. Domestic science, principles and application; a text-book for public schools. Mineral matter, as found in the ash of foods. 5. PFa/^r.—Water is usually not thought of as a food; itis used in tissue building, but it does not give heat or energy. Composition and Functions of the Food Classes.—Proteins contain nitrogen, carbon,oxygen,hydrogen, sul-phur, and often phosphorus. Because they contain nitrogen, proteins build andrepair tissues, and are called nitrogenous or tissue-build-ing foods. The protein of the body, as contained in themuscles, blood, and other tissues, can be built up only from
. Domestic science, principles and application; a text-book for public schools. Mineral matter, as found in the ash of foods. 5. PFa/^r.—Water is usually not thought of as a food; itis used in tissue building, but it does not give heat or energy. Composition and Functions of the Food Classes.—Proteins contain nitrogen, carbon,oxygen,hydrogen, sul-phur, and often phosphorus. Because they contain nitrogen, proteins build andrepair tissues, and are called nitrogenous or tissue-build-ing foods. The protein of the body, as contained in themuscles, blood, and other tissues, can be built up only fromthe protein of food. Proteins may also be used in the bodyto produce heat and energy. But carbohydrates and fats,especially the former, are much cheaper as a source ofheat and energy, and are much more easily used for thispurpose in the body. If less pro>tein is eaten than is re-quired, the protein of the body itself will be more protein is eaten than is needed for tissue building,the excess is thrown off as waste, the process forming 20 DOMESTIC SCIENCE. Fig. 3. Food chart of comparative composition and fuel value offood materials. (U. S. D. A. Bui.) ES8ENTIAL8 TO LIFE 21 harmful products in the body and enforcing greater workon the excretory organs. Excessive consumption of pro-tein food is harmful. Carbohydrate is the general name for a large class offamiliar food materials that do not contain nitrogen. Inorder to maintain its temperature and to do work, thebody must obtain energy, and this is supplied very largelyby the carbohydrates. Starches and sugars are producedin plants on a very generous scale for our use. Wheneaten in excess, carbohydrates are stored in the body asfatty tissue. Fats and oils are composed of the same elements as car-bohydrates; namely, carbon, hydrogen, and oxygen, andare used in the body for the same purpose. The propor-tion of carbon is much greater than in carbohydrates, forwhich reason they give about twice as much heat andener
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