1. Carbohydrates: Sugar, honey, starch, potatoes, rice, wheat, etc., are carbohydrates. They are compounds of carbon, hydrogen, oxygen, sugar, starch, etc. They provide about half of the required energy and thus maintain the temperature of the body. Energy is produced by the burning of sugar.

2. Proteins: Eggs, beans, pulses, fish, etc., are proteins. These are compounds having an excess of nitrogen with carbon, hydrogen, oxygen and sometimes sulphur and phosphorus. They are mainly responsible for growth. Eggs, meat, pulses, etc., are the richest source of proteins. Their absence causes •extreme weakness.

3. Fats and Oils: Oils, nuts, ghee, butter, etc. They contain same components as carbohydrates and are better sources of energy which is again produced by burning. Their deficiency in the body causes several diseases while excess is stored beneath the skin.

4. Vitamins: Every food almost contains some vitamins. They are organic substances which are essential for the growth of the body and are required in small amounts. Their deficiency causes sickness and stunted growth. Each of them performs definite functions as follows :

(a) Vitamin A is present in cod, halibut, shark liver oils, eggs, green vegetables, etc. It is essential for growth of the body and protects skin and other delicate parts of the body. It prevents infection and keeps the eyes healthy. Its deficiency causes night blindness and stunted growth of the body.

(b) Vitamin Bt complex is found in yeast, green vegetables, cereals, etc. Its deficiency leads to beriberi and anaemia.

(c) Vitamin B2 complex is the mixture of about twelve components. It is present in milk, butter, cereals, vegetables, etc. This is very important for growth and blood. The deficiency of this complex leads to subnormal growth, pellagra, etc.

(d) Vitamin C is present in large quantities in vegetables, fresh fruits, orange, etc. Human milk is also a good source of vitamin C. Its deficiency causes scurvy, anaemia, impaired growth, haemorrhage and susceptibility to infection.

(e) Vitamin D is present in cod, shark liver oil, milk, butter, etc. Its deficiency causes rickets in children and osteomalacia in adult females.

(f) Vitamin E is found in cereals, green vegetables, eggs, etc. Deficiency of this vitamin causes sterility.

(g) Vitamin K is mainly confined to green vegetables. This vitamin maintains normal clotting of blood.

(h) Vitamin P is present in association with vitamin C and its functions are closely associated with the same vitamin. It helps the action of vitamin C and keeps the blood capillary healthy.

5. Inorganic Salts: Vegetables, fruits, etc. Salts of calcium, potassium, magnesium, iron, sulphur, iodine, etc., are essential for the health of the body.

6. Water: Most of the food contains water. Water constitutes 75 per cent of our body. It helps the digestion and absorption of food. It also maintains the temperature of body and removes waste products.