Amino Acids
The Essential Role of Amino Acids in Health and Nutrition
Alanine
Alanine plays a major role in the transfer of nitrogen from peripheral tissue to the liver. It aids in the metabolism of glucose, a simple carbohydrate that the body uses for energy. It also guards against the buildup of toxic substances that are released in the muscle cells when muscle protein is broken down to quickly meet energy needs, such as happens with aerobic exercise. 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 B5) and coenzyme A, a vital catalyst in the body. Research has found that for people with insulin-dependent diabetes, taking an oral dose of L-alanine can be more effective than a conventional bedtime snack in preventing nighttime hypoglycemia.
Arginine
Arginine retards the growth of tumors and cancer by enhancing immune function. It increases the size and activity of the thymus gland, which manufactures T lymphocytes (T cells), crucial immune system components. 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. It may reduce the effects of chronic alcohol toxicity. 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 the healing and repair of damaged tissue.
Arginine is important for muscle metabolism. It helps to maintain a proper nitrogen balance by acting as a vehicle for transportation and storage and aiding in the excretion of excess nitrogen. Studies have shown that it also reduces nitrogen losses in people who have undergone surgery and improves the function of cells in lymphatic tissue. This amino acid aids in weight loss by facilitating 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 comprises collagen rich in arginine. Various functions, including insulin production, glucose tolerance, and liver lipid metabolism, are impaired if 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. It is, therefore, deemed essential early in life. Foods high in arginine include carob, chocolate, coconut, dairy products, gelatin, meat, oats, peanuts, soybeans, walnuts, white flour, wheat, and wheat germ.
People with viral infections such as herpes should not take supplemental arginine. They should avoid foods rich in arginine and low in the amino acid lysine (see below), as this 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, created from another amino acid, aspartic acid, is needed to maintain balance in the central nervous system; it prevents you from being either overly nervous or overly calm. As it is converted back into aspartic acid, asparagine releases energy that brain and nervous system cells use for metabolism. It promotes the process by which one amino acid is transformed into another in the liver.
Aspartic Acid
Because aspartic acid increases stamina, it is good for fatigue and depression and plays a vital role in metabolism. Chronic fatigue may result from low levels of aspartic acid because this leads to lowered cellular energy. In proper balance, aspartic acid is beneficial for neural and brain disorders; it has been found in increased levels in persons with epilepsy and in decreased levels in people with some types of depression. It is good for athletes and helps protect the liver by aiding in removing excess ammonia. Aspartic acid combines with other amino acids to form molecules that absorb toxins and remove them from the bloodstream. It helps to move certain minerals across the intestinal lining and into the blood and cells, aids cell function, and aids 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 those found in sprouting seeds, contains abundant aspartic acid. The artificial sweetener aspartame is made from aspartic acid and phenylalanine, another amino 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, mainly in the mitochondria, 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 buildup, especially in the heart, liver, and skeletal muscles. Carnitine may be useful in treating chronic fatigue syndrome (CFS) because a disturbance in the function of the mitochondria (the site of energy production within the cells) may be a fatigue factor. Studies have shown decreased carnitine levels in many people with CFS.
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. According to The American Journal of Cardiology, one study showed that propionyl-L-carnitine, a carnitine derivative, helps to ease the severe pain of intermittent claudication, a condition in which a blocked artery in the thigh decreases the supply of blood and oxygen to leg muscles, causing pain, especially with physical activity. Carnitine has the ability to lower blood triglyceride levels, aid in weight loss, improve the motility of sperm and improve muscle strength in people with neuromuscular disorders. It may be useful in treating Alzheimer's disease. Conversely, 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. It works with antioxidants to help slow the aging process by promoting the synthesis of carnitine acetyl-transferase, an enzyme in the mitochondria of brain cells that is vital for producing cellular energy there.
