THE FUNCTION OF AMINO ACIDS


Amino acids are the chemical units or "building blocks," as they are popularly called, that make up proteins. Amino acids contain about 16 percent nitrogen. Chemically, this is what distinguishes them from the other two basic nutrients, sugars and fatty acids, which do not contain nitrogen. To understand how vital amino acids are, you must understand how essential proteins are to life. It is protein that provides the structure for all living things. Every living organism, from the largest animal to the tiniest microbe, is composed of protein. And in its various forms, protein participates in the vital chemical processes that sustain life.

Proteins are a necessary part of every living cell in the body. Next to water, protein makes up the greatest portion of our body weight. In the human body, protein substances make up the muscles, ligaments, tendons, organs, glands, nails, hair, and many vital body fluids, and are essential for the growth of bones. The enzymes and hormones that catalyze and regulate all bodily processes are proteins. Proteins help to regulate the body's water balance and maintain the proper internal pH. They assist in the exchange of nutrients between the intercellular fluids and the tissues, blood, and lymph. A deficiency of protein can upset the body's fluid balance, causing oedema. Proteins form the structural basis of chromosomes, through which genetic information is passed from parents to offspring. The genetic "code" contained in each cell's DNA is actually information for how to make that cell's proteins.

Proteins are chains of amino acids linked together by what are called peptide bonds. Each individual type of protein is composed of a specific group of amino acids in a specific chemical arrangement. It is the particular amino acids present and the way in which they are linked together in sequence that gives the proteins that make up the various tissues their unique functions and characters. Each protein in the body is tailored for a specific need; proteins are not interchangeable.
The proteins that make up the human body are not obtained directly from the diet. Rather, dietary protein is broken down into its constituent amino acids, which the body then uses to build the specific proteins it needs. Thus, it is the amino acids rather than protein that are the essential nutrients.

In addition to combining to form the body's proteins, some amino acids act as neurotransmitters or as precursors of neurotransmitters, the chemicals that carry information from one nerve cell to another. Certain amino acids are thus necessary for the brain to receive and send messages. Unlike many other substances, neurotransmitters are able to pass through the blood-brain barrier. This is a kind of defensive shield designed to protect the brain from toxins and foreign invaders that may be circulating in the bloodstream. The endothelial cells that make up the walls of the capillaries in the brain are much more tightly meshed together than are those of capillaries elsewhere in the body. This prevents many substances, especially water-based substances, from diffusing through the capillary walls into brain tissue. Because certain amino acids can pass through this barrier, they can be used by the brain to communicate with nerve cells elsewhere in the body.

Amino acids also enable vitamins and minerals to perform their jobs properly. Even if vitamins and minerals are absorbed and assimilated by the body, they cannot be effective unless the necessary amino acids are present. For example, low levels of the amino acid tyrosine may lead to iron deficiency. Deficiency and/or impaired metabolism of the amino acids methionine and taurine have been linked to allergies and autoimmune disorders. Many elderly people suffer from depression or neurological problems that may be associated with deficiencies of the amino acids tyrosine, tryptophan, phenylalanine, and histidine, and also of the branched-chain amino acids—valine, isoleucine, and leucine. These are amino acids that can be used to provide energy directly to muscle tissue. High doses of branched-chain amino acids have been used in hospitals to treat people suffering from trauma and infection.

There are approximately twenty-eight commonly known amino acids that are combined in various ways to create the hundreds of different types of proteins present in all living things. In the human body, the liver produces about 80 percent of the amino acids needed. The remaining 20 percent must be obtained from the diet. These are called the essential amino acids. The essential amino acids that must enter the body through diet are histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. The nonessential amino acids, which can be manufactured in the body from other amino acids obtained from dietary sources, include alanine, arginine, asparagine, aspartic acid, citrulline, cysteine, cystine, gamma-aminobutyric acid, glutamic acid, glutamine, glycine, ornithine, proline, serine, taurine, and tyrosine.

The fact that they are termed "nonessential" does not mean that they are not necessary, only that they need not be obtained through the diet because the body can manufacture them as needed.
The processes of assembling amino acids to make proteins, and of breaking down proteins into individual amino acids for the body's use, are continuous ones. When we need more enzyme proteins, the body produces more enzyme proteins; when we need more cells, the body produces more proteins for cells. These different types of proteins are produced as the need arises. Should the body become depleted of its reserves of any of the essential amino acids, it would not be able to produce the proteins that require those amino acids. If even one essential amino acid is missing, the body cannot continue proper protein synthesis. This can lead to lack of vital proteins in the body, which can cause problems ranging from indigestion to depression to stunted growth.

How could such a situation occur? More easily than you might think. Many factors can contribute to deficiencies of essential amino acids, even if you eat a well-balanced diet that contains enough protein. Impaired absorption, infection, trauma, stress, drug use, age, and imbalances of other nutrients can all affect the availability of essential amino acids in the body. If your diet is not properly balanced—that is, if it fails to supply adequate amounts of the essential amino acids—sooner or later, this will become apparent as some type of physical disorder.

