174 



Every person, however, should have 

 a good general idea of the composition 

 of common foods and of the comparative 

 number of Calories supplied by each. 

 In planning meals for babies and for 

 people who are not well or who are not 

 normal in weight, constant use of the 

 tables is desirable. By doing Exercises 

 4, 5, and 6 you will learn something 

 about planning meals. 



What you should know about proteins. 

 It is generally agreed that a little over 50 

 per cent of the total Calories should come 

 from carbohydrates, about 30 per cent 

 from fat, and not less than 12 per cent 

 from protein. For the average person 

 there should be about 80 grams (3 oz) of 

 protein daily. Much of the protein is 

 used in assimilation. Therefore, during 

 active growth, children often need com- 

 paratively large amounts of protein. 



There is something else you must 

 keep in mind about proteins besides the 

 amount. There are many kinds of pro- 

 teins, those in animal foods being more 

 like your body proteins than are the 

 proteins in plants. You have read that 

 when plants synthesize proteins they first 

 make simpler nitrogen compounds called 

 amino acids. Some twenty-odd amino 

 acids are known to chemists and the com- 

 binations of amino acids in plant foods 

 differ somewhat from those in animal 

 foods. In fact, certain amino acids are 

 completely lacking in most plant foods. 

 This means that most plant proteins do 

 not make adequate substitutes for animal 

 proteins. Wheat contains, among several 

 proteins, only one that is as useful as 

 animal proteins. Legumes (the various 

 beans and peas) contain much protein, 

 and the proteins are very good; this is 



Honjo a Cojnplex Animal Uses Food unit iv 



particularly true of soybeans. But with 

 these exceptions plant foods are not as 

 good sources of proteins as are meat, fish, 

 eggs, milk, and milk products, which are 

 the more expensive foods. 



What you should know about carbohy- 

 drates and fats. You already know that 

 for the most part you depend on carbo- 

 hydrates and fats for your energy. Fats 

 provide more than twice as much energy 

 pound for pound as sugar and starch. 

 However, although fats contain more en- 

 ergy per pound than any other food, it 

 is not wise to eat large amounts of fat. 

 The body does not deal with them as 

 successfully as with other foods. Pro- 

 teins, if they are oxidized, give the same 

 amount of energy as carbohydrates. But 

 to get enough energy from lean meat you 

 would need many pounds daily; and meat 

 is always expensive. All in all, therefore, 

 carbohydrates are our best energy pro- 

 ducing foods. When energy is needed 

 immediately, there is no food as satis- 

 factory as sugar. Lumps of sugar and 

 bars of chocolate are often given to foot- 

 ball players before beginning a game. 

 And you know that, during a war, large 

 amounts of chocolate and other sweets 

 go to the armed forces. Alcohol provides 

 much energy for a short time, but it may 

 also reduce efficiency. 



When carbohydrates and fats are not 

 oxidized they are usually converted into 

 body fat which accumulates under the 

 skin, in the muscles, and next to internal 

 tissues (see Fig. 157). Some fat tissue is 

 necessary to keep us warm, and when a 

 person is unable to eat because of illness 

 or lack of food the fat stored in these 

 tissues is changed back into substances 

 which can be oxidized, providing energy. 



