The word “protein” is derived from the Greek word “proteios”, which means primary or holding first place. The way name suggest this group of components are the most important cell constituent. Protein is present in all cells of the body. It is present in variable level in different tissues of the body like muscles contain about 20% where as in blood plasma it is 7%.
In the body, protein plays an important role in the biochemical, biophysical and physiological processes. Protein is required for all most all functions of the body as well as the structural integrity of the cells. The structural integrity of the cell is maintained by the protein component present in the cell membrane. Protein regulates gene – the basic code of life and is present in enzyme – the catalyst used in different chemical activity in the body and hormone – the substances, that control and stimulate organs. Protein is the major components of the disease producing organisms like virus, protective substance like antibodies and treatment medications like antibiotics.
Proteins are very complex nitrogenous organic compounds built up of smaller units called amino acids. There are about 21 amino acids in the body. Most of the amino acids can be synthesised in the body but few can not be synthesised and to be provided in the food. Since it is essential to be provided in food for normal functioning of the body, they are called essential amino acids. There are eight essential amino acids and they are isoleucine, leucine, lysine, methionine, phenylanine, tryptophan, threonine and valine. In infants apart from these amino acids histidine is essential to be provided in food. It is wrong to think that since non-essential amino acids can be synthesised in the body, their inclusion in the diet has no value. Some non-essential amino acids can be synthesised only from other essential amino acids so if they are not supplied in the diet some of the essential amino acids will have to be used for their synthesis.
Functions of dietary protein
Sources of proteinsThere are two sources of proteins
- Animal Sources – eggs, milk, mutton, fish, poultry, liver etc.
- Plant sources – pulses and legumes, cereals, nuts, beans, oilseeds etc.
Class I proteins are derived from animal sources since they contain all essential amino acids needed by the body. Egg protein is considered as the reference protein because of its high biological value and digestibility.
Class II is derived from pulses and legumes, cereals, vegetables, nuts and they do not contain all the essential amino acids they lack in one or more amino acids. Individually they may be lacking in one or more amino acids but combinations make it available of all amino acids. For example cereal and pulse combination is better than consuming only pulse or only cereal.
Important sources of protein per 100 gms
|Food stuff||Protein gms||Food stuff||Protein gms|
|Wheat flour||12.1||Wheat germ||29.2|
|Bengal gram whole||17.1||Green gram dhal||24.5|
|Beef muscle||22.6||Egg hen||13.3|
|Mutton muscle||18.5||Milk buffalo’s||4.3|
* Source: Indian council of medical research 1989.
Recommended Allowances for Indians
The Indian council of medical research has recommended 1 gm of protein per kg body weight for a healthy adult but this varies with different growth periods and physiological stages. 55 to 70gms of protein are required daily for pregnant women in the second half of pregnancy and daily for the period of lactation.
Recommended dietary allowances of Indians *
|Particulars||Protein / day||Particulars||Protein / day|
|Man (60 kg)||60 gm||4- 6 years||31gm|
|Woman (50kg)||55gm||7 – 9 years||41gm|
|Pregnant woman||+ 15gm||Boys 10 – 12 years||53gm|
|Lactation 0- 6 months||+25gm||Girls 10 -12 years||55gm|
|Lactation 6 – 12 months||+18gm||Boys 13 – 15 years||71gm|
|Infants 0 – 6months||2.05/kg||Girls 13- 15 years||67gm|
|Infants 6 – 12 months||1.65/kg||Boys 16 – 18 years||79gm|
|Children 1 – 3 years||23gm||Girls 16 – 18 years||65 gm|
* Source: Indian council of medical research 1989.
Extra protein can be given for the following conditions-
- During childhood.
- In pregnancy and lactation
- Excessive menstruation.
- After a severe accident and major surgical procedure.
- In diseases like tuberculosis.
- Excessive burns.
Digestion of protein
Digestion of protein starts in stomach because of the protein-spitting enzyme. The process is continued to duodenum and small intestine. They are broken down to amino acids and small peptide chains and absorbed. Digestion of protein is impaired when there is deficiency of enzymes or there is anatomical defect in digestive tract.
Protein deficiency (causes)
- Low intake or loss of appetite.
- Poor digestion and absorption.
- Reduced synthesis when the amino acids are not converted to albumin.
- Excessive loss in diseases likes nephrites, cirrhosis of liver with ascites (collection of fluid in abdominal cavity), gastroenteropathy and profuse expectoration in bronchiectasis (localised dilatation of bronchus due to infection) or lung abscess.
Protein deficiency (effects)
- Protein energy malnutrition – kwashiorkor and marasmus.
- Delayed wound and fracture healing.
- Decreased resistance to infection because antibody formation is decreased.
- Sprue syndrome.