55. The Body as a Machine. Wholesome food and fresh air are necessary for a healthy body. Many housewives, through ignorance, supply to their hard-working husbands and their growing sons and daughters food which satisfies the appetite, but which does not give to the body the elements needed for daily work and growth. Some foods, such as lettuce, cucumbers, and watermelons, make proper and satisfactory changes in diet, but are not strength giving. Other foods, like peas and beans, not only satisfy the appetite, but supply to the body abundant nourishment. Many immigrants live cheaply and well with beans and bread as their main diet.
It is of vital importance that the relative value of different foods as heat producers be known definitely; and just as the yard measures length and the pound measures weight the calorie is used to measure the amount of heat which a food is capable of furnishing to the body. Our bodies are human machines, and, like all other machines, require fuel for their maintenance. The fuel supplied to an engine is not all available for pulling the cars; a large portion of the fuel is lost in smoke, and another portion is wasted as ashes. So it is with the fuel that runs the body. The food we eat is not all available for nourishment, much of it being as useless to us as are smoke and ashes to an engine. The best foods are those which do the most for us with the least possible waste.
FIG. 26.—The bomb calorimeter from which the fuel value of food can be estimated.
56. Fuel Value. By fuel value is meant the capacity foods have for yielding heat to the body. The fuