328 HOW DOES MAN DETERMINE THE VALUE OF FOOD? 



the two latter elements in the proportion found in water. Foods 

 rich in carbohydrates are cereals, breads, cakes, fruits, and jellies. 

 Sugars are pure carbohydrates. Fats and oils contain carbon, 

 hydrogen, and oxygen, but their chemical formula shows a rela- 

 tively small proportion of oxygen. Examples of foods containing 

 fats are butter, lard, suet, olive oil, and mayonnaise dressing. 



The fuel value of food. In various experiments it has been 

 agreed that the energy stored in foods as a source of heat should 

 be stated in heat units called Calories. A Calorie is the amount of 

 heat required to raise the temperature of one kilogram of water one 

 degree Centigrade. This is about equivalent to raising the tempera- 

 ture of one pound of water four degrees Fahrenheit. The fuel 

 value of different foods may be computed by burning a given 

 portion of each food in a calorimeter. It has thus been found 

 that a gram of fat will liberate 9.3 Calories of heat, while a gram 

 of carbohydrate or protein will each liberate only about 4 Calo- 

 ries. The burning value of fat is, therefore, over twice that of 

 carbohydrates or proteins. 



Fats and oils have the highest energy value of all foods. But 

 because of their rather indigestible qualities and because one soon 

 tires of an excessive amount of fat, carbohydrates are more used to 

 release energy. Cereals, bread, potatoes, and other starchy vege- 

 tables should, for this reason, be a part of our daily diet. 



Tissue building and repair of waste. But it is not sufficient 

 for man to " count his Calories/ ' We are made of living matter, 

 protoplasm. Living cells may waste away, and need to be repaired 

 or replaced. New cells must be formed. According to Rose 

 it is estimated that the body of a baby at birth contains about 

 4000 Calories of burnable material, while that of a full-grown man 

 averages about 70,000 Calories. Where did this growth come 

 from? Evidently, the tissues use food for building purposes. 



We have already seen that carbohydrates, fats, and proteins 

 all contain the elements carbon, oxygen, and hydrogen, and that 

 proteins alone contain the element nitrogen. We have learned 

 also that the protoplasm, which forms a large part of the body, 

 is thought to be a very complex compound composed of car- 

 Jbon, hydrogen, oxygen, nitrogen, and ten or more other chemical 



