PROBLEM 1 Hoxv Can We Choose Foods Wisely? 



TTie food of living things. You learned 

 earlier that all living things are made of 

 protoplasm and that all need the same 

 compounds, namely, proteins, fats, car- 

 bohydrates, mineral matter, and water. 

 The vitamins that you will read about 

 later are also needed. Carbohydrates are 

 oxidized and release energy. Fats and 

 more rarely proteins are used for oxida- 

 tion too. Proteins, the only food com- 

 pounds containing nitrogen, are always 

 needed for building up new protoplasm 

 by assimilation. 



The source of man's foods. You have 

 read, too, that green plants provide the 

 necessary food for all animals; that the 

 chlorophyll manufactures sugar (photo- 

 synthesis); that the sugar may be con- 

 verted to starch, or to fats; and that the 

 sugar may combine with minerals in the 

 plant in making proteins. Animals get 

 all their food from plants, either directly 

 or indirectly. Either they eat plants or 

 they eat animals which had eaten plants. 

 Thus all animals, including man, are de- 

 pendent on green plants for the com- 

 pounds used in assimilation and oxidation 

 and thus for the energy to live. 



Two meanings of "food." We eat beef- 

 steak, potatoes, vegetable soup, and hun- 

 dreds of other substances. These are the 

 things we think of as our "foods." Each 

 food has a slightly different make-up and 

 a different taste from every other food. 



Yet, in all our foods we get the same 

 kinds of compounds over and over again. 

 They are proteins, sugars, starches, fats, 

 minerals, water, and vitamins. These 

 compounds in their soluble form enter 

 the cells where they keep the protoplasm 

 alive. They are the real food of the plant 

 and the animal. You see, therefore, the 

 word "food" means one thing to the 

 restaurant keeper, the butcher, and the 

 housewife. It means something different 

 in the laboratory and in the classroom. 

 When we think in terms of billions of 

 cells of the body, the word "food" means 

 the essential compounds which make up 

 the beefsteak, potatoes, and other things 

 served to us at the table. In some books 

 the word "nutrient" is used as a name 

 for these compounds used by the cell. 



Why is it helpful to make a study of 

 common foods? Throughout the world 

 people eat the foods they are accustomed 

 to eat because of family habit, or they 

 choose foods that are easy to get or that 

 they like. Sometimes they eat certain 

 foods as a fad or because they think the 

 foods have some special value. This was 

 particularly true before there was a 

 scientific study of diet and it is still true 

 of large numbers of people. Since most 

 people appear to be healthy, the diets 

 they follow must be satisfactory in the 

 main. But a great many people are really 

 not as healthy as they could be if they 



