Amino Acids

Amino acids are the structural units from which proteins are made. Commonly referred to as the building blocks of protein, amino acids make up 75 percent of the human body and are essential for almost every physiological function. Muscles, ligaments, tendons, organs, glands, nails, hair, body fluids, hormones and genes are all comprised of protein. It is also central to bone growth, the manufacture of neurotransmitters and the composition of antibodies that form the immune system.

Every chemical reaction taking place in the body depends on amino acids and proteins. The latter are complex molecules in which linear chains of amino acids link together in varying sequences to form a vast variety of proteins. The body uses amino acids to build the exact type of protein it needs. The make-up of each protein differs in dependence on the number and type of amino acids chemically bound together to create that particular protein. The combinations are specific and cannot occur if even one amino acid is missing or in short supply.

Protein is ingested from food sources. Complete proteins contain all eight essential amino acids and are found primarily in foods of animal origin such as meat, fish, eggs and dairy products. Incomplete proteins are mainly of plant origin – cereals and pulses, for example – and do not contain all essential amino acids. The combination of different plant sources, however, such as pulses and grains, forms complementary proteins that do contain all essential amino acids.

During digestion, proteins are broken down into their component amino acids which are absorbed through the intestinal wall into the bloodstream. These are transported around the body to be used for numerous important biological processes. Of the approximately 80 amino acids found in nature, 20 are necessary for proper human growth and function. In various combinations they create 50 000 different proteins and 20 000 enzymes.

Structure & Substance

All amino acids have a similar chemical structure – each contains an amino group (NH ₂ ), an acid group (COOH), a hydrogen atom (H) and a distinctive side-group that makes proteins more complex than either carbohydrates or lipids. All amino acids are attached to a central carbon atom (C).

The three-dimensional shape of proteins is derived from the sequence and properties of its amino acids and determines its function and interaction with other molecules. Each amino acid is joined to the next by a peptide bond, which is the name given to the link or attraction between the COOH end of one and the NH ₂ end of another. Proteins of various lengths are made when amino acids come together in this manner. A dipeptide is two amino acids joined by a peptide bond, while a tripeptide is three amino acids joined by peptide bonds. The unique shapes of proteins enable them to perform their various tasks in the body. Heat, acid, or other conditions can disturb proteins, causing them to uncoil or lose their shape and impairing their ability to function. This is referred to as denaturation.

Amino acids are made from the elements carbon, hydrogen, oxygen and nitrogen and some contain minerals including iron, copper, zinc, iodine, sulphur and phosphorus. They are classified as essential or non-essential.

Essential Amino Acids are those that must be supplied in the diet as the human body cannot manufacture them at all or cannot make them in sufficient quantity to meet its needs. These are phenylalanine, threonine, lysine, isoleucine, leucine, methionine, tryptophan, valine and histadine (considered essential in children but not in adults).

Non-essential Amino Acids are those the body can synthesise provided there is enough available nitrogen, carbon, hydrogen and oxygen. These are arginine, alanine, aspartic acid, asparagine, cysteine, cystine, glycine, glutamic acid, glutamine, praline, serine and tyrosine. They are required by the body but it is not essential that they are ingested in the diet as they can be manufactured from essential amino acids.

Deficiencies

The essential amino acids must be ingested every day as the body uses them continuously but does not store any surplus. An insufficient amount of even one essential amino acid can result in protein degradation, a depletion that can rapidly lead to disease.

An amino acid deficiency is usually caused by a diet that is low in protein, an improper or imbalanced diet or the inability to properly assimilate protein via the digestive system. Vegetarians and vegans are especially prone to amino acid deficiencies. Other factors such as infection, trauma, drug or medication use, stress, ageing and an inadequate supply of vitamins and minerals can also lead to deficiency.

There is some controversy regarding the correct intake of protein and amino acids. Those who especially need an adequate intake are children, the elderly, the infirm, people recuperating from injury or surgery, athletes and pregnant or lactating women. Those who could benefit from amino acid supplementation include people suffering from degenerative diseases, mental or nervous disorders, heart disease, chronic fatigue syndrome, diabetes, epilepsy and anaemia, as well as long-term vegans/vegetarians and those in alcohol/drug recovery.

Supplements are available singly or in combinations. The latter are sold as free-form amino acids which are considered the purest and are made from a grain base. They can be used individually in pills and capsules, in combination forms or powdered as used to make whey/soy protein drinks.

Side-Effects

Amino acid supplementation can be beneficial but does have the potential risk of side-effects. Taking single amino acids may cause an imbalance in other amino acids over an extended period of time: a supplement that contains a balance of amino acids may help to prevent this from occurring. Side-effects depend largely on the variant of amino acid: most are practically harmless and offer many benefits, while others such as tyrosine have in rare cases at higher doses been reported to cause restlessness, anxiety and rapid heartbeat. Other examples are:

• Arginine – a popular supplement among bodybuilders – may increase the production of growth hormones and promote growth of the herpes virus unless taken with ornithine.
• Phenylalanine comes in two forms, L-phenylalanine to treat depression and D-phenylalanine to control chronic pain. People with high blood pressure and those with the genetic disorder, phenylketonuria, must avoid taking L-phenylalanine. It can cause a stimulant effect that can contribute to insomnia and anxiety.
• Taurine is used to treat epilepsy: high doses may cause depression.

Three of the most important amino acids in the body are leucine, isoleucine and valine, collectively known as branched-chained amino acids (BCAA). They are most important for maintaining muscle tissues, preserving muscle glycogen stores and preventing muscle breakdown during strenuous exercise. Many people take BCAA supplements to enhance physical training and improve performance. Bodybuilding supplements contain a combination of amino acids to aid in building muscles and ease the transition after workout sessions.

There have apparently not been any reported side-effects with BCAA supplement intake: excess is usually converted to other amino acid forms, used up as energy or stored as fat. However, anyone suffering from liver or kidney disease should not take high doses of amino acids without first asking a doctor.

Certain amino acids taken in supplement form may aid in fighting heart disease, lowering blood pressure and providing protection against strokes. They are also thought to help in treating cancer, reducing sugar cravings, building immunity and protecting the body in various other ways. One should nonetheless proceed with caution when considering amino acid supplementation and always seek advice from a healthcare professional before taking high-dose single amino acids.

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