Amino acids are the building blocks of proteins and intermediaries in metabolism. Within the proteins in the human body, there are 20 amino acids essential for life. They are classified into essential, non-essential, and conditionally essential categories. There are 8 essential amino acids, which means they must be obtained through diet, and 2 are conditionally essential (arginine and histidine). The remaining 10 amino acids can be synthesized by the body itself (non-essential amino acids). Amino acids are the building blocks of proteins and intermediaries in metabolism. Within the proteins in the human body, there are 20 amino acids essential for life. They are classified into essential, non-essential, and conditionally essential categories. There are 8 essential amino acids, which means they must be obtained through diet, and 2 are conditionally essential (arginine and histidine). The remaining 10 amino acids can be synthesized by the body itself (non-essential amino acids). Unlike fats or starches, the human body cannot store amino acids for later use, so the diet must daily provide all the necessary amino acids. The ten amino acids that the body can produce on its own (non-essential) are alanine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, proline, serine, and tyrosine. Essential amino acids, which must be obtained from food, include isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. 
The amino acid alanine helps the body convert simple sugar glucose into energy and assists in the elimination of toxins from the liver. Alanine protects cells from damage during intense aerobic activity when the body starts using muscle proteins to produce energy. Additionally, alanine is crucial for maintaining balanced levels of nitrogen and glucose in the body through a series of chemical reactions known as the alanine cycle. During this cycle, excess amino acids in cells and tissues are transferred to a transport molecule called pyruvate, which is created by breaking down glucose molecules.
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Alanine plays a key role in maintaining glucose levels, and thereby energy supply in the body. For example, chronic fatigue syndrome is associated with high levels of alanine and low levels of tyrosine and phenylalanine. Furthermore, alanine helps regulate blood sugar levels. Studies have confirmed that people with diabetes who are undergoing insulin therapy successfully prevent nocturnal hypoglycemia by taking alanine, a common issue among those with diabetes.
Alanine is a non-essential amino acid, but under certain conditions where the body cannot synthesize it, it becomes essential and needs to be obtained through the diet. This occurs in cases of dietary disorders, liver disease, diabetes, and various genetic disorders. Low levels of alanine are also observed in individuals with hypoglycemia, diabetes, and hepatitis. Alanine is also necessary for the absorption of vitamins B5 and B6. Good sources of alanine include poultry meat, eggs, dairy products, and fish, as well as protein-rich plants like avocados. Additionally, alanine can also be purchased as a dietary supplement.
Arginine is an essential amino acid involved in maintaining the health and proper functioning of the liver, skin, joints, and muscle tissue. It helps strengthen the immune system, regulate hormones and blood sugar levels, and also affects male fertility. Arginine is considered a semi-essential amino acid because the body can synthesize it, but under certain conditions such as specific dietary regimes or illnesses, additional supplementation is needed. For newborns, arginine is considered an essential amino acid as they cannot synthesize it in the first months of life and must obtain it from their diet.
Arginine supports immune system health by increasing the production of T-lymphocytes (T-cells). Recent studies have shown the potential of arginine in treating AIDS, cancer, and other diseases related to a weakened immune system. Additionally, arginine helps detoxify the liver by neutralizing the effects of ammonia and other negative substances in the body. It is necessary for the production of urea, which helps eliminate ammonia from the body. Arginine is found in higher concentrations in the skin and plays an important role in the health of muscles, joints, and connective tissue. It aids the body in utilizing creatine and nitrogen, which help in building muscle mass and are involved in muscle metabolism. Studies link arginine to reduced body fat and increased production of growth hormone.
This type of amino acid can be found in chocolate, carob, coconut, dairy products, gelatin, meat, oats, peanuts, nuts, and yeast. For those with immune system issues, fighting infections, undergoing dialysis, or with liver problems, arginine supplementation is recommended. A typical dose is 2-3 grams of arginine per day. 
Asparagine, or aspartic acid, is an amino acid involved in the proper functioning of brain cells and the synthesis of ammonia. It also participates in protein synthesis. Low levels of asparagine are associated with poor metabolism and improper synthesis of aspartic acid, which can result in the inability to properly synthesize and excrete urea, the main waste product of excess dietary protein. This can lead to increased levels of toxic nitrogen-containing metabolites in the body, causing headaches, depression, irritability, and in extreme cases, psychosis. Asparagine is found in animal-derived foods, such as meat, eggs, and dairy products.
Aspartic acid, also known as L-aspartate, helps to strengthen and accelerate metabolism and is used in the treatment of fatigue and depression. Aspartic acid plays a crucial role in many metabolic cycles in the body, such as the Krebs cycle, during which amino acids and biochemicals, including asparagine, arginine, lysine, methionine, and others, are synthesized. 
Due to its role in cellular energy production, aspartic acid is associated with treating chronic fatigue, and studies confirm its impact on increasing endurance and strength. It also aids in transporting minerals into cells, strengthens the immune system by promoting the production of immunoglobulins and antibodies, improves concentration, and helps in eliminating toxins from cells, especially ammonia. As an non-essential amino acid, the body can produce aspartic acid on its own, but supplementation is recommended for individuals with eating disorders or those on restrictive diets. It can be found in dairy products, beef, poultry, and is also available as a dietary supplement, commonly used to boost energy.
