Nutrition is a most important factor affecting health and disease. Of the six nutrients, carbohydrates, fats and proteins have probably received the most attention. They are an indispensible constituent of all living cells and are the main components of enzymes, antibodies, muscle and connective tissue, hair, blood haemoglobin, some hormones, skin and so on. About three quarters of the body's dry weight is made up of protein, with over 100,000 different kinds.

Proteins are made up of amino acids - the building blocks, and the particular combination of amino acids in a protein determines its properties. There are only 20 kinds normally required. Many proteins are also combined with other molecules to make specialised materials such as glycroproteins like mucous, and lipoproteins in membranes.

Amino acids are coming to be recognised as being no less important than vitamins and minerals when it comes to supplementation. Amino acids are made of carbon, hydrogen, oxygen, nitrogen and in some cases sulphur. They always contain an amino group (NH2) and an acid group (COOH) with a variable group that determines which amino acid it is and with what properties. They ca`n bond together in chains called peptides or long chains called polypeptides. Amino acids have left or right handed forms, indicated by D (Latin dextro) or L (laevo). Natural amino acids are an L-form. Some D-forms do have special properties, such as D-Phenylalanine (DLPA), which can be valuable.

The human body can synthesize many amino acids from dietary components and they are called non-essential amino acids. The essential amino acids must be obtained from the diet like most vitamins. However, all the amino acids are essential in the sense of being vital for making proteins.

Non-essential amino acids - Cysteine (or Cystine), Tyrosine, Arginine, Alanine, Glutamic Acid, Proline (or Hydroxyproline), Glutamine, Histidine, Aspartic Acid, Glycine, Serine, Asparginine. Essential amino acids -Tryptophan, Isoleucine, Lysine, Threonine, Leuchine, Methionine, Phenylalanine, Valine (all L-form).

The amino acids are present in food in varying proportions, and it is well possible for the diet to be deficient in one or more amino acids. Amino acid supplements may be in tablet or capsule form, as salts or pure amino acids. The latter are more expensive but more biologically active. They should be taken with water on an empty stomach.

These are some of the properties of particular amino acids:

• L-Arginine stimulates growth hormone secretion, so it is important for growing children.
• L-Cysteine is a powerful antioxidant, binding to free radicals. It is part of the tripeptide Glutathione which has detoxicant properties,and it is needed to produce Coenzyme A and for hair formation. L-Cystine is related, but lacks the antioxidant properties. Diabetics should use L-Cysteine with caution as it blocks insulin activity.
• L-Glutamine is involved in a lot of metabolic processes. L-Glutamic Acid is formed in the brain from L-Glutamine Acid and then it is an important energy source to the brain. L-Glutamine also helps control alcohol craving in alcoholics.
• L-Histidine is a forerunner of Histamine which is involved in smooth muscle contraction and vasodilation, neurotransmission and gastric secretion. It has been found to be helpful in treating rheumatoid arthritis.
• L-Lysine is often only available in limited amounts in vegetarian diets. It is important for optimal growth in children and is valuable in controlling the herpes virus (cold sores etc) along with Vitamin C.
• L-Methionine deficiency may result in anaemia. It is needed in the production of lecithin and it is the limiting amino acid in many foods, including soya beans, peanuts and potatoes.
• L-Ornithine is not built into protein but it is metabolically important. it stimulates secretion of growth hormones and is important in wound healing and the immune system.
• L-Phenylalanine is involved in neurotransmitters which themselves have many vital roles. It is used for appetite control and can be stimulative to the brain and body. DLPA has value in pain management.
• Taurine (it has no D/L versions) is another amino acid which is not found in proteins. It may be needed for low birth weight infants receiving cows milk It appears to be involved in proper heart function.
• L-Trypotophan is often deficient in diets. It can be used for sleeping disorders and mood stabilisation.