This does not mean, however, that eating a diet containing enormous amounts of protein is the answer. In fact, it is unhealthy. Excess protein puts undue stress on the kidneys and the liver, which are faced with processing the waste products of protein metabolism. Nearly half of the amino acids in dietary protein are transformed into glucose by the liver and utilized to provide needed energy to the cells. This process results in a waste product, ammonia. Ammonia is toxic to the body, so the body protects itself by having the liver turn the ammonia into the much less toxic compound urea, which is then carried through the bloodstream, filtered out by the kidneys, and excreted.

As long as protein intake is not too great and the liver is working properly, ammonia is neutralized almost as soon as it is produced, so it does no harm. However, if there is too much ammonia for the liver to cope with—as a result of too much protein consumption, poor digestion, and/or a defect in liver function—toxic levels may accumulate. Strenuous exercise also tends to promote the accumulation of excess ammonia. This may put a person at risk for serious health problems, including encephalopathy (brain disease) or hepatic coma. Abnormally high levels of urea can also cause problems, including inflamed kidneys and back pain. Therefore, it is not the quantity but the quality of protein in the diet that is important.
It is possible to take supplements containing amino acids, both essential and nonessential. For certain disorders, taking supplements of specific amino acids can be very beneficial. When you take a specific amino acid or amino acid combination, it supports the metabolic pathway involved in your particular illness. Vegetarians, especially vegans, would be wise to take a formula containing all of the essential amino acids to ensure that their protein requirements are met.


WHAT'S ON THE SHELVES


Supplemental amino acids are available in combination with various multivitamin formulas, as protein mixtures, in a wide variety of food supplements, and in a number of amino acid formulas. They can be purchased as capsules, tablets, liquids, and powders. Most amino acid supplements are derived from animal protein, yeast protein, or vegetable protein. Crystalline free-form amino acids are generally extracted from a variety of grain products. Brown rice bran is a prime source, although cold-pressed yeast and milk proteins are also used.

Most of the amino acids (except for glycine) can appear in two forms, the chemical structure of one being the mirror image of the other. These are called the D- and L- forms—for example, D-cystine and L-cystine. The "D" stands for dextro (Latin for "right") and the "L" for leva (Latin for "left"); these terms denote the direction of the rotation of the spiral that is the chemical structure of the molecule. Proteins in animal and plant tissue are made from the L- forms of amino acids (with the exception of phenylalanine, which is also used in the form of DL-phenylalanine, a mixture of the D- and L- forms). Thus, with respect to supplements of amino acids, products containing the L- forms of amino acids are considered to be more compatible with human biochemistry.

Free-form means the amino acid is in its purest form. Free-form amino acids need no digestion and are absorbed directly into the bloodstream. These white crystalline amino acids are stable at room temperature and decompose when heated to temperatures of 350°F to 660°F (180°C to 350°C). They are rapidly absorbed and do not come from potentially allergenic food sources. For best results, choose encapsulated powders or powder.

Each amino acid has specific functions in the body. The many functions and possible symptoms of deficiency of twenty-eight amino acids and related compounds are described below. When taking amino acids individually for healing purposes, take them on an empty stomach to avoid making them compete for absorption with the amino acids present in foods. When taking individual amino acids, it is best to take them in the morning or between meals, with small amounts of vitamin B and vitamin C to enhance absorption. When taking an amino acid complex that includes all of the essential amino acids, it is best to take it one-half hour away from a meal, either before or after. If you are taking individual amino acids, it is wise also to take a full amino acid complex, including both essential and nonessential amino acids, at a different time. This is the best way to assure you have adequate amounts of all the necessary amino acids.

Individual amino acids should not be taken for long periods of time. A good rule to follow is to alternate the individual amino acids that fit your needs and back them up with an amino acid complex, taking the supplements for two months and then discontinuing them for two months. Researchers warn against taking large doses of amino acids for extended periods of time. Moderation is the key. Some amino acids have potentially toxic effects when taken in high doses (over 6,000 milligrams per day) and may cause neurological damage. These include aspartic acid, glutamic acid, homocysteine, serine, and tryptophan. Cysteine can be toxic if taken in amounts over 1,000 milligrams per day. Do not give supplemental amino acids to a child or take doses of any amino acid in excess of the amount recommended unless specifically directed to do so by your health care provider.


THE ABC'S OF AMINO ACIDS

Alanine
Alanine aids in the metabolism of glucose, a simple carbohydrate that the body uses for energy. Epstein-Barr virus and chronic fatigue have been associated with excessive alanine levels and low levels of tyrosine and phenylalanine. One form of alanine, beta-alanine, is a constituent of pantothenic acid (vitamin 65) and coenzyme A, a vital catalyst in the body.

Arginine
Arginine retards the growth of tumours and cancer by enhancing immune function. It increases the size and activity of the thymus gland, which manufactures T lymphocytes (T cells), crucial components of the immune system. Arginine may therefore benefit those suffering from AIDS and malignant diseases that suppress the immune system. It is also good for liver disorders such as cirrhosis of the liver and fatty liver; it aids in liver detoxification by neutralizing ammonia. Seminal fluid contains arginine. Studies suggest that sexual maturity may be delayed by arginine deficiency; conversely, arginine is useful in treating sterility in men. It is found in high concentrations in the skin and connective tissues, making it helpful for healing and repair of damaged tissue.

