FOODS AND DIETARIES 277 



refuse are bones in meat, shells of eggs or of shellfish, the covering 

 of plant cells which form the skins of potatoes or other vegetables. 

 The amount of refuse present also plays an important part in the 

 values of foods for the table. The table ^ on page 276 gives the per- 

 centages of organic nutrients, water, and refuse present in some 

 common foods. 



Fuel Values of Nutrients. — In experiments performed by 

 Professor Atwater and others, and in the appended tables, the 

 value of food as a source of energy is stated in heat units called 

 Calories. A Calorie is the amount of heat required to raise the tem- 

 perature of one kilogram of water from zero to one degree Centigrade. 

 This is about equivalent to raising one pound four degrees Fahren- 

 heit. The fuel value of different foods may be computed in a 

 definite manner. This is done by burning a given portion of a 

 food (say one gram) in the apparatus known as a calorimeter. 

 By this means may be determined the number of degrees the 

 temperature of a given amount of water is raised during the process 

 of burning. It has thus been found that a gram of fat will liber- 

 ate 9.3 Calories of heat, while a gram of starch or sugar only about 

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

 of carbohydrates. In a similar manner protein has been shown to 

 have about the same fuel value as carbohvdrates, i.e. 4 Calories 

 to a gram.^ 



The Relation of Work to Diet. — It has been shown experimen- 

 tally that a man doing hard, muscular work needs more food 

 than a person doing light work. The mere exercise gives the 

 individual a hearty appetite ; he eats more and needs more of 

 all kinds of food than a man or boy doing light work. Especially 

 is it true that the person of sedentary habits, who does brain work, 

 should be careful to eat less food and food that will digest easily. 

 His protein food should also be reduced. Rich or hearty foods 

 may be left for the man w^ho is doing hard manual labor out 

 of doors, for any extra work put on the digestive organs takes 

 away just so much from the ability of the brain to do its 

 work. 



1 W. O. Atwater, Principles of Nutrition and Nutritive Value of Food, U.S. De- 

 partment of Agriculture, 1902. 



