Ditions from the fuel and water (and air) which it consumes, so the living body derives its energy from the food, water and air upon which it subsists.

Definition Of Food

Poods are substances which when taken into the body supply the necessary elements for promoting its growth and repairing its waste; and furnish it with material from which to produce heat and internal or external work. Substances that are unable to assist in either of these ways are called food accessories or food adjuncts.

Food Accessories Or Food Adjuncts

These are substances which, although unable to fulfill the definition of foods, find an extensive use in the dietary, for a variety of reasons. They give flavor to food, increase the appetite, stimulate secretion, and thus aid the digestive functions. They comprise two classes, viz., condiments and beverages.

Source Of Food

Food occurs in the mineral, plant and animal kingdoms. It occurs in all physical forms of matter - gases, liquids and solids. Gases are mentioned because oxygen is a true food and metabolized to a certain degree, being always present in the blood and tissues in loose chemical combination.

Composition Of The Body

The human body contains many chemical elements in varying amounts.

Nitrogen, carbon, hydrogen, and oxygen are the four present in largest proportion; iron, phosphorus, calcium, magnesium, potassium, sodium, sulphur, chlorin, iodin, also have important offices to perform.

Composition Of Food

Poods must contain the same elements found in the body; thus it is that they are able to build and maintain the body structure. But no "one food" contains all these elements in proper proportions for all persons; therefore, it is by combinations of the various food stuffs that we produce a suitable diet. These elements must further be supplied in forms which the body can use. It cannot utilize carbon in the form of coal, for example, but must have it combined in special ways with hydrogen and oxygen. These combinations of elements or "Pood Compounds" found in nature (sometimes called "alimentary" or "food principles" and "food stuffs"), are usually classified as proteins, fats, carbohydrates, mineral matter (or salts) and water.

Food, as it is taken into the body still differs in composition from the material utilized by the tissues in growth, repair of waste, and production of energy in the form of work or heat. It must be finally prepared for the use of the body by the processes involved in Digestion.