Arginine is important for muscle metabolism. It helps to maintain a proper nitrogen balance byactingasa vehicle for transportation and storage, and aiding in the excretion, of excess nitrogen. This amino acid aids in weight loss because it facilitates an increase in muscle mass and a reduction of body fat. It is also involved in a variety of enzymes and hormones. It aids in stimulating the pancreas to release insulin, is a component of the pituitary hormone vasopressin, and assists in the release of growth hormones. Because arginine is a component of collagen and aids in building new bone and tendon cells, it can be good for arthritis and connective tissue disorders. Scar tissue that forms during wound healing is made up of collagen, which is rich in arginine. A variety of functions, including insulin production, glucose tolerance, and liver lipid metabolism, are impaired when the body is deficient in arginine.

This amino acid can be produced in the body; however, in newborn infants, production may not occur quickly enough to keep up with requirements. Foods high in arginine include carob, chocolate, coconut, dairy products, gelatin, meat, oats, peanuts, soybeans, walnuts, white flour, wheat, and wheat germ.
Those with viral infections such as herpes should not take supplemental arginine, and should avoid foods rich in arginine, as it appears to promote the growth of certain viruses. L-Arginine supplements should be avoided by pregnant and lactating women. Persons with schizophrenia should avoid amounts over 30 milligrams daily. Long-term use, especially of high doses, is not recommended. One study found that several weeks of large doses may result in thickening and coarsening of the skin.

Asparagine
Asparagine is needed to maintain balance in the central nervous system; it prevents you from being either overly nervous or overly calm. It promotes the process by which one amino acid is transformed into another in the liver. This amino acid is found mostly in meat sources.

Aspartic Acid
Because aspartic acid increases stamina, it is good for fatigue and plays a vital role in metabolism. Chronic fatigue may result from low levels of aspartic acid, because this leads to lowered cellular energy. It is beneficial for neural and brain disorders. It is good for athletes, and helps to protect the liver by aiding in the removal of excess ammonia. Aspartic acid combines with other amino acids to form molecules that absorb toxins and remove them from the bloodstream. It aids cell function and the function of RNA and DNA, which are the carriers of genetic information. It enhances the production of immunoglobulins and antibodies (immune system proteins). Plant protein, especially which found in sprouting seeds, contains an abundance of aspartic acid.

Carnitine
Carnitine is not an amino acid in the strictest sense (it is actually a substance related to the B vitamins). However, because it has a chemical structure similar to that of amino acids, it is usually considered together with them. Unlike true amino acids, carnitine is not used for protein synthesis or as a neurotransmitter. Its main function in the body is to help transport long-chain fatty acids, which are burned within the cells to provide energy. This is a major source of energy for the muscles. Carnitine thus increases the use of fat as an energy source. This prevents fatty build-up, especially in the heart, liver, and skeletal muscles. Carnitine reduces the health risks posed by poor fat metabolism associated with diabetes; inhibits alcohol-induced fatty liver; and lessens the risk of heart disorders. Studies have shown that damage to the heart from cardiac surgery can be reduced by treatment with carnitine. It has the ability to lower blood triglyceride levels, aid in weight loss, and improve muscle strength in people with neuro-muscular disorders. Conversely, it is believed that carnitine deficiency may be a contributor to certain types of muscular dystrophy, and it has been shown that these disorders lead to losses of carnitine in the urine. People with such conditions need greater than normal amounts of carnitine. Carnitine also enhances the effectiveness of the antioxidant vitamins E and C.

Carnitine can be manufactured by the body if sufficient amounts of iron, vitamin BI (thiamine), vitamin B6 (pyri-doxine), and the amino acids lysine and methionine are available. The synthesis of carnitine also depends on the presence of adequate levels of vitamin C. Inadequate intake of any of these nutrients can result in a carnitine deficiency. Carnitine can also be obtained from food, primarily meats and other foods of animal origin.

Many cases of carnitine deficiency have been identified as partly genetic in origin, resulting from an inherited defect in carnitine synthesis. Possible symptoms of deficiency include confusion, heart pain, muscle weakness, and obesity. Because of their generally greater muscle mass, men need more carnitine than women do. Vegetarians are more likely than non-vegetarians to be deficient in carnitine because it is not found in vegetable protein. Moreover, neither methionine nor lysine, two of the key constituents from which the body makes carnitine, is obtainable from vegetable sources in sufficient amounts. To ensure adequate production of carnitine, vegetarians should take supplements or should eat grains, such as cornmeal, that have been fortified with lysine.
Supplemental carnitine is available in different forms, including D-carnitine, L-carnitine, DL-carnitine, and ace-till-L-carnitine. L-carnitine is the preferred form.

