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A Talk on Food: Body

Air is composed of two invisible gases, oxygen and nitrogen; when carbon is ignited, the oxygen from the air unites with it rapidly, giving off light and heat, and we have what is called combustion, burning or a fire. CARBON DIOXIDE A PRODUCT OF COMBUSTION BOTH OUTSIDE OF THE BODY AND IN IT Pour a little lime-water into a glass jar, shake the jar and note there is no change in the appearance of the lime-water. Pour out the lime-water, rinse the jar, dry it and set into it a lighted candle, cover the top of the jar with a pane of glass and note what happens. The candle burns for a few moments, then, when there is no more oxygen to unite with the carbon of the candle, combustion ceases. Remove the candle, pour in a little lime-water and shake the jar-the lime-water become cloudy. Now put a glass tube into a bottle containing lime-water, letting one opening come below the water, put the other end of the tube into the mouth and exhale from the lungs, letting the air pass into the tube; now shake the jar and note that the lime-water becomes cloudy. When lime-water takes on a cloudy appearance, we know that it contains carbon dioxide. Carbon dioxide is a product of combustion. The carbon dioxide exhaled from the lungs was formed in the body. Oxygen taken in through the lungs unites with the carbon in the food, thus producing carbon dioxide and, incidentally, heat to warm the body. The process of combustion in this case is, probably, almost synonymous with the process of digestion. Thus the process of digestion, or we might say of living, is largely dependent upon our breathing in a full supply of air, pregnant with oxygen. NITROGEN, ITS ABUNDANCE IN THE BODY AND SOURCE OF SUPPLY Nitrogen is the other element of which air is composed. Every active tissue in plant and animal contains nitrogen. Brain, muscle, bone, even the digestive juices and other bodily secretions are all largely made up of nitrogen. If nitrogen be withheld from the body dies, though for a time the vital organs will draw upon the nitrogen stored in the various tissues of the system and the body will carry on its work by feeding upon itself. But it is impossible for the body to take its supply of nitrogen, first hand, as it were, from the air, and though air is four-fifths nitrogen, all of this element is returned to the air, when the oxygen in composition has been taken in by the lungs. Nitrogen must be supplied in composition with other elements in food. The articles we use as food are complex in their composition. ELEMENTS FOUND IN OUR FOOD Our food, then, must contain the elements that make up the body; it must contain carbon, oxygen, nitrogen, hydrogen, iron, sulphur, and all the minor elements that go to make up the body; these exist in articles of food not as simple elements but as compounds, to which, partly on account of their repetition in this and that article of food, we give the name of proximate food compounds or principles.

PROXIMATE OR FOOD PRINCIPLES The chief of these proximate principles are classified as water, mineral matter, proteids, fats and carbohydrates. The body of a man of average weight is said to contain 108 pounds of water, 11 pounds of mineral matter, 29.75 pounds of proteid, 5 pounds of fat and .25 of a pound of carbohydrates. From this we can judge somewhat of the quantity of the different principles to be supplied in the food; but, as we shall see later on, the proportion of the different principles needed depends on still other conditions than the quantity in the body.

The most important of these principles are the proteids, because they are the only ones that can supply the nitrogen so needful in tissue building and repairing; proteid may also furnish heat and energy, but proteid is represented chiefly in our most expensive foods; and, as fats and carbohydrates are less expensive and even better than proteid as a source of heat and energy, it were the part of wisdom to reserve proteid food to build tissue and choose fats and carbohydrates to supply the body with its heat and energy. Indeed, foods abounding in these two latter principles are often called proteid sparers and, also, fuel foods. Thus, if the carbohydrates are to act as fuel foods, furnishing us with heat and energy, we can see that we must supply them in the food in greater proportion than would be indicated by the quantity present in the body as shown above.