Proteins
Proteins are required for promoting growth and for the building and upkeep of the body tissues. In addition, they are necessary for the production of metabolic and digestive enzymes, blood proteins and hormones. Deficiency of proteins in the diet of adults results in loss of weight, reduced resistance to infection and oedema.
Prolonged differ from one another in their nutritive value and may be broadly classified in to three groups:
1. Complete proteins (proteins of high nutritive value): These proteins can promote good growth in children and young experimental animals e.g. proteins of milk, eggs, meat, fish, liver, etc.
2. Partially complete proteins (proteins of moderate nutritive value): These proteins promote only moderate growth in children or young experimental animals but they can meet the protein requirements of adults e.g., proteins of cereals, millets, pulses, nuts and oilseeds.
3. Incomplete proteins (proteins of very low nutritive value): These proteins cannot promote any growth in young rats nor can meet the protein needs of adults e.g. gelatin.
Fats
Fat along with carbohydrates in the food serves as a source of energy and is also stored in the body beneath the skin. Fat in the diet serves as carrier for the fat soluble vitamins and is also essential for the absorption of carotene (pro-vitamin A.) Fat also supplies the essential fatty acids which are needed by the body. Prolonged deficiency of fat in the diet may causes dryness of the skin.
Carbohydrates:
Carbohydrates serve as the main source of energy to the body. When consumed in excess they are converted into fat and stored in the body. Carbohydrate deficiency in the diet does not occur except in times of food shortage.
Minerals
The minerals present in the diet play an important role in nutrition :
1. As constituents of the mineral matter of the bones ,
2. As structural constituents of the soft tissues and
3. As constituents of physiologically active substances e.g. iron in haemoglobin concerned in regulatory functions.
The more important minerals are calcium, phosphorous and iron.
Calcium and phosphorous: both calcium and phosphorus form the major constituents of bones and teeth and are essential for their formation. Both are present as soluble salts in all the fluids of the body and supply the necessary electrolytes for the action of muscles and nerves. In addition, calcium participates in the coagulation of blood. A deficiency of calcium in the diet causes rickets and decay of the teeth.
Iron: Iron is mainly required for the formation of haemoglobin which is an important constituent of the red blood cells. Prolonged deficiency of iron in the diet causes anaemia.
Vitamins
These are present in very minute amounts in different food-stuffs and are essential for growth and health. The most important of the vitamins are:
Vitamin A and carotene, Vitamin D, Vitamin B1 (thiamine), vitamin B2 (riboflavin), nicotinic acid, vitamin C(ascorbic acid), folic acid and vitamin B12.
Vitamin A and carotene:
Vitamin A is essential for the integrity of epithelial tissues and is a stimulus for new cell growth. It is necessary for maintaining the eye in the healthy condition and for proper vision in dimlight. A continued deficiency of this vitamin in the diet causes night blindness, reduced resistance to infection phrynodrma or toad skin, xerophthalmia(dryness of the conjunctiva of the eyes ), Bilots spots (grayish patches on the white of the eye) and keratomolacia(opacity of the cornea).
Carotene is a precursor of vitamin A and is present in large quantities in green leafy vegetables, tomatoes, carrots and some fruits.
Vitamin D:
Vitamin D increases the absorption of calcium and phosphorous and regulates their concentration in the blood. It directly helps in the formation of hard and healthy bones and teeth. Deficiency of vitamin D causes rickets in children and osteomalacia in adults.
Vitamin B1(thiamine) :
vitamin b1 plays an important part in carbohydrate metabolism . It is essential for the maintaince of good appetite and normal digestion. It is also required for the normal functioning of nerves tissues. A mild deficiency of this vitamin in the diet results in loss of appetite and digestive disturbances. Prolonged deficiency of this vitamin causes the disease known as beri beri.
Nictonic acid(nictin):
Nicotinic acid takes part in the metabolism of carbohydrates, fats and proteins . Severe deficiency of this vitamin causes a disease know as pellagra, characterized by soreness of mouth and tongue , diarrheoa and dark pigementation of exposed parts of the body.
Vitamin C (ascorbic acid): Vitamin C is necessary for the maintaince of good health. It also hastens the healing of wounds and bone fractures. Deficiency of this vitamin in the diet causes the causes the disease scurvy which is characterized by tender, swollen and bleeding gums; bleeding into the skin and joints; anaemia and delayed healing of wounds and bone fractures.
Folic acid:
Folic acid stimulates the formation of red and white blood corpuscles. Deficiency of folic acid in the diet results in the development of macrocytic anaemia. This disease commonly occurs I pregnant and lactating women. Important sources of folic acid are whole cereals, pulses, nuts, green leafy vegetables and liver.
Vitamin B12:
vitamin B12 is identical with anipernicious anaemia factor occurring in liver. It stimulates the formation of red blood cells . Deficiency of this vitamin causes macrocyctic anaemia. This disease commonly occurs in pregnant women subsisting on ill-balance d diets. Vitamin B12 occurs only in foods of animal origin e.g liver, mutton, fish , egg, milk and curds.