for instance, 1/2 ounce of sugar and 1/2 ounce of butter. As far as the
actual weight of these two foods is concerned, they are equal; but with
regard to the work they do in the body they differ considerably. Their
relative value in the body, however, can be determined if they are
measured by some unit that can be applied to both. It is definitely
known that both of them produce heat when they are oxidized, that is,
when they are combined with oxygen; thus, the logical way of measuring
them is to determine the quantity of heat that will be produced when
they are eaten and united with oxygen, a process that causes the
liberation of heat. The calorie is the unit by which this heat can be
measured, it being the quantity of heat required to raise the
temperature of 1 pint of water 4 degrees Fahrenheit, which is the name
of the thermometer commonly used in the home. When burned as fuel, a
square of butter weighing 1/2 ounce produces enough heat to raise 1 pint
of water 400 degrees Fahrenheit, and it will yield the same amount of
heat when it is eaten and goes through the slow process of oxidation in
the body. On the other hand, 1/2 ounce of sugar upon being oxidized will
produce only enough heat to raise the temperature of 1 pint of water
about 230 degrees Fahrenheit. Thus, as will be seen, 1/2 ounce of butter
has a value of approximately 100 calories, whereas 1/2 ounce of sugar
contains only about 57-1/2 calories.

Other foods yield heat in varying degrees, and their food value is
determined in exactly the same way as that of butter and sugar. To give
an idea of the composition of various food materials, as well as the
number of calories that 1 pound of these food materials will yield, food
charts published by the United States Department of Agriculture are here
presented. As an understanding of these charts will prove extremely
profitable in the selection of food, a careful study of them at this
time is urged. In addition, reference to them should be made from time