Food Data Chart

Protein is an essential part of the diet. It is made up of various combinations of small organic chemicals called amino acids. When we eat food containing protein it is broken down during digestion into its constituent amino acids. These amino acids are absorbed by our bodies and are used to produce new proteins and other necessary substances. Our bodies can make some of the amino acids needed to manufacture proteins, but others must be obtained from the diet; these are the eight so-called 'essential' amino acids. In addition, one other amino acid is needed by infants during early growth and development.

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.

Because the deficiency is different in each food, when they are eaten together they complement each other and the mixture is of higher nutritional value than the separate foods, and is as good as animal protein. It is important, particularly for strict vegetarians who do not consume dairy or egg products (see Figure 21), that a variety of different types of protein foods are eaten.

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.

RECOMMENDED DAILY DIETARY INTAKE OF PROTEIN IN AUSTRALIA

The recommended dietary intake (RDI) in Australia is one gram per kilogram of body weight per day. The protein intake for a 70-kilogram man is 70 grams and for a 58-kilogram woman, 58 grams per day. Growing children and pregnant and lactating women have a greater requirement for protein because of the additional needs of these conditions (see Figure 6). People who have had severe infections or surgery may require additional protein. Because of the margin of safety in the RDI for protein it is usually not necessary to increase protein intake for additional muscular activity such as required for heavy work or training.

A deficiency of protein in the diet can lead to muscle wasting, oedema, anaemia and, in children, a slowing or stopping of growth. These conditions are usually seen as a result of chronic protein malnutrition. Having an adequate energy intake (see Figure 11 and Figure 12) will almost always ensure an adequate protein intake.

Higher levels of protein consumption appear to be neither beneficial nor harmful. However, it is possible that additional calcium may be required to counterbalance an excessive protein intake. Also there is a higher load of protein breakdown products, which must be excreted by the kidneys.