Food is cooked for the following reasons :
Improves digestibility : Hard grains like beans, peas and block grains are cooked to soften them. The digestive juice penetrates easily into the tender and soft grains ensuring total utilisation of proteins and carbohydrates present in them.
Changes taste, flavor and palatability : Cooking changes the taste of food. Fish and meat odours undergo a tremendous improvement in flavor and degree of palatability by cooking.
Increases nutrient availability : Dais, legumes and soyabeans contain trypsin inhibitor. It gets destroyed by dry as well as wet cooking methods thus increasing the nutrient availability,
Makes food safe and increases shelf life : Raw food starts getting spoilt and perishes in due course such as e.g:, tomatoes. If you cook, they will last longer in the form of ketchup or puree. Milk has a tendency to go bad on account of bacteria, which gets killed on boiling and lasts longer as compared to raw milk.
Provides variety : Consumption of food in only one form will make it monotonous. Cooking food in different forms provide variety for e.g., wheat can be eaten in the form of dalia, parantha, chapati etc. It avoids repetition of one form of food.