Food is any material prepared for consumption to supply nutrition to an organism. Generally, food is generally of animal, plant or even fungal source, and has necessary nutrients, like proteins, vitamins, minerals, or carbohydrates. Plants are classified into three types-the vegetal foods, the animal foods and the fruits and vegetables. Animals are classified as fish, mammals, birds and insects, and all other animals. Fruits and vegetables are the commonest of all nourishing materials. Various nourishing principles are applicable in food processing, with respect to the three different classifications.

The first principle that should be followed for ensuring proper nutrition is that food should be bought in sufficient quantities. For instance, in the case of human beings, it should be remembered that even a small quantity of food would have to be consumed in order to maintain a normal life. This principle is applicable also to animals, with the result that, in order to keep their health, a small quantity of food has to be fed occasionally. Thus, it can be concluded that humans should buy food in adequate quantities from markets and farms, so that there is no chance of any deficiency in food. In case of any shortage in food, people should be able to satisfy their basic needs through other sources of food.

Another important rule of nutrition is that the food should be nutritionally balanced, i.e., having appropriate proportions of the required components. In other words, there should not be any deficiency of any constituent of food. One constituent should constitute a considerable part of the food, and another constituent should be derived only from a single source, like fats. In order to maintain the balance in food, it is important to purchase food that comes from reputed suppliers. This will help in ensuring the right balance in nutrition and will also prevent any chances of deficiency of any component in food.