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Essential Amino Acids: Definition, Benefits and Food Sources

Written by Resurchify | Updated on: April 20, 2022

Essential Amino Acids: Definition, Benefits and Food Sources

Amino acids are as popular as they are essential. Everybody knows what amino acids are, but it is necessary to go into detail about them and get to know their types and functions. There are a lot of different types of amino acids, but not all of them are essential. In this article, you will learn about their types and what role each of them plays in our bodies. So let's get started.

What Are Amino Acids?

Amino acids are building blocks of protein, and protein is the building block of life. So that makes amino acids the building blocks of life along with protein. When protein breaks down in our body, they form amino acids. Each amino acid comprises a unique R group with a primary amino group (-NH2 ) and an acidic carboxyl group. It is also called alpha-amino carboxylic acid. They differ from each other in the particular chemical structure of R.

Types of Amino Acids

There are twenty different types of Amino acids which are broadly classified into three categories:

Essential Amino Acids

There are nine essential amino acids that are as follows:

Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan, and Valine.

Our body doesn't produce these amino acids, so we have to consume them from the outside. Mostly, we get amino acids from animal meat, eggs, and poultry. Some soy plants like edamame and tofu contain these essential amino acids.

Non-essential Amino Acids

The naturally produced amino acids are non-essential. They are made inside our bodies, so there is no problem even if we don't get them from our food. The non-essential amino acids are:

Alanine, Arginine, Asparagine, Aspartic acid, Cysteine, Glutamic acid, Glutamine, Glycine, Proline, Serine, and Tyrosine.

These two categories comprise all amino acids. Still, some non-essential amino acids are essential at some point in time, like illness, pregnancy, infancy, stress, injury, trauma, etc. These non-essential amino acids are called Conditional Amino acids or Conditionally Essential Amino acids. These are:

Arginine, Cysteine, Glutamine, Tyrosine, Glycine, Ornithine, Proline, and Serine.

Essential Amino Acids

There are nine essential amino acids, and all of them have a specific role in body functioning.

Histidine

Histidine is an alpha-amino acid used in the biosynthesis of proteins. This amino acid helps in the growth of specific hormones and metabolites that have an influence on kidney function, the transmission of nerves, stomach secretions, and the immune system. It is effective in the repair and growth of tissues and in making blood cells. The amino acid produces histamine, a neurotransmitter vital for immune response, digestion, and the sleep-wake cycle. Histamine acts as an essential inflammatory agent for the immune system. 

Histidine is required for maintaining the Myelin Sheath, a protective barrier around nerve cells. It is a semi-essential amino acid that is not essential for adults but is essential for kids and infants, and people with a kidney disorder called Uremia. Uremia is a disorder where toxins buildups in your blood and can lead to serious health issues or even death. Histidine is also needed for the growth and development of plants, but plants are able to synthesize Histidine.

The most special thing about Histidine is the presence of a positively charged imidazole functional group which makes it a common participant in enzyme-catalyzed reactions. 

Histidinemia is caused by the deficiency of the enzyme that breaks down Histidine. The main food source for Histidine is meat, poultry, fish, dairy products, nuts, and whole grains like rice and wheat. The deficiency of Histidine may cause anaemia, chronic kidney failure, pneumonia, or specific psychiatric disorders. It is not a serious health problem. The recommended intake of Histidine is 10-14 mg/kg.

Phenylalanine

Our body uses phenylalanine for a variety of functions. It has an important role in the structure and function of proteins and enzymes. They also help in the production of other amino acids, a multi-tasking amino acid indeed. Phenylalanine is converted into Tyrosine by the body, which is essential for neurotransmission and production of brain chemicals like epinephrine, norepinephrine, and dopamine.

Tyrosine is mostly present in fluid form in all parts of the body. They help build protein in the body and produce enzymes, thyroid hormones, and melanin. It is effective in the treatment of skin disorders and depression. This amino acid is a direct relation to a person's mood and brain function.

There are two types of phenylalanine, L-phenylalanine and D-phenylalanine, both nearly identical but with different molecular structures. D-phenylalanine is not an essential amino acid. L-phenylalanine is the only form found in protein. Phenylalanine is most effective in the treatment of a skin disorder called vitiligo. A low level of phenylalanine can cause various depressive disorders. 

