Functions of proteins

Proteins are essential for the growth, maintenance and repair of all body tissues. They also help to regulate water and acid/base balance in the body and are used to make hormones, enzymes and antibodies. Proteins can also be broken down to provide energy.

How much protein do you need?

The daily amount of protein needed to maintain good health and adequate growth cannot be specified exactly, but a generally recommended amount is one gram of protein for each kilogram of body weight. Thus a man who weighs 75 kg should consume 75 grams of protein each day. At the same time the overall diet should contain between 10 and 15 per cent protein. Infants and growing children need more protein than adults; women who are pregnant or breastfeeding also need extra protein, as does someone who has suffered an injury, such as a broken leg or serious burns, or who has undergone surgery. All of these people are building new tissue. When a diet is especially rich in protein foods there is a surplus of amino acids. These cannot be stored as such, but they can be converted to fat (adding to your weight problem!) or they can be broken down by the liver. In the latter case the nitrogen content is excreted through the kidneys in the form of urea in the urine, while the non-nitrogenous part is ‘burned’ in the tissues as a source of energy. Too little protein is a much more serious affair. Children who do not eat sufficient protein do not grow as quickly and, if the deficiency is prolonged, do not reach the same adult stature as those who receive an adequate diet. There is a protein deficiency disease called kwashiorkor that occurs when a child, often fed satisfactorily by mother’s milk, is suddenly weaned on to solids low in protein. The child’s muscles waste away while the body becomes bloated (oedema) with fluid that collects in the tissues. The liver also becomes damaged and, if the missing amino acids are not available in time, the child dies. Kwashiorkor is rare in the Western world, but is only too common in the Third World countries where many children live on monotonous diets adequate in calories yet deficient in good-quality protein.

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