Proteins are an important part of our diet, but in a country like South Africa, some population groups eat too little, while others eat too much.
Many people are interested in boosting their protein intake to lose weight, to promote muscle growth and to improve their performance in sport.
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In this article DietDoc takes a look at the role that protein plays in our diets.
Basic chemistry
Proteins are very large molecules which consist of basic building blocks called amino acids. About 20 different amino acids have been identified in animal and plant proteins. Plants are in the lucky position that they are able to make all the amino acids they need for their protein needs from basic chemicals like carbon and nitrogen.
Animals, on the other hand, can’t produce amino acids and are dependent on dietary sources for their supply. Mammals, including humans can convert some of the amino acids they obtain from their diet to other amino acids in the liver. However, this ability is limited and there are certain amino acids which we cannot manufacture on our own.
Amino acids which cannot be manufactured in the human body are called ‘essential amino acids’ and we are totally dependent on dietary sources to obtain these essential components for making proteins in our bodies. Of the 20 amino acids that occur in nature, nine are classified as ‘essential’ for human beings.
Complete and incomplete protein
Protein obtained from animals, e.g. proteins found in meat, fish, milk, cheese, yoghurt, and eggs, contain all the essential amino acids which humans need for building new body tissues and repairing tissues that have been worn out or damaged. Because of their superior amino acid content, proteins derived from animals are called, 'complete' or 'high-quality proteins'.
Plant protein, e.g. proteins found in grains, cereals, legumes, fruit and vegetables, also contain amino acids, but most plant proteins are deficient in one or more of the essential amino acids. Consequently, protein derived from plant sources are classified as, 'incomplete' or 'low-quality protein'. Good examples of the lack of essential amino acids in plant proteins are maize proteins, which don’t contain the essential amino acid called lysine, and wheat proteins that are deficient in the essential amino acid called tryptophan.
While it is not necessary to eat only animal proteins, it stands to reason that we need to eat some protein derived from animals every day, particularly during periods of rapid growth and/or when our protein needs are high as in the case of wasting illnesses. This is where the great controversy over vegetarianism arises. - (Dr I.V. van Heerden, DietDoc)
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