What are the 8 Essential Amino Acids?

The eight essential amino acids are phenylalanine, valine, threonine, tryptophan, isoleucine, methionine, leucine and lysine. They are called essential amino acids not because they are more important than other substances but because it is essential that they are included in the daily diet since they are not produced naturally by the body.

1. Phenylalanine

Phenylalanine is an important component in the production of L-tyrosine, dopamine which is an anti-depressant, norepinephrine, epinephrine and the skin pigment, melanin. It is also a precursor of phenylethylamine, a popular anti-depressant dietary supplement.

There are three forms of phenylalanine: L-phenylalanine, D-phenylalanine and DL-phenylalanine.

L-phenylalanine is converted to L-tyrosine, then to L-DOPA and to dopamine.

D-phenylalanine produces endorphins and released by the pituitary glands during exercise, excitement, orgasm, when experiencing pain and after eating spicy food.

DL-phenylalanine is sold as a nutritional supplement to assert its analgesic and antidepressant characteristics. Its ability to relieve pain can be attributed to the ability of D-phenylalanine to block the enzyme carboxypeptidase to cause enkephalin damage.

Role of DL-phenylalanine in the body

DL-phenylalanine relieves pain and fights depression. Its pain-relieving properties can be attributed to its ability to block the enzyme carboxypeptidase that causes enkephalin damage.

2. Valine

Valine is a branched-chain amino acid like leucine and isoleucine. It is named after a plant called valerian. Foods rich in valine include cottage cheese, fish, poultry, peanuts, sesame seeds and lentils.

Together with leucine and isoleucine, valine belongs to the group of proteinogenic amino acids, building blocks of proteins that are produced by cells that are recorded in the genetic code of each living thing.

3. Threonine

Threonine, like valine and phenylalanine is not produced by the body, therefore it has to be taken through the food we eat.

Threonine is an important ingredient in the formation of bones and cartilages, hair teeth and nails. The mucin content in threonine, serine and proline which account for 20% to 55% of the total amino acid content in the intestines is responsible for this activity. This characteristic of threonine makes it a perfect ingredient for most gel-like preparations and lubricants.

Threonine can be found in abundance in cottage cheese, milk, eggs, sesame seeds, beans, poultry, fish, meat, lentils, corn, and various grains.

Role of threonine

The threonine content in the diet is responsible for the growth and development of liver muscles, skeletal muscles and small intestines of young animals.

Threonine may also prevent cancer. This occurs during the process of phosphorylation which usually occurs on threonine, serine, and tyrosine residues.

4. Tryptophan

Tryptophan is a sleep-inducing amino acid which is an important component in the production of serotonin, vitamin B3 or niacin, and auxin (a plant hormone).

It is the tryptophan content found in milk, chocolates, oats, bananas, dried dates, cottage cheese, turkey and peanuts that induces us to sleep. This is attributed to the high serotonin, (a neurotransmitter that calms the brain) and high melatonin (a sleep-inducing hormone) levels in the brain when a substantial amount of tryptophan-containing foods have been eaten.

The "feel-good" hormone serotonin sets you in a good mood, stops you from oversleeping and prevents you from feeling depressed. It is this property of serotonin that makes it a popular treatment for anxiety and depression. Another sleep-inducing hormone is melatonin which is produced in large quantities when there is no sunlight. This explains why, according to statistics, so many people go into deep depression, some of them committing suicide during winter time.

Role of tryptophan

Tryptophan is also used to treat seasonal affective disorder or SAD and premenstrual disorder, diseases associated with low levels of serotonin in the brain. Seasonal affective disorder is the term that refers to the winter blues experienced by some people which manifests through extremely low levels of serotonin and melatonin caused by the absence of sunlight during the gloomy winter months.

5. Isoleucine

Isoleucine is not synthesized by the body thus it has to be included in the diet. It is one of the proteinogenic amino acids, protein building amino acids produced by cells whose genetic information are contained in the genetic code.

It regulates blood sugar and boosts the body's energy levels. It plays a key role in the transport of oxygen from the lungs to the various parts of the body and the production of hemoglobin, the iron-containing part of the blood.

