Food is any substance which when taken into the body serves to provide materials for liberation of energy, body structure maintenance, repair, growth of tissues, development, reproduction and resistance to diseases. Most of our food elements are complex organic molecules. The major components of food are carbohydrates, proteins, fats, vitamins, minerals and water. The plant cellulose is the principal source of carbohydrates for many herbivorous animals. Man and other animals, subsisting cereal grains, fruits, and tubers, take carbohydrates mainly in the form of starch. Most human beings are omnivorous in diet and take vegetables as well as animal foods in the cooked form.
1. Energy: Components of food function as respiratory substrates (glucose). They liberate energy required by the body to carryout numerous life functions.
2. Growth: Components of digested food build up new protoplasm and new cells for growth.
3. Structure: Components of food get converted into absorbable state during digestion. The same are absorbed and transported to different parts of the body for assimilation. The assimilated materials form various components of the body like bone, skin, muscles etc.
4. Repair: Food provides materials for repair of injured and old tissues.
5. Replacement: A very large number of cells die out daily in the body. They are replaced by newly formed cells. Formation of new cells requires food materials.
6. Formation of hormone and enzymes: Food provides materials for manufacture of regulatory substances like hormones and enzymes.
7. Immunity: Antibodies, antitoxins and some WBC (white blood corpuscles) are involved in maintenance of immune system of the body against attack from pathogens. They are produced from food materials.