in people with chronic fatigue syndrome, alcoholism and anxiety.

17- Arginine

Arginine is essential for the immune system to function properly. It also intervenes in wound healing, regeneration of the liver and increases insulin release.

This amino acid is necessary for the production and release of growth hormones.

The deficiency of this amino acid generates muscle weakness, hair loss, skin irritations and slow healing of wounds.

18- Tyrosine

Tyrosine reduces appetite, therefore, helps to reduce adipose tissue. It increases energy levels and intervenes in mental processes, improving concentration and reasoning ability.

This amino acid is precursor of the neurotransmitters dopamine, adrenaline, noradrenaline and melanin. It is used as an antidepressant.

Tyrosine deficiency can lead to depression, chronic fatigue syndrome, and hypothyroidism. The parkinson's disease and drug addiction are also related to the deficiency of this amino acid.


Proline affects nutrition in humans and is involved in the formation of cartilage . This amino acid is believed to act as a source of nitrogen.

Therefore, it is important to maintain the health of joints, tendons and ligaments.

Another function of this amino acid is to keep the heart strong and healthy. It also works together with vitamin C to protect the skin.


This amino acid is essential in some stages of human development, for example: during childhood. For this reason, it is called semi-essential, since it is only required in special circumstances.

Histidine is involved in the formation of hemoglobin, which is why it is used to treat anemia. It is also used to treat rheumatoid arthritis and some allergies. It also helps maintain pH in the blood.

Histidine deficiency can cause skin diseases, and cognitive and speech problems in children. For its part, the excess of this amino acid reduces the level of zinc.