Coralline
Coralline promotes energy, stimulates the immune system, is metabolized to form L-argentine, and detoxifies ammonia, which damages living cells. Coralline is found primarily in the liver.

Cytokine and Sistine
These two amino acids are closely related; each molecule of cosine consists of two molecules of cytokine joined together. Cytokine is very unstable and is easily converted to L-cystine; however, each form is capable of converting into the other as needed. Both are sulfur-containing amino acids that aid in the formation of skin and are important in detoxification.
Cysteine is present in alpha-keratin, the chief protein constituent of the fingernails, toenails, skin, and hair. Cysteine aids in the production of collagen and promotes the proper elasticity and texture of the skin. It is also found in a variety of other proteins in the body, including several of the digestive enzymes.

Cysteine helps to detoxify harmful toxins and protect the body from radiation damage. It is one of the best free radical destroyers, and works best when taken with selenium and vitamin E. Cysteine is also precursor to glutathione, a substance that detoxifies the liver by binding with potentially harmful substances there. It helps to protect the liver and brain from damage due to alcohol, drugs, and toxic compounds in cigarette smoke.

Since cysteine is more soluble than cystine, it is used more readily in the body and is usually best for treating most illnesses. This amino acid is formed from L-methion-ine in the body. Vitamin B is necessary for cysteine synthesis, which may not take place as it should in the presence of chronic disease. Therefore, people with chronic illnesses may need higher than normal doses of cysteine, as much as 1,000 milligrams three times daily for a month at a time.

Supplementation with L-cysteine is recommended in the treatment of rheumatoid arthritis, hardening of the arteries, and mutagenic disorders such as cancer. It promotes healing after surgery and severe burns, chelates heavy metals, and binds with soluble iron, aiding in iron absorption. This amino acid also promotes the burning of fat and the building of muscle. Because of its ability to break down mucus in the respiratory tract, L-cysteine is often beneficial in the treatment of bronchitis, emphysema, and tuberculosis. It promotes healing from respiratory disorders and plays an important role in the activity of white blood cells, which fight disease.
Cystine or the N-acetyl form of cysteine (N-acetylcys teine) may be used in place of L-cysteine. N-acetylcysteine aids in preventing side effects from chemotherapy and radiation therapy. Because it increases glutathione levels in the lungs, kidneys, liver, and bone marrow, it has an anti-aging effect on the body—reducing the accumulation of age spots, for example. N-acetylcysteine has been shown to be more effective at boosting glutathione levels than supplements of cystine or even of glutathione itself.
People who have diabetes should be cautious about taking supplemental cysteine because it is capable of inactivating insulin. Persons with cystinuria, a rare genetic condition that leads to the formation of cystine kidney stones, should not take cysteine.

Dimethylglycine (DMG)
Dimethylglycine (DMG) is a derivative of glycine, the simplest of the amino acids. It acts as a building block for many important substances, including the amino acid methionine, choline, a number of important hormones and neurotransmitters, and DNA.
Low levels of DMG are present in meats, seeds, and grains. No deficiency symptoms are associated with a lack of DMG in the diet, but taking supplemental DMG can have a wide range of beneficial effects, including helping the body maintain high energy levels and boosting mental acuity. DMG has been found to enhance the immune system and to reduce elevated blood cholesterol and triglyceride levels. It improves oxygen utilization by the body, helps to normalize blood pressure and blood glucose levels, and improves the functioning of many important organs. It may also be useful for controlling epileptic seizures. Aangamik DMG from FoodScience Laboratories is a good source of supplemental DMG.

Gamma-Amino butyric Acid
Gamma-amino butyric acid (GABA) is an amino acid that acts as a neurotransmitter in the central nervous system. It is essential for brain metabolism, aiding in proper brain function. GABA is formed in the body from another amino acid, glutamic acid. Its function is to decrease neuron activity and inhibit nerve cells from over firing. Together with niacinamide and inositol, it prevents anxiety- and stress-related messages from reaching the motor centres of the brain by occupying their receptor sites.

GABA can be taken to calm the body in much the same way as diazepam (Valium), chlordiazepoxide (Librium), and other tranquilizers, but without the fear of addiction. GABA has been used in the treatment of epilepsy and hypertension. It is good for depressed sex drive because of its ability as a relaxant. It is also useful for enlarged prostate, probably because it plays a role in the mechanism regulating the release of sex hormones. GABA is effective in treating attention deficit disorder.
Too much GABA, however, can cause increased anxiety, shortness of breath, numbness around the mouth, and tingling in the extremities.

Glutamic Acid
Glutamic acid is an excitatory neurotransmitter that increases the firing of neurons in the central nervous system. It is a major excitatory neurotransmitter in the brain and spinal cord and is the precursor of GABA.
This amino acid is important in the metabolism of sugars and fats, and aids in the transportation of potassium across the blood-brain barrier. Although it does not pass the blood-brain barrier as readily as glutamine does, it is found at high levels in the blood and may infiltrate the brain in small amounts. The brain can use glutamic acid as fuel. Glutamic acid can detoxify ammonia by picking up nitrogen atoms, in the process creating another amino acid, glutamine. The conversion of glutamic acid into glutamine is the only means by which ammonia in the brain can be detoxified.
Glutamic acid helps to correct personality disorders and is useful in treating childhood behavioural disorders. It is used in the treatment of epilepsy, mental retardation, muscular dystrophy, ulcers, and hypoglycemic coma, a complication of insulin treatment for diabetes.