The body can manufacture carnitine if sufficient amounts of iron, vitamin B1 (thiamine), vitamin B6 (pyridoxine), 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 deficiency symptoms 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 nonvegetarians 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, are 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, and DL-carnitine. DLcarnitine is not recommended, as it may cause toxicity. Acetyl-L-carnitine (ALC), a carnitine derivative produced naturally in the body, is involved in carbohydrate and protein metabolism and in the transport of fats into the mitochondria. It increases levels of carnitine in tissues and even surpasses the metabolic potency of carnitine. ALC has become one of the most studied compounds for its anti-aging effects, particularly with regard to degeneration of the brain and nervous system. Several major studies have shown that daily supplementation with ALC significantly slows the progression of Alzheimer's disease, resulting in less deterioration in memory, attention and language, and spatial abilities. It also can be used to treat other cognitive disorders, as well as depression.
ALC provides numerous other benefits to many of the body's systems. It helps to limit damage caused by oxygen starvation, enhance the immune system, protect against oxidative stress, stimulate the antioxidant activity of certain enzymes, protect membranes, slow cerebral aging, prevent nerve disease associated with diabetes and sciatica, modulate hormonal changes caused by physical stress, and increase the performance-enhancing benefits of branched
chain amino acids.
Total brain levels of ALC (and carnitine) decline with age. In most of the studies of ALC done with humans, subjects took 500 to 2,500 milligrams daily in divided doses. No toxic or serious side effects have been reported.
Citrulline
The body makes citrulline from another amino acid, ornithine. Citrulline promotes energy, stimulates the immune system, is metabolized to form L-arginine, and detoxifies ammonia, which damages living cells. Citrulline is found primarily in the liver. It is helpful in treating fatigue.
Cysteine and Cystine
These two amino acids are closely related; each cystine molecule consists of two cysteine molecules joined together. Cysteine is very unstable and easily converted to L-cystine; however, each form can be converted 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 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 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 a 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-methionine in the body. Vitamin B6, vitamin B12, and folate are 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-acetylcysteine, or NAC) may be used in place of L-cysteine. NAC 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 antiaging effect on the body, reducing the accumulation of age spots, for example. NAC 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. Numerous medicinal herbs contain therapeutic amounts of flavonoids, which are often a major component of an herb's medicinal activity.
Gamma-Aminobutyric Acid
Gamma-aminobutyric 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 overfiring. Together with niacinamide and inositol, it prevents anxiety- and stress-related messages from reaching the brain's motor centers 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 and may reduce cravings for alcohol. It is also thought to promote growth hormone secretion.
Too much GABA, however, can cause increased anxiety, shortness of breath, numbness around the mouth, and tingling in the extremities. Further, abnormal levels of GABA unbalance the brain's message-delivery system and may cause seizures.
Glutamic Acid
Glutamic acid is an excitatory neurotransmitter that increases neurons firing in the central nervous system. It is a major excitatory neurotransmitter in the brain and spinal cord. It is converted into either glutamine or GABA.
This amino acid is important in the metabolism of sugars and fats and aids in the transportation of potassium into the spinal fluid and 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 behavioral disorders. It is used in the treatment of epilepsy, mental retardation, muscular dystrophy, ulcers, and hypoglycemic coma, a complication of insulin treatment for diabetes. It is a component of folate (folic acid), a B vitamin that helps the body break down amino acids. Because one of its salts is monosodium glutamate (MSG), glutamic acid should be avoided by anyone allergic to MSG.
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 may be released. As a result, stress and/ or illness can lead to the loss of skeletal muscle. However, if enough glutamine is available, this can be prevented.
Supplemental L-glutamine can be helpful in the treatment of arthritis, autoimmune diseases, fibrosis, intestinal disorders, 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, depression, schizophrenia, and senility. It preserves glutathione in the liver and protects that organ from the effects of acetaminophen overdose. It enhances antioxidant protection. 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. However, because of its close relationship to these amino acids, 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 appears to exert anti-aging effects, aiding in the breakdown of oxidized fats that may contribute to atherosclerosis. It can mitigate some of the damage caused by tobacco smoke because it modifies the harmful effects of aldehydes, chemicals present in cigarette smoke that damage cells and molecules, and it may protect the liver from alcohol-induced damage.
