Before looking into the composition of food, it is well to understand just what is meant by the term "food." In order to be a "food" a substance must be fitted to serve a definite function in the body. The body must be fed in order to live. This living process is twofold, as we will see later. One half is the generating of the power to perform daily duties -walking, eating, breathing - and the keeping of the body warm; the other is the constant adding to the body structure which is called growth or repair of tissue. Hence our definition for "food" is any substance which when taken into the body will either produce heat and energy or build tissue.

Every substance can be taken apart by a chemist in his laboratory in order to show of what it is made. If the parts still maintain the characteristic properties of the whole, no matter into how small particles it may be subdivided, that substance is called an element. For instance, a wedding-ring may be broken up and subdivided into particles so small they could only be seen under the microscope, and still each particle would show all the properties of gold. Gold is an element. So also are silver, lead, iron, zinc, copper, and other sub-stances, both solid and gaseous, to a limited extent, which in combination or singly make all matter as we see it around us.

What is a "food"