Glutamine
Glutamine is the most abundant free amino acid found in the muscles of the body. Because it can readily pass the blood-brain barrier, it is known as brain fuel. In the brain, glutamine is converted into glutamic acid—which is essential for cerebral function—and vice versa. It also increases the amount of GABA, which is needed to sustain proper brain function and mental activity. It assists in maintaining the proper acid/alkaline balance in the body, and is the basis of the building blocks for the synthesis of RNA and DNA. It promotes mental ability and the maintenance of a healthy digestive tract.


When an amino acid is broken down, nitrogen is released. The body needs nitrogen, but free nitrogen can form ammonia, which is especially toxic to brain tissues. The liver can convert nitrogen into urea, which is excreted in the urine, or nitrogen may attach itself to glutamic acid. This process forms glutamine. Glutamine is unique among the amino acids in that each molecule contains not one nitrogen atom but two. Thus, its creation helps to clear ammonia from the tissues, especially brain tissue, and it can transfer nitrogen from one place to another.


Glutamine is found in large amounts in the muscles and is readily available when needed for the synthesis of skeletal muscle proteins. Because this amino acid helps to build and maintain muscle, supplemental glutamine is useful for dieters and bodybuilders. More importantly, it helps to prevent the kind of muscle-wasting that can accompany prolonged bed rest or diseases such as cancer and AIDS. This is because stress and injury (including surgical trauma) cause the muscles to release glutamine into the bloodstream. In fact, during times of stress, as much as one third of the glutamine present in the muscles maybe released. As a result, stress and/or illness can lead to the loss of skeletal muscle. If enough glutamine is available, however, this can be prevented.


Supplemental L-glutamine can be helpful in the treatment of arthritis, autoimmune diseases, fibrosis, intestinal disorders, and peptic ulcers, connective tissue diseases such as polymyositis and scleroderma, and tissue damage due to radiation treatment for cancer. L-glutamine can enhance mental functioning, and has been used to treat a range of problems including developmental disabilities, epilepsy, fatigue, impotence, schizophrenia, and senility. L-glutamine decreases sugar cravings and the desire for alcohol, and is useful for recovering alcoholics.


Many plant and animal substances contain glutamine, but it is easily destroyed by cooking. If eaten raw, spinach and parsley are good sources. Supplemental glutamine must be kept absolutely dry or the powder will degrade into ammonia and pyroglutamic acid. Glutamine should not be taken by persons with cirrhosis of the liver, kidney problems, Reye's syndrome, or any type of disorder that can result in an accumulation of ammonia in the blood. For such individuals, taking supplemental glutamine may only cause further damage to the body. Be aware that although the names sound similar, glutamine, glutamic acid (also sometimes called glutamate); glutathione, gluten, and monosodium glutamate are all different substances.

Glutathione
Like carnitine, glutathione is not technically one of the amino acids. It is a compound classified as a tripeptide, and the body produces it from the amino acids cysteine, glutamic acid, and glycine. Because of its close relationship to these amino acids, however, it is usually considered together with them.


Glutathione is a powerful antioxidant that is produced in the liver. The largest stores of glutathione are found in the liver, where it detoxifies harmful compounds so that they can be excreted through the bile. Some glutathione is released from the liver directly into the bloodstream, where it helps to maintain the integrity of red blood cells and protect white blood cells. Glutathione is also found in the lungs and the intestinal tract. It is needed for carbohydrate metabolism, and also appears to exert anti-aging effects, aiding in the breakdown of oxidized fats that may contribute to atherosclerosis.


A deficiency of glutathione first affects the nervous system, causing such symptoms as lack of coordination, mental disorders, tremors, and difficulty maintaining balance. These problems are believed to be due to the development of lesions in the brain.
As we age, glutathione levels decline, although it is not known whether this is because we use it more rapidly or produce less of it to begin with. Unfortunately, if not corrected, the lack of glutathione in turn accelerates the aging process.


Supplemental glutathione is expensive, and the effectiveness of oral formulas is questionable. To raise glutathione levels, it is better to supply the body with the raw materials it uses to make this compound: cysteine, glutamic acid, and glycine. The N-acetyl form of cysteine (N-acetylcysteine) is considered particularly effective for this purpose.

Glycine
Glycine retards muscle degeneration by supplying additional creatine, a compound that is present in muscle tissue and is utilized in the construction of DNA and RNA. Glycine is essential for the synthesis of nucleic acids, bile acids, and other nonessential amino acids in the body. It is used in many gastric antacid agents. Because high concentrations of glycine are found in the skin and connective tissues, it is useful for repairing damaged tissues and promoting healing.


