The history of all these investigations cannot be fully explained here, but the discussion must be confined to that which actually takes place in the metabolism of proteids.
Composition of proteids
Proteids, as the student will remember, contain carbon, hydrogen, oxygen, and nitrogen, and sometimes small quantities of sulfur, phosphorus, or iron. These forms of proteids are now known to be chemically changed, by the digestive enzyms of the intestines, into simpler compounds containing these same elements.
How proteids may form body-fats
These simple nitrogenous substances pass into the liver. Just as the liver regulates the supply of blood sugar, so it regulates the supply of nitrogenous compounds in the blood. A certain amount of proteid-forming material is passed through the liver, and goes on to perform the various functions for which proteid is utilized in the body. All nitrogenous material in excess of the amount required by the body is secreted by the liver, and the nitrogen, together with a portion of the carbon, hydrogen, and oxygen, is split off, forming urea, which is excreted by the kidneys. The remainder of the proteid substance, having been robbed of its nitrogen, is now essentially the same as carbohydrates, and goes to form glucose or blood-sugar, which may in turn form body-fats.
Excess of proteids harmful
In the light of this explanation, we can understand several things already mentioned. It has been stated that proteid is the most essential food material of the body because it alone contains the nitrogenous compounds from which the body-tissues, and the chemical enzyms which control all living processes, can be constructed. But we now see that as important as is a supply of proteid materials, any excess above the body-needs is immediately turned into glucose and urea. The glucose, though useful to the body, could be taken in a simpler and less expensive form, while the urea is a waste-product, harmful to life, and must be immediately excreted by the kidneys.
The nitrogen that is actually used in the body serves a different purpose from that which is split off from the excessive proteid taken as food. The food proteid is simply split by the chemical addition of water, much the same as starch and other carbohydrates are changed into glucose. The proteid that is really used by the body is oxidized, and is excreted by the kidneys chiefly in the form of creatinin and uric acid.
FOOD STANDARDS
Incorrect interpretation of scientific data