Protein Requirements

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Protein

Protein is an essential part of the diet. Proteins are necessary for maintaining tissues and for sustaining growth. They are also used to make hormones and regulation of a wide range of bodily functions. It is made up of various combinations of small organic chemicals called amino acids. When we eat protein foods it is broken down during digestion into its constituent amino acids which are in turn absorbed by the blood capillaries and transported to the liver. The amino acids are then synthesized into proteins or stored as fat or glycogen for energy.

Amino Acids

Amino acids are the building blocks of protein. The body requires 20 different amino acids of which 8 are referred to as essential amino acids which cannot be synthesized by the human body. Animals and plants manufacture proteins that contain these essential amino acids. The body is capable of producing Non-essential amino acids sufficiently to meet the demands for growth and tissue repair. The essential Amino Acids are lsoleucine, Leucine, Lysine, Methionine, phenylalanine, Threonine, Tryptophan and Valine.The non-essential Amino Acids are: Alanine, Arginine, Asparagine, Aspartic acid, Cysteine, Clutamic acid, Clutamine, Glycine, Histidine*, Proline, Serine and Tyrosine.

• Histidine is essential for babies but not for adults.

Proteins form part of the structure of the body, so that a continual supply of amino acids is needed. Our bodies are able to put these basic amino acid units together, using different arrangements of amino acids, to produce specific proteins, which can only be produced if all the necessary amino acids are available.

The nutritional value of a protein food can be judged by its ability to provide both the quantity and number of essential amino acids needed by the body. Different food sources contain different groups of proteins, which are made up of different arrangements and amounts of amino acids. In general, proteins from animal sources are of greater nutritional value because they usually contain all the essential amino acids. Proteins from plant sources, such as cereals and vegetables, may be deficient in one or other of the essential amino acids. For example, the proteins obtained from wheat lack adequate quantities of one essential amino acid, and those from beans are deficient in another.

Cooking can alter the amino-acid composition of protein and this usually results in desirable flavour and browning development. Very little nutritional value is lost.

The recommended daily allowance:

Type of person	Amounts Required (g/day)
Infants/Children
0-12 months	12.5-14.9
1-3 yrs	14.50
4-10 yrs	19.7-28.3
Boys
11-14 yrs	42.1
15-18 yrs	55.2
Girls
11-14 yrs	41.2
15-18yrs	45
Men
19-50 yrs	55.5
50+ yrs	53.3
Women
19-50 yrs	45
50 + yrs	46.5
During pregnancy	extra 6g/day
Breast feeding 0-6mths	extra 11g/day
Breast feeding 6+ mths	extra 8g/day

How much protein we need to eat in our diet usually depends on our ideal body weight. Ideal body weight is used because amino acids are not needed by fat cells, only by our lean body mass.
Eating a little high protein food at each meal helps reduce the appetite plus the body uses energy to convert protein to carbohydrates, a process known as Gluconeogenesis.

However, eating excessive protein provides little benefit. Muscle mass does not increase simply by eating high protein foods. Protein intake significantly above the recommended values can prove harmful because excessive protein breakdown strains the liver and kidney functions through the production and elimination of urea and other solutes.

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