Glycine is necessary for central nervous system function and a healthy prostate. It functions as an inhibitory neurotransmitter and as such can help prevent epileptic seizures. It has been used in the treatment of manic (bipolar) depression, and can also be effective for hyperactivity. Having too much of this amino acid in the body can cause fatigue, but having the proper amount produces more energy. If necessary, glycine can be converted into the amino acid serine in the body.

Histidine
Histidine is an essential amino acid that is significant in the growth and repair of tissues. It is important for the maintenance of the myelin sheaths that protect nerve cells, and is needed for the production of both red and white blood cells. Histidine also protects the body from radiation damage, aids in removing heavy metals from the system, and may help in the prevention of AIDS. Histidine levels that are too high may lead to stress and even psychological disorders such as anxiety and schizophrenia; people with schizophrenia have been found to have high levels of histidine in their bodies. Inadequate levels of histidine may contribute to rheumatoid arthritis and may be associated with nerve deafness. Methionine has the ability to lower histidine levels.

Histamine, an important immune system chemical, is derived from histidine. Histamine aids in sexual arousal. Because the availability of histidine influences histamine production, taking supplemental histidine—together with vitamins 83 (niacin) and Be (pyridoxine), which are required for the transformation from histidine to histamine—may help improve sexual functioning and pleasure. Because histamine also stimulates the secretion of gastric juices, histidine may be helpful for people with indigestion resulting from a lack of stomach acid. Persons with manic (bipolar) depression should not take supplemental histidine unless a deficiency has been identified. Natural sources of histidine include rice, wheat, and rye.

Isoleucine
Isoleucine, one of the essential amino acids, is needed for haemoglobin formation and also stabilizes and regulates blood sugar and energy levels. It is metabolized in muscle tissue. It is one of the three branched-chain amino acids. These amino acids are valuable for athletes because they enhance energy, increase endurance, and aid in the healing and repair of muscle tissue.


Isoleucine has been found to be deficient in people suffering from many different mental and physical disorders. A deficiency of isoleucine can lead to symptoms similar to those of hypoglycaemia. Food sources of isoleucine include almonds, cashews, chicken, chickpeas, eggs, fish, lentils, liver, meat, rye, most seeds, and soy protein. It is also available in supplemental form. Supplemental isoleucine should always be taken with a correct balance of the other two branched-chain amino acids, leucine and valine—approximately 2 milligrams each of leucine and valine for each milligram of isoleucine. Combination supplements that provide all three of the branched-chain amino acids are available and may be more convenient to use.

Leucine
Leucine is an essential amino acid and one of the branched-chain amino acids (the others are isoleucine and valine). These works together to protect muscle and act as fuel. They promote the healing of bones, skin, and muscle tissue, and are recommended for those recovering from surgery. Leucine also lowers elevated blood sugar levels, and aids in increasing growth hormone production. Natural sources of leucine include brown rice, beans, meat, nuts, soy flour, and whole wheat. Supplemental L-leucine must be taken in balance with L-isoleucine and L-valine (see Isoleucine in this section), and it should be taken in moderation, or symptoms of hypoglycaemia may result. An excessively high intake of leucine may also contribute to pellagra, and may increase the amount of ammonia present in the body.

Lysine
Lysine is an essential amino acid that is a necessary building block for all protein. It is needed for proper growth and bone development in children; it helps calcium absorption and maintains a proper nitrogen balance in adults. This amino acid aids in the production of antibodies, hormones, and enzymes, and helps in collagen formation and tissue repair. Because it helps to build muscle protein, it is good for those recovering from surgery and sports injuries. It also lowers high serum triglyceride levels. Another very useful ability of this amino acid is its capacity for fighting cold sores and herpes viruses. Taking supple mental L-lysine, together with vitamin C with bioflavonoid, can effectively fight and/or prevent herpes outbreaks, especially if foods containing the amino acid arginine are avoided.


Lysine is an essential amino acid, and so cannot be manufactured in the body. It is therefore vital that adequate amounts be included in the diet. Deficiencies can result in anaemia, bloodshot eyes, enzyme disorders, hair loss, an inability to concentrate, irritability, lack of energy, poor appetite, reproductive disorders, retarded growth, and weight loss. Food sources of lysine include cheese, eggs, fish, lima beans, milk, potatoes, red meat, soy products, and yeast.

Methionine
Methionine is an essential amino acid that assists in the breakdown of fats, thus helping to prevent a build-up of fat in the liver and arteries that might obstruct blood flow to the brain, heart, and kidneys. The synthesis of the amino acids cysteine and taurine may depend on the availability of methionine. This amino acid helps the digestive system; helps to detoxify harmful agents such as lead and other heavy metals; helps diminish muscle weakness, prevent brittle hair, and protect against radiation; and is beneficial for people with osteoporosis or chemical allergies.