Soy products like soybean, tofu, seafood like salmon, trout, tuna, nuts, milk, eggs, and meat are some food high in phenylalanine. 25mg/kg is the ideal amount needed for an average adult. 

Phenylketonuria, also called PKU, is a rare inherited disorder that causes the build-up of phenylalanine in the human body. It causes decreased metabolism of phenylalanine. It is genetic, caused by a defect in the gene, and may lead to dangerous problems like seizures, intellectual disability, mental disorders, lighter skin, etc. People with phenylalanine have to follow a strict diet that restricts the intake of protein. It doesn't have a cure, so a person with PKU has to undergo regular medical checkups and treatment throughout life.

Lysine

Lysine is an essential amino acid responsible for the biosynthesis of protein. It has many uses ranging from calcium absorption to the production of hormones and enzymes. It is vital for the production of collagen. Collagen is the main structural protein in various connective tissues and is responsible for healthy joints and stretchiness. Collagen production also facilitates wound healing. In animal tissue, lysine becomes active at the site of the wound and aid with the repair process.

It is used to form carnitine which is found in most cells of the body. It protects against cold sores by blocking Arginine. Cold sores are infections that appear on the lip or corners of the mouth. Lysine reduces the duration and frequency of cold sores. Lysine is also effective in reducing stress-level and anxiety. It helps in the absorption of calcium and holds on to minerals in the kidney, preventing the loss of calcium through urine. 

Lack of lysine may lead to defective connective tissue, impaired fatty acid metabolism, anaemia, and protein-energy deficiency. Excess lysine may cause neurological disorders and ineffective metabolism.  Like other amino acids, the main food source for lysine are meat, dairy products, eggs, etc. apart from that, fenugreek seed, spirulina, and tofu are great sources for lysine. The maximum intake of lysine should be 30mg/kg.

Valine

Valine has a chain branching from one side of its molecular structure. It helps in muscle growth and regeneration, is involved in energy production and requires at least 20mg/kg daily. Deficiency may cause loss of muscle mass, growth failure, neuropathic obstacle, anaemia, and organ damage. It is synthesized by plants.

Diabetic humans have a higher level of valine in their blood. It is a precursor in the penicillin biosynthetic pathway. It has a wide application in the field of pharmaceutical and food industries. Valine enhances energy, increases endurance, and aids in muscle tissue recovery and growth. Thus, it is very helpful for athletes to boost their athletic performance. It is also helpful in reducing elevated sugar levels and increases growth hormone production. It is crucial for nitrogen balance in an adult and the growth of infants.

Valine is nearly identical to another essential amino acid called threonine. Their size and volume are roughly the same but very slightly different in structure. Meat, eggs, and other poultry and dairy products, including soy plants, are rich in valine. An excessive amount of valine may cause hallucination and a skin-crawling sensation. It can affect the functioning of kidneys and liver and increase the concentration of toxic ammonia in the body.

Threonine

Threonine is one of the two proteinogenic amino acids with stereogenic centers, the other one being isoleucine. It is necessary to create glycine and serine and to build collagen, elastin, and muscle tissue. It is the principal part of structural proteins, such as elastin and collagen. Both are important components of connective tissues.

The physiological role of threonine metabolism is potentially ATP production and pH regulation. Threonine is used to treat various nervous disorders like spinal spasticity, multiple sclerosis, etc. It is a precursor to serine and glycine. Glycine reduces constant and unwanted muscle contraction. 

It also plays a role in fat metabolism and the immune system. There are some speculations that predict that threonine affects lung functioning in patients suffering from amyotrophic lateral sclerosis, also called Lou Gehrig's disease. An adult human requires around 20mg/kg of threonine a day.

Threonine plays an important role in supporting digestive health. It forms a mucus gel layer and serves as a barrier to prevent the damage of digestive enzymes. It is essential for healthy gut function, and most of the threonine consumed is absorbed in intestinal-mucosal protein synthesis. Food high in threonine is cottage cheese, poultry, lentils, carrot, banana, sesame, and black turtle bean.

