Information about proteins, their significance in our diet, the constituents of proteins i.e. amino acids, protein quality and the functions of proteins.


Proteins are broken down into their constituent amino acids during digestion and absorbed in this form. The main source of nitrogen to the body is dietary protein. Absence of dietary protein in the food may cause the body to go into negative nitrogen balance. The reason behind this is that amino acids are constantly used up by the body to form enzymes, hormones and cell proteins. This is accompanied by the formation of nitrogenous wastes that are excreted out of the body by the kidneys.

Amino acids
Amino acids are made up of carbon, hydrogen, oxygen and nitrogen. Some of the amino acids also contain other minerals like iron, copper, zinc, iodine, sulfur and phosphate. Amino acids are divided into essential and non-essential amino acids groups.

Essential amino acids cannot be synthesized by the body. For this reason, it is important to include them in diet. Non-essential amino acids can be synthesized in the body.

The nutritional value of proteins depends upon the amino acids that are present in them.

Complete proteins
Protein foods that contain all the essential amino acids in the correct proportion are called complete proteins. Complete proteins are usually derived from animals sources and include meat, fish, eggs,soya beans and milk products.

Protein quality
The nutritional value of proteins is measured by how well it meets the nutritional requirement of the body. High quality protein is usually of animal origin and is easily digested. It contains all the essential amino acids in the correct proportion as required by the body. Protein quality is measured by feeding it to animals and then by measuring how much quantity of protein is retained in the body for growth and repair. The amount of protein retained in the body is called biological value. A balanced diet can be achieved by eating a range of foods containing low-quality proteins, provided that deficiencies in amino acid content of any one constituent proteins of the diet is supplied by another.

Functions of proteins
Amino acids are used for:
Growth and repair of body cells and tissues
Synthesis of enzymes, plasma proteins, antibodies and some hormones
Provision of energy
When protein is eaten in excess of the body’s needs, the nitrogenous part is detached and excreted by the kidneys. The remained is converted into fat for storage in the fat cells of the adipose tissue. The removal of the nitrogenous part from amino acids is called deamination.

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