It is useful also in the treatment of rheumatic fever and toxemia of pregnancy. Methionine is a powerful antioxidant. It is a good source of sulfur, which inactivates free radicals. It is also good for people with Gilbert's syndrome, an anomaly of liver function, and is required for the synthesis of nucleic acids, collagen, and proteins found in every cell of the body. It is beneficial for women who take oral contraceptives because it promotes the excretion of oestrogen. It reduces the level of histamine in the body, which can be useful for people with schizophrenia, whose histamine levels are typically higher than normal. As levels of toxic substances in the body increase, the need for methionine increases.

The body can convert methionine into the amino acid cysteine, a precursor of glutathione. Methionine thus protects glutathione; it helps to prevent glutathione depletion if the body is overloaded with toxins. Since glutathione is a key neutralizer of toxins in the liver, this protects the liver from the damaging effects of toxic compounds. An essential amino acid, methionine is not synthesized in the body, and so must be obtained from food sources or from dietary supplements. Good food sources of methionine include beans, eggs, fish, garlic, lentils, meat, onions, soybeans, seeds, and yogurt. Because the body uses methionine to derive a brain food called choline, it is wise to supplement the diet with choline or lecithin (which is high in choline) to ensure that the supply of methionine is not depleted.

Ornithine
Ornithine helps to prompt the release of growth hormone, which promotes the metabolism of excess body fat. This effect is enhanced if ornithine is combined with arginine and carnitine. Ornithine is necessary for proper immune system and liver function. This amino acid also detoxifies ammonia and aids in liver regeneration. High concentrations of ornithine are found in the skin and connective tissue, making it useful for promoting healing and repairing damaged tissues. Ornithine is synthesized in the body from arginine, and in turn serves as the precursor of citrulline, proline, and glutamic acid. Supplemental L-ornithine should not be taken by children, pregnant women, nursing mothers, or anyone with a history of schizophrenia, unless they are specifically directed to do so by a physician.

Phenylalanine Phenylalanine is an essential amino acid. Once in the body, it can be converted into another amino acid, tyrosine, which in turn is used to synthesize two key neurotransmitters that promote alertness: dopamine and norep-inephrine. Because of its relationship to the action of the central nervous system, this amino acid can elevate mood, decrease pain, aid in memory and learning, and suppress the appetite. It can be used to treat arthritis, depression, menstrual cramps, migraines, obesity, Parkinson's disease, and schizophrenia. Phenylalanine is available in three different forms, designated L-, D-, and DL-. The L- form is the most common type, and is the form in which phenylalanine is incorporated into the body's proteins. The D- type acts as a painkiller.

The DL-form is a combination of the D- and the L-. Like the D- form, it is effective for controlling pain, especially the pain of arthritis; like the L- form, it functions as a building block for proteins, increases mental alertness, suppresses the appetite, and helps people with Parkinson's disease. It has been used to alleviate the symptoms of premenstrual syndrome (PMS) and various types of chronic pain. Supplemental phenylalanine should not be taken by pregnant women or by people who suffer from anxiety attacks, diabetes, high blood pressure, phenylketonuria (PKU), or pre-existing pigmented melanoma, a type of skin cancer.

Proline
Proline improves skin texture by aiding in the production of collagen and reducing the loss of collagen through the aging process. It also helps in the healing of cartilage and the strengthening of joints, tendons, and heart muscle. It works with vitamin C to promote healthy connective tissue. Proline is obtained primarily from meat sources.

Serine
Serine is needed for the proper metabolism of fats and fatty acids, the growth of muscle, and the maintenance of a healthy immune system. It aids in the production of immunoglobulin and antibodies. Serine can be synthesized from glycine in the body. It is included as a natural moisturizing agent in many cosmetics and skin care preparations.

Taurine
High concentrations of taurine are found in the heart muscle, white blood cells, skeletal muscle, and central nervous system. It is a building block of all the other amino acids as well as a key component of bile, which is needed for the digestion of fats, the absorption of fat-soluble vitamins, and the control of serum cholesterol levels. Taurine can be useful for people with atherosclerosis, edema, heart disorders, hypertension, or hypoglycaemia.

It is vital for the proper utilization of sodium, potassium, calcium, and magnesium, and it has been shown to play a particular role in sparing the loss of potassium from the heart muscle. This helps to prevent the development of potentially dangerous cardiac arrhythmias. Taurine has a protective effect on the brain, particularly when the brain is dehydrated. It is used to treat anxiety, epilepsy, hyperactivity, poor brain function, and seizures. Taurine is found in concentrations up to four times greater in the brains of children than in those of adults. It may be that a deficiency of taurine in the developing brain is involved in epileptic attacks. Zinc deficiency also is commonly found in people with epilepsy, and this may play a part in the deficiency of taurine.

Taurine is also associated with zinc in maintaining eye function; a deficiency of both may impair vision. Taurine supplementation may benefit children with Down syndrome and muscular dystrophy. This amino acid is also used in some clinics for breast cancer treatment.


Excessive losses of taurine through the urine can be caused by many metabolic disorders. Cardiac arrhythmias, disorders of platelet formation, intestinal problems, an overgrowth of Candida, physical or emotional stress, a zinc deficiency, and excessive consumption of alcohol are all associated with high urinary losses of taurine. Excessive alcohol consumption also causes the body to lose its ability to utilize taurine properly. Diabetes increases the body's requirements for taurine; conversely, supplementation with taurine and cystine may decrease the need for insulin.