Our body needs enough threonine to support proper immune function. Threonine kinases control epigenetic, transcriptional, and metabolic programs that determine T-cell function. They trigger antigen and cytokine receptors that make up the immune system. Apart from all this, threonine is helpful in improving muscle contractions, supports muscle-bone strength, helps prevent fatty liver, and alleviates anxiety and mild depression. It also accelerates wound healing.

Tryptophan 

Want to have a night of better sleep and fewer headaches? Tryptophan is the key to it all. It is a natural mood regulator that has the ability to help the body produce and balance certain hormones naturally. Tryptophan-rich food or supplements brings a natural calming effect, help with your sleep, fight anxiety, and burn excess body fat.

Tryptophan is often associated with drowsiness and is the precursor to serotonin. Serotonin is a neurotransmitter that has a major role in your appetite, sleep, and mood. An important byproduct of tryptophan is 5HTP (5-hydroxytryptophan), which works in the brain and central nervous system to boost feelings of well-being, connection, and safety. Apart from serotonin, tryptophan is also broken down into melatonin, a hormone associated with the body's sleep-wake cycle. The liver may use tryptophan to produce niacin which is needed for energy metabolism and DNA production.

Milk, turkey, soybeans, sunflower seeds, pumpkin seeds, peanuts, and egg white are the best source of tryptophan. The other essential use of this amino acid is growth in infants and nitrogen balance in adults. Supplements of tryptophan may cause heartburn, stomach pain, bleching, or diarrhoea. The recommended intake for the amino acid is 4mg/kg for a normal adult.

Tryptophan improves sleep quality, lifts your mood, reduces depression and anxiety, helps with recovery from addiction, and reduces headaches and migraine. 5HTP, which is synthesized from tryptophan, has been used to help treat numerous disorders, including sleep disorders, mood disorders, headaches, binge eating, learning disabilities, PMS and menopausal symptoms, fibromyalgia, and more.

Leucine

Leucine is a branched-chain amino acid vital for protein synthesis and growth of muscle and muscle repairing. It helps manage blood sugar levels and improve insulin response by facilitating glucose uptake and the production of growth hormones. Leucine is broken down and absorbed more rapidly than other branched-chain amino acids. It is converted into acetyl-CoA, making it the most important ketogenic amino acid. It is one of the few which is converted into acetyl-CoA as others are converted into glucose.

L-leucine is a popular supplement among athletes and bodybuilders because of its powerful effects on muscle gaining. Leucine produces better results if it is consumed with other amino acids. Leucine supplementation enhances endurance and upper-body power and improves functional performance in older adults. It also aids in fat loss by decreasing fat accumulation during ageing and preventing the development of diet-related obesity. Other benefits of leucine are enhanced fat loss, improved muscle recovery, and decreased muscle loss. 

Leucine metabolism occurs in many tissues in the human body; however, most dietary leucine is metabolized within the liver, adipose tissue, and muscle tissue; adipose and muscle tissue use leucine in the formation of sterols and other compounds. Combined leucine use in these two tissues is seven times greater than in the liver. 

Leucine has a prominent role in muscle recovery in cases of cramps and sore muscles. Consuming leucine right after working out helps stimulate muscle recovery and muscle protein synthesis. There is a lot of different food rich in leucine. Some of them are canned navy beans, cottage cheese, sesame seeds, pumpkin seeds, eggs, hemp seeds, lentils, and spirulina. Its deficiency is rare. 

The ideal intake for leucine is 39-42 mg/kg. Excessive intake side effects associated with leucine are chronic fatigue, toxicity, and impaired coordination. As seen in decompensated maple syrup urine disease, Leucine toxicity causes delirium and neurologic compromise and can be life-threatening. Leucine at a dose exceeding 500 mg/kg/d was observed with hyperammonemia. 

Isoleucine 

It is the third and last branched-chain amino acid. It provides help in muscle metabolism and is heavily concentrated in muscle tissue. Its also important for immune function, haemoglobin production, and energy regulation. Like other branched-chain amino acids, isoleucine plays a very important role in muscle growth and the construction of protein in muscle. It is mainly concentrated in the muscle tissue.

