THE GENERAL NATURE OF DIET 143 



ponents had combustion-values about as given below. These deter- 

 minations approximately are in general use for the calculation of diets. 



COMBUSTION-EQUIVALENTS (PER GRAM). 



Average proteid 4.1 calories. 



Average fat .9.3 calories. 



Average carbohydrate 4.1 calories. 



It is useful to know, as a basis of comparison, that the combustion- 

 equivalent of 1 gm. of hydrogen is 34.622, and of carbon 8.08. In order 

 now to find the approximate energy-value of any given mass of a man's 

 food it is necessary to know only the percentage-proportion of average 

 proteid, fat, and carbohydrate in it. We do not at present know enough 

 quantitatively about the katabolism of the inorganic salts and the water 

 to calculate or allow for them, while comparatively few foods contain 

 albuminoids in important amount. Having learned from one of the 

 standard tables (for example those of the U. S. Agricultural Department) 

 the percentages of fat, proteid, and carbohydrate present, it is necessary, 

 in order to estimate the energy- value of the composite food, only to mul- 

 tiply each component by its combustion-equivalent and add the products. 

 This will give the number of energy-calories in 100 gm. of the food, 

 disregarding salts, water, and albuminoid if present. As an illustration, 

 take a kilo (two-pound) loaf of white wheat bread : what is its value to a 

 hunter, for example, as nutriment? In every 100 gm. of the bread 

 there are about 8 gm. of average proteid, 49.2 gm. of carbohydrate, 

 and only 1.5 gm. of fat (hence people "naturally" eat butter with bread). 

 The salts and water as energizers we disregard. The combustion- 

 equivalent of average proteid is, from Rubner's table above, 4.1 of 

 carbohydrate 4.1, and of fat 9.3. 



8.0 multiplied by 4.1 equals . . . . 32.80 



49.2 " " 4.1 " , 201.72 



1.5 " "9.3 " 13.95 



The products' sum equals . . . 248.47 



In every 100 gm. then of the bread-sample there are probably avail- 

 able for the eater's warmth and strength and tissue-repair 248.47 

 calories of energy. Reduced to heat, this is enough to raise 248.47 

 liters of water 1 C. in temperature. In the supposed kilo-loaf there 

 are ten times as many calories, or a total of 2484.70 calories, or about 

 two-thirds the "fuel," which a very active hunter would require in 

 winter for his personal "engine." If the man eats 100 gm. of butter 

 with this loaf of bread he increases his food materially, and both in a 

 pleasant and an easily available way. A dekagram of butter properly 

 made consists of 0.3 gm. of proteid, 91 gm. of fat, besides water and 

 salts, but no carbohydrate. From the 0.3 gm. of proteid (0.3 X 4.1) 

 would come 1.23 calories of energy, and from the 91 gm. of fat 