Taurine is found in eggs, fish, meat, and milk, but not in vegetable proteins. It can be synthesized from cysteine in the liver and from methionine elsewhere in the body, as long as sufficient quantities of vitamin B6 are present. For vegetarians, synthesis by the body is crucial. For individuals with genetic or metabolic disorders that prevent the synthesis of taurine, taurine supplementation is required.

Threonine
Threonine is an essential amino acid that helps to maintain the proper protein balance in the body. It is important for the formation of collagen and elastin, and aids liver and lip tropic function when combined with aspartic acid and methionine. Threonine is present in the heart, central nervous system, and skeletal muscle, and helps to prevent fatty build-up in the liver. It enhances the immune system by aiding in the production of antibodies. Because the threonine content of grains is low, vegetarians are more likely than others to have deficiencies.

Tryptophan
Tryptophan is an essential amino acid that is necessary for the production of vitamin 63 (niacin). It is used by the brain to produce serotonin, a necessary neurotransmitter that transfers nerve impulses from one cell to another and is responsible for normal sleep. Consequently, tryptophan helps to combat depression and insomnia and to stabilize moods. It helps to control hyperactivity in children, alleviates stress, is good for the heart, aids in weight control by reducing appetite, and enhances the release of growth hormone. It is good for migraine headaches, and may reduce some of the effects of nicotine. A sufficient amount of vitamin B6 (pyridoxine) is necessary for the formation of tryptophan, which, in turn, is required for the formation of serotonin.

A lack of tryptophan and magnesium may contribute to coronary artery spasms. The best dietary sources of tryptophan include brown rice, cottage cheese, meat, peanuts, and soy protein. In November of 1989, the U.S. Centres for Disease Control (CDC) reported evidence linking L-tryptophan supplements to a blood disorder called eosino-philia-myalgia syndrome (EMS). Several hundred cases of this illness—which is characterized by an elevated white blood cell count and can also cause such symptoms as fatigue, muscular pain, respiratory ailments, edema, and rash—were reported, and at least one death was attributed to the outbreak. After the CDC established an association between the blood disorder and products containing L-tryptophan in New Mexico, the U.S. Food and Drug Administration first warned consumers to stop taking L-tryptophan supplements, then recalled all products in which L-tryptophan was the sole or a major component. Subsequent research showed that it was contaminants in the supplements, not the tryptophan, that was probably responsible for the problem, but tryptophan supplements are still banned from the market in the United States.

Tyrosine
Tyrosine is a precursor of the neurotransmitters norep-inephrine and dopamine, which regulate mood, among other things. Tyrosine acts as a mood elevator; a lack of adequate amounts of tyrosine leads to a deficiency of norepinephrine in the brain, which in turn can result in depression. It suppresses the appetite and helps to reduce body fat. It aids in the production of melanin (the pigment responsible for skin and hair colour) and in the functions of the adrenal, thyroid, and pituitary glands. It is also involved in the metabolism of the amino acid phenylalanine.


Tyrosine attaches to iodine atoms to form active thyroid hormones. Not surprisingly, therefore, low plasma levels of tyrosine have been associated with hypothyroidism. Symptoms of tyrosine deficiency can also include low blood pressure, low body temperature (such as cold hands and feet), and restless leg syndrome.
Supplemental L-tyrosine has been used for stress reduction, and research suggests it may be helpful against chronic fatigue and narcolepsy. It has been used to help individuals suffering from anxiety, depression, allergies, and headaches, as well as persons undergoing withdrawal from drugs. It may also help people with Parkinson's disease.
Natural sources of tyrosine include almonds, avocados, bananas, dairy products, lima beans, pumpkin seeds, and sesame seeds. Tyrosine can also be produced from phenylalanine in the body. Supplements of L-tyrosine should be taken at bedtime or with a high-carbohydrate meal so that it does not have to compete for absorption with other amino acids.


Persons taking monoamine oxidase (MAO) inhibitors commonly prescribed for depression must strictly limit their intake of foods containing tyrosine and should not take any supplements containing L-tyrosine, as it may lead to a sudden and dangerous rise in blood pressure. Anyone who takes prescription medication for depression should discuss necessary dietary restrictions with his or her physician.

Valine
Valine, an essential amino acid, has a stimulant effect. It is needed for muscle metabolism, tissue repair, and the maintenance of a proper nitrogen balance in the body. Valine is found in high concentrations in muscle tissue. It is one of the branched-chain amino acids, which means that it can be used as an energy source by muscle tissue. It is good for correcting the type of severe amino acid deficiencies that can be caused by drug addiction. An excessively high level of valine ma lead to such symptoms as a crawling sensation in the ski: and even hallucinations.


Dietary sources of valine include dairy products grains, meat, mushrooms, peanuts, and soy protein. Supplemental L-valine should always be taken in balance wit the other branched-chain amino acids, L-isoleucine an L-leucine (see Isoleucine in this section).