6. Methionine

Together with cysteine, methionine is one of two sulfur-containing proteinogenic amino acids. Methionine is an intermediate in the biosynthesis of cysteine, carnitine, taurine, lecithin, phosphatidylcholine, and other phospholipids. Improper conversion of methionine can lead to atherosclerosis.

Like its sulfur-containing pair cysteine, methionine also serves as an effective antioxidant and helps in body metabolism in the cellular level. It is a perfect scavenging agent against oxidative stress due to its ability to be converted to methionine sulfoxide. It is important because it can provide the body with the sulfur and methyl elements essential for human growth.

Role of methionine

It is used to treat diseases of the liver especially those caused by carbon tetrachloride and arsenic. Methionine is also known to possess the ability to minimize the spread of the flu virus by inhibiting their further proliferation in the body.

An overdose of methionine increases acidity of urine and causes the elimination of calcium from the body. This is the reason why this amino acid is given to dogs as a dietary supplement to protect damage to plants by reducing the pH level of the animal urine. Calcium supplementation is recommended to compensate for the lost amount of calcium in the body.

This amino acid is also used by plants for synthesis of ethylene. The process is known as the Yang Cycle or the methionine cycle.

7. Leucine

Leucine is not produced by the body naturally, therefore it has to be taken through the food we eat and dietary supplements. It is called a buffer protein because it has the ability to protect the body when it lacks iron and at the same time provides protection when leucine is becoming poisonous to the body.

Leucine is used to produce sterols, substances that resemble fats (popular example is cholesterol) and are found in the liver, adipose and muscles tissues, but many times more active in the muscle and adipose tissues. It is used as dietary supplement because it delays the deterioration of muscle tissues through the significant increase in the production of muscle proteins.

It is due to these characteristics that leucine is highly recommended as dietary supplement for athletes and body builders to increase their stamina and endurance. This also makes leucine an ideal dietary supplement for patients who are recovering from major surgical procedures or those who were subjected to serious trauma or extreme muscle pain.

An overdose of leucine can lead to Maple Syrup Urine Disease (MSUD), a disorder characterized by deficiency in keto hydrogenase complex that can cause the accumulation of leucine, isoleucine and valine in the blood and urine. It is called Maple Syrup Urine Disease because an infant suffering from MSUD has urine that smells much like maple syrup, thus the name of the disease which can cause delirium, neurologic disorders and death.

Role of leucine

Leucine can also be used for weight loss because it has the ability to dissolve visceral fat, the kind of fat found in the deepest layer of the skin that does not respond to the usual weight loss exercises or non-surgical procedures.

Leucine is a great energy source especially during intense athletic performance and other extreme physical activities. It protects you from getting tired easily during exercise and it regulates your glucose level.

8. Lysine

Lysine, like the rest of the essential amino acids, cannot be produced naturally by the body and must be taken through dietary intake and supplements. It is one of the essential building blocks of proteins.

Lysine is a key component in the production of hormones and enzymes and plays an important role in collagen production, a substance that is critical in bone, muscle, cartilage, and skin formation.

Lysine can be obtained by eating protein-rich foods like meat, fish, eggs, soybeans, poultry products, nuts and other dairy products. This amino acid may be taken as a supplement in the form of tablets, powder or injection.

Role of lysine

Lysine plays a key role in calcium absorption by reducing the amount of calcium being excreted in the urine. It promotes the growth of hair, nails, teeth and bones. It also prevents bone loss that leads to osteoporosis, though there's no evidence that lysine prevents osteoporosis. It also prevents the occurrence of herpes simplex infections, or cold sores, but again, further study has to be conducted to prove this claim.

Lysine is considered safe except for a few cases of abdominal cramps and diarrhea when taken in high doses. Patients suffering from cardiovascular diseases and those under medications must consult with a physician or health practitioner before taking lysine.

Lysine should be taken by athletes who engage in strenuous physical activities for stamina and endurance. Vegetarians need a bigger amount of lysine intake since vegetables, except for legumes, contain very minimal amount of lysine.

Continuous research is being conducted on the potential of lysine as an important component in muscle-building, reducing cholesterol level and speeding up recovery after surgery.