Cysteine is a non-essential amino acid that is found in the form of N-acetyl cysteine, an amino acid used in the production of glutathione, a natural antioxidant produced in the body to combat free radicals. Without glutathione, the immune system would be severely compromised and unable to fight toxins and diseases. Cysteine is present in beta-keratin, a crucial protein found in the skin, hair, and nails. It helps maintain skin health, support collagen production, and preserve skin elasticity. Cysteine is associated with combating cancer, heavy metal poisoning, bronchitis, heart disease, and cystic fibrosis. Due to its detoxifying effects, it enhances the benefits of exercise by protecting the body from oxidative stress. Cysteine is found in protein-rich foods such as meat and eggs. Wheat flour, broccoli, garlic, onions, and red peppers are also good sources of cysteine.
Phenylalanine is an essential amino acid needed for the normal functioning of the central nervous system. It is used in controlling symptoms of depression and chronic pain, as well as in treating other disorders related to poor central nervous system function. The body needs phenylalanine to produce epinephrine (adrenaline), dopamine, and norepinephrine (noradrenaline), three neurotransmitters that regulate our perception and interaction with the environment. Phenylalanine is recommended for individuals suffering from Parkinson’s disease, schizophrenia, as well as those with arthritis, obesity, and mild forms of depression. It is not recommended for individuals with high blood pressure. Phenylalanine should be taken under medical supervision. 
Glutamic acid, also known as glutamate, is an excitatory neurotransmitter that increases the release of neurons in the central nervous system. It plays a crucial role in sugar and fat metabolism and contributes to the transport of potassium into the spinal fluid and the brain. The brain uses this amino acid as fuel for proper function. It is used in the treatment of epilepsy, various forms of mental retardation, muscular dystrophy, ulcers, and hypoglycemic coma. It is also a component of folic acid, a B-complex vitamin that helps the body break down amino acids.
Glutamine is an amino acid that assists in the building and preservation of muscle tissue. It also aids in the removal of ammonia from the liver and helps maintain the health of the central nervous system. When it reaches the brain, glutamine is converted into glutamic acid, which supports proper brain function. Glutamine is used in the treatment of epilepsy, depression, schizophrenia, and senility. This amino acid is also an important energy source for the central nervous system. Additionally, glutamine plays a role in maintaining digestive health and pH balance. It helps in transporting nitrogen to the muscles, preventing muscle catabolism, and preserving muscle tissue. It is also effective in recovery after surgical procedures and stress. Glutamine is found in many foods but is destroyed by thermal processing. Good sources include raw spinach and parsley. In addition to food, it is available as a dietary supplement in the form of tablets and powder.
Glycine is a non-essential amino acid that plays a role in the formation of muscle tissue and the conversion of glucose into energy. It is also crucial for maintaining the health of the central nervous system and digestive tract, and through its antioxidant properties, it helps protect against some forms of cancer. By increasing creatine levels in the body, glycine contributes to the protection of muscle tissue, and high levels of glycine are also found in the skin and connective tissues. Glycine regulates blood sugar levels, making it useful in treating symptoms associated with fatigue, anemia, and chronic fatigue syndrome. Glycine is found in protein-rich foods such as fish, meat, legumes, milk, and cheeses. In addition to dietary sources, glycine can also be taken as a dietary supplement in the form of capsules or powder.
Histidine is a conditionally essential amino acid involved in the development and maintenance of virtually all parts of the body, particularly in the myelin sheath that surrounds nerve cells, ensuring the transmission of messages from the brain to other parts of the body. 
It is used in the treatment of certain mental disorders and various sexual dysfunctions. Additionally, this amino acid protects against radiation damage and helps in the elimination of heavy metals from the body. Histidine can be found in protein-rich foods such as meat, dairy products, and grains.
Isoleucine is an essential amino acid with its strongest effects related to increasing endurance and aiding in the maintenance and repair of muscle tissue after intense physical activities and injuries. Isoleucine is one of the three branched-chain amino acids (BCAAs) along with valine and leucine, which speed up recovery after exercise. Isoleucine helps in maintaining stable energy levels by regulating blood sugar levels. Isoleucine can be found in nuts, meat, seeds, eggs, fish, lentils, peas, and soy. It is recommended to take isoleucine in combination with the other two BCAAs.
Leucine is a branched-chain amino acid (BCAA) that plays a role in the repair and preservation of muscle tissue, regulating blood sugar levels, and providing energy to the body. Leucine supports the production of growth hormones, helps in burning visceral fat (which is located deeper in the body and is the last to respond to diet and exercise). Among the BCAAs, leucine is the most effective in preventing the breakdown and loss of muscle tissue because it is broken down and converted to glucose much faster than valine and isoleucine. Leucine also promotes the health of bones, skin, and muscle tissues after injuries and surgical procedures. Natural sources of leucine include brown rice, meat, nuts, legumes, soy flour, and whole grain flour.
Lysine is an essential amino acid known for its antiviral properties. It helps in preventing outbreaks of herpes and colds and is necessary for hormone production as well as the growth and maintenance of bone health, both in children and adults. 
Lysine can be found in cheeses, eggs, fish, certain types of beans, milk, potatoes, red meat, soy, and yeast. As a dietary supplement, it is available in capsule or liquid form. Lysine is usually taken under medical supervision, often in combination with other medications, for the treatment of herpes.
Methionine is an essential amino acid that aids the body in utilizing and eliminating fats. It contains sulfur, which is necessary for the production of the body’s least abundant natural antioxidant – glutathione. Methionine also supports the production of two other sulfur-containing amino acids: cysteine and taurine, which are involved in detoxification, building stronger connective tissues, and maintaining cardiovascular health. Methionine assists the liver in digesting fats and is necessary for the production of creatine, which generates energy in muscles. Creatine is associated with improved performance in short-duration, high-intensity exercises. Methionine is essential for collagen production, which is involved in building skin, nails, and connective tissues. Methionine can be found in legumes, eggs, fish, garlic, lentils, meat, onions, seeds, and yogurt. As a dietary supplement, it is available in capsule and powder forms.
Proline is a non-essential amino acid needed for the production of collagen and cartilage. It helps maintain the flexibility of muscles and joints and reduces the formation of wrinkles and spots due to UV radiation. Proline also supports the quality and health of muscle tissue, and decreased levels of this amino acid are observed in long-distance runners. The body produces proline from glutamic acid, and its deficiency is very rare. It can occur in individuals recovering from burns or other skin injuries. In combination with vitamin C, proline is recommended for maintaining cardiovascular health. The best sources of proline are meat, eggs, and dairy products. People on low-protein diets or vegetarians may consider taking dietary supplements that include proline.
Serine is a non-essential amino acid derived from the amino acid glycine. It plays a role in maintaining overall health, both physical and mental. Serine is particularly important for the proper functioning of the brain and central nervous system. Serine is involved in DNA and RNA function, fat and fatty acid metabolism, muscle formation, and maintaining immune system health. Proteins that make up the brain and form the protective myelin sheath surrounding nerves contain serine. Serine also participates in the production of tryptophan, an amino acid involved in the synthesis of serotonin, a chemical that affects mood. Adequate amounts of vitamin B3, B6, and folic acid are necessary for the proper functioning of serine. Serine can be found in dairy products, peanuts, wheat gluten, and soy.
Threonine is an essential amino acid that ensures normal growth by participating in the maintenance of proper protein balance in the body. Threonine supports cardiovascular health, as well as the proper functioning of the liver, immune system, and central nervous system. Threonine is needed for the production of glycine and serine, amino acids essential for the synthesis of collagen, elastin, and muscle tissue. It plays a role in building strong bones and dental enamel and also accelerates the healing of injuries. Threonine is found in meat, dairy products, grains, mushrooms, and green leafy vegetables. Supplementation with threonine is recommended for vegetarians and vegans. 
Tryptophan is an essential amino acid necessary for normal growth and development in children and for nitrogen balance in adults. The body uses tryptophan to produce niacin and serotonin, the latter of which influences healthy sleep and mood. For tryptophan to be converted into niacin, the body needs adequate amounts of iron, riboflavin, and vitamin B6. Good sources of tryptophan include cheeses, chicken, eggs, fish, milk, nuts, peanut butter, peanuts, pumpkin seeds, sesame seeds, soy, tofu, and turkey.
Tyrosine is a non-essential amino acid that helps regulate mood and stimulates the nervous system. It can accelerate metabolism and alleviate conditions such as chronic fatigue. The body needs tyrosine to produce brain chemicals that regulate appetite, pain sensitivity, and the body’s stress response. 
Additionally, tyrosine is involved in the normal functioning of the pituitary gland, adrenal glands, and thyroid gland. Tyrosine, along with phenylalanine, is required for the production of neurotransmitters in the brain. A deficiency in either of these amino acids can lead to depression, anxiety, reduced libido, and chronic fatigue. Tyrosine can be found in almonds, avocados, bananas, dairy products, and seeds. It is also available as a dietary supplement in the form of powder and capsules.
Valine is the third among the branched-chain amino acids (BCAA) that supports normal growth, tissue recovery, regulates blood sugar levels, and provides energy to the body. Valine helps with the functioning of the central nervous system and is necessary for proper mental function.
Valine prevents muscle catabolism by supplying muscles with additional glucose for energy production during intense physical activity. This amino acid assists in eliminating toxic nitrogenous waste from the liver and aids in the treatment of liver and pancreas diseases.
Natural sources of valine include meat, dairy products, mushrooms, peanuts, and soy. Valine is recommended to be taken as a dietary supplement in the form of BCAA. Text taken from Fitness.com http://www.fitness.com.hr/prehrana/dodaci-prehrani/Abeceda-aminokiselina.aspxAutor Zorana Jagodić