Isoleucine helps lower glucose levels in diabetic person and stimulate insulin-independent glucose uptake in muscle cells. Being branched-chain, many of its uses and functions align with that of leucine and valine. Isoleucine can improve the immune system, including immune organs, cells, and reactive substances. Isoleucine administration can restore the effect of some pathogens on humans and animals' health by increasing the expression of β-defensins.

Like other branched-chain amino acids, Isoleucine is associated with insulin resistance: higher levels of isoleucine are observed in the blood of diabetic mice, rats, and humans. In humans, a protein-restricted diet lowers blood levels of isoleucine and decreases fasting blood glucose levels. In humans, higher dietary levels of isoleucine are associated with greater body mass index. It reduces fatigue and increases body performance. The ideal intake of isoleucine is 20mg/kg. Food sources high in isoleucine are eggs, meat, chard, lentils, pinto beans, watercress, grass-fed beef, brown rice, cashews, Brazil nuts, etc.

Methionine

Methionine has an important role in the health of the human body. It plays an important role in metabolism and detoxification. Methionine is an antioxidant. It may help protect the body from damage caused by ionizing radiation. It may detoxify harmful substances in the body, such as heavy metals. It may also prevent liver damage from acetaminophen poisoning.

As the precursor of other amino acids such as cysteine and taurine, versatile compounds such as SAM-e, and the important antioxidant glutathione, methionine plays a critical role in the metabolism and health of many species, including humans. Methionine may help reduce the risk of colorectal cancer. It is cancer that starts in the colon or rectum. Methionine, along with B vitamins and other minerals, helps reduce this cancer Methionine is also an important part of angiogenesis, the growth of new blood vessels.

Methionine can lower tremors in Parkinson's patients. Patients show improvement in akinesia and rigidity when fed with methionine over a certain period of time. It's also necessary for tissue growth and the absorption of zinc and selenium, minerals that are vital to your health. Loss of methionine has been linked to senile greying of hair.

Methionine is an intermediate in the biosynthesis of cysteine, carnitine, taurine, lecithin, phosphatidylcholine, and other phospholipids. Improper conversion of methionine can lead to atherosclerosis due to the accumulation of homocysteine. Atherosclerosis is a disease in which the wall of the artery develops abnormalities called lesions. These lesions may lead to narrowing due to the buildup of atheromatous plaque. Methionine builds bone strength, increasing athletic performance. Methionine combined with endurance exercise caused lower whole bone mass, size, and strength, but it enhanced natural bone strength overall. Some research shows that methionine may help make some drugs less effective and addictive and support in case of liver disease.

Food rich in methionine are eggs, cheese, oat, peanuts, chickpea, milk, meat, etc. The ideal intake of methionine is 10.4 mg/kg body weight.

We get the required amount of these essential amino acids from food, but doctors recommend the use of supplements in the case of athletes for better performance and enhanced muscle power. But before taking any kind of supplement, it is necessary to consult a healthcare professional. 

From the above discussion, we can point out some common benefits we get from all types of essential amino acids. These are:

  • They help with our mood
  • Improve wound healing and muscle power
  • Build bone strength
  • Biosynthesise protein

Summary

Amino acids are building blocks of the body. They are of three types, essential, non-essential, and conditionally essential. In this article, we talked about the essential amino acids, which are nine in number. They are Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan, and Valine. All of them have various functions and perform different roles in the human body. From increasing bone strength and mass to improving our mood and helping with the functioning of the immune system, they play many roles in our body. Our body does not produce them, so it is necessary for us to make sure that we get the proper amount of these amino acids from our food. The most common food sources for getting all of the above essential amino acids are eggs, meat, poultry products, milk, and soy products like tofu, etc. People often need more of these amino acids than what they get from a balanced diet. In these cases, they take protein supplements to fulfill that requirement. Supplements are common among athletes and bodybuilders. Excessive supplements carry with them many side effects and can lead to some serious problems. Hence it is necessary to always consult a professional healthcare expert before going on with any supplements.

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