The manner in which scientists measure the fuel value - that is, the amount of heat and energy given off by a certain food when burned in the body - is interesting. Heat can be measured only by a change of temperature, not by weight or length. The heat measure cannot be a pound or a yard; it must be a definite quantity of heat. If a pint of water (or a pound, which is the same thing) is raised four degrees in temperature, say from 40 degrees to 44 degrees, or 70 degrees to 74 degrees, a certain amount of heat is required. This amount of heat is called a calorie; therefore a calorie is simply the amount of heat or energy given off by the body in burning up a certain amount of food.

If one ounce of protein, the fibrin of lean meat, for example, is burned in the body, it will yield a little more than 113 calories of heat. That is, one ounce of protein will give off a little more than 113 times the amount of heat required to raise the temperature of a pint of water four degrees. A pound of protein would equal 1820 calories of energy.

If one ounce of pure sugar is burned in the body, it will yield a little more than 113 calories. One pound of sugar will supply 1820 calories.

If one ounce of fat is burned in the body, the result will be about 255 calories; and one pound of fat will yield 4040 calories.

It will be noted at a glance that the heat value of fat is more than double the heat value of lean meat or sugar, a fact that is proved by daily experience.

Scientists have shown that a man who does average muscular work, a carpenter for instance, requires food sufficient, when burned in his body, to yield about 3400 calories of energy daily to enable him to do his work. Now, seven-eighths of a pound of fat, or two pounds of sugar, or two pounds of lean meat would provide approximately the number of calories required; but it is very evident that either the fat or the sugar would be a very poor ration, for the reason that both foods are practically pure fuel, and would leave nothing for bulk or repair. Work, and even life itself, on such a ration for any length of time would be almost impossible. The lean meat ration would be little better. If, on the other hand, this same amount of energy were derived from a variety of food materials which provide for restoring broken down tissues as well as for energy, the day's work could be performed with ease and efficiency.

Fortunately, nature does not require a scientific knowledge of calories for normal good health; neither does she require that each person consume an exact number in the day's ration, and no more. She is far kinder and more liberal than that. She has provided us with an abundance of foods for body-building, for fuel and energy, for bulk, and for necessary mineral matters. These foods have been carefully studied by scientists and grouped as to their various uses and properties.

What the intelligent cook chiefly needs is a familiarity with these food groups, and a knowledge of what the particular foods of each group may be depended upon to do in the body. She can then plan the family meals so that they will contain the proper amount of material from each group necessary for good health and efficiency. The human body is so adaptable that it is not necessary that each meal should be balanced with scientific accuracy, even if that were possible. If on the whole, from day to day and week to week, the various elements are provided for and eaten, the meals will be sufficiently balanced.