A glutathione deficiency first affects the nervous system, causing symptoms such 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. A study sponsored in part by the National Cancer Institute found that people with HIV disease who had low glutathione levels had a lower survival rate over a three-year period than those whose glutathione levels were normal. 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 (NAC), 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. It improves glycogen storage, thus freeing up glucose for energy needs. 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, which protect nerve cells and is needed for the production of both red and white blood cells. Histidine also protects the body from radiation damage, helps lower blood pressure, 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 B3 (niacin) and B6 (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.
Homocysteine
Homocysteine is an amino acid that is produced in the body in the course of methionine metabolism. This amino acid has been the focus of increasing attention in recent years because high levels of homocysteine in the blood are associated with an increased risk of cardiovascular disease. Further, it is known that homocysteine has a toxic effect on cells lining the arteries, makes the blood more prone to clotting, and promotes the oxidc:.tion of low-density lipoproteins (LDL, the so-called "bad cholesterol"), which makes it more likely that cholesterol will be deposited as plaque in the blood vessels.
Like other amino acids, homocysteine does perform a necessary function in the body. It is then usually broken down quickly into the amino acid cysteine and other important compounds, including adenosine triphosphate (ATP, an important source of cellular energy) and S-adenosylmethionine (SAMe). However, a genetic defect or, more commonly, deficiencies of vitamins B6 and B12 and folate (folic acid) can prevent homocysteine from converting rapidly enough. As a result, high levels of the amino acid accumulate in the body, damaging cell membranes and blood vessels and increasing the risk of cardiovascular disease, particularly atherosclerosis. Vitamins B6 and B12 and folate work together to facilitate the breakdown of homocysteine and thus help protect against heart disease.
Isoleucine
Isoleucine is an essential amino acid that is needed for hemoglobin formation and stabilizes and regulates blood sugar and energy levels. It is metabolized in muscle tissue and 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 hypoglycemia.
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 L-isoleucine should always be taken with a correct balance of the other two branched-chain amino acids, L-leucine, and L-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 branchedchain amino acids (the others are isoleucine and valine). These work together to protect muscles 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 hypoglycemia 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 proteins. 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 herpesviruses. Taking supplemental L-lysine, together with vitamin C with bioflavonoids, can effectively fight and/ or prevent herpes outbreaks, especially if foods containing the amino acid arginine are avoided (see HERPESVIRUS INFECTION in Part Two). Supplemental L-lysine also may decrease acute alcohol intoxication.
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 anemia, 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 buildup 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, detoxifies harmful agents such as lead and other heavy metals, helps diminish muscle weakness, prevents brittle hair, and protects 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 and helps to prevent skin and nail problems. 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 estrogen. 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. Because it can cross the blood-brain barrier, it can have a direct effect on brain chemistry. Once in the body, phenylalanine can be converted into another amino acid, tyrosine, which in turn is used to synthesize two key neurotransmitters that promote alertness: dopamine and norepinephrine. 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 Dform, 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, as well as products containing aspartame (an artificial sweetener made from phenylalanine and another amino acid, aspartic acid), should not be taken by pregnant women or by people who suffer from anxiety attacks, diabetes, high blood pressure, phenylketonuria (PKU), or preexisting 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, dairy products, and eggs.
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 is a component of brain proteins and the protective myelin sheaths that cover nerve fibers. It is important in RNA and DNA function, cell membrane formation, and creatine synthesis. It also aids in the production of immunoglobulins and antibodies. However, too-high serine levels in the body may have adverse effects on the immune system.
Serine can be made from glycine in the body, but this process requires the presence of sufficient amounts of vitamins B3 and B6 and folic acid. Food sources of serine include meat and soy foods, as well as many foods that often cause allergic reactions, such as dairy products, wheat gluten, and peanuts. It is included as a natural moisturizing agent in many cosmetics and skin care preparations.
Taurine
High taurine concentrations 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 hypoglycemia. 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 if 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 adults. It may be that a deficiency of taurine in the developing brain is involved in seizures. Zinc deficiency is also 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. Ta urine 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. Taurine supplementation may reduce symptoms of alcohol withdrawal. 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, elastin, and tooth enamel and aids liver and lipotropic function when combined with aspartic acid and methionine. A precursor of the amino acids glycine and serine, threonine is present in the heart, central nervous system, and skeletal muscle, and helps to prevent fatty buildup in the liver. It enhances the immune system by aiding in the production of antibodies and may be helpful in treating some types of depression.
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 B3 (niacin). The brain uses it 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. Sufficient amounts of vitamins B6 (pyridoxine) and C, folate, and magnesium are necessary for the formation of tryptophan, which, in turn, is required for the formation of serotonin. A study reported in the Archives of General Psychiatry found that women with a history of bulimia nervosa, an eating disorder, experienced relapses after they took an amino acid mixture lacking tryptophan. Researchers believe that insufficient tryptophan altered brain serotonin levels and, consequently, the transmission of nerve impulses. 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. This amino acid is not available in supplement form in the United States. In November of 1989, the U.S. Centers for Disease Control (CDC) reported evidence linking L-tryptophan supplements to a blood disorder called eosinophiliamyalgia syndrome (EMS). Several hundred cases of this illness are characterized by an elevated white blood cell count and can also cause such symptoms as fatigue, muscular pain, respiratory ailments, edema, and rashwere reported. 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 (FDA) 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 were probably responsible for the problem, but tryptophan supplements are still banned from the market in the United States. According to the FDA, at least thirty-eight deaths were attributable to the tryptophan supplements.
Tyrosine
Tyrosine is important to overall metabolism. It is a precursor of adrenaline and the neurotransmitters norepinephrine and dopamine, which regulate mood and stimulate metabolism and the nervous system. 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 also acts as a mild antioxidant, suppresses the appetite, and helps to reduce body fat. It aids in the production of melanin (the pigment responsible for skin and hair color) 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, low sex drive, 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 may be helpful in treating liver and gallbladder disease, and 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 may lead to such symptoms as a crawling sensation in the skin 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 with the other branched-chain amino acids, L-isoleucine and L-leucine (see Isoleucine in this section).
The Ultimate Guide to Amino Acids
Amino Acids: Building Blocks of Life
Amino acids are chemical compounds that form the foundation of proteins, the structural and functional molecules essential for all living organisms. From muscle development to brain communication, amino acids are indispensable for maintaining optimal health.
Why Are Amino Acids Important?
Proteins, composed of amino acids, perform critical roles in the body:
Building and repairing tissues like muscles, ligaments, and tendons.
Supporting the immune system and metabolic processes.
Regulating water balance and maintaining pH levels.
Producing enzymes and hormones for various bodily functions.
Amino acids also act as precursors for neurotransmitters, facilitating communication within the nervous system.
Types of Amino Acids
Essential Amino Acids:
These must be obtained through diet as the body cannot synthesize them. They include:
Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan, Valine
Non-Essential Amino Acids
These are synthesized by the body but are equally crucial. Examples include alanine, arginine, and tyrosine.Conditionally Essential Amino Acids
Under certain conditions, non-essential amino acids like cysteine and tyrosine become essential if their precursors (methionine and phenylalanine) are deficient.
Dietary Sources of Amino Acids
Amino acids are found in a variety of foods:
Animal sources: Eggs, lean meats, fish, and dairy products.
Plant sources: Soy, quinoa, lentils, and nuts.
For vegetarians and vegans, a balanced intake of diverse plant-based foods ensures all essential amino acids are met.
Amino Acid Supplements
Supplementing with amino acids can be beneficial for specific needs:
Branched-chain amino acids (BCAAs): Boost muscle recovery and energy.
Free-form amino acids: Provide immediate absorption into the bloodstream.
Usage Tips
Take supplements on an empty stomach for better absorption.
Pair with vitamins B6 and C to enhance effectiveness.
Avoid excessive doses to prevent potential toxicity.
Conclusion
Amino acids are more than the building blocks of proteins—they are vital for life itself. Whether through diet or supplementation, ensuring a steady supply of these nutrients supports overall health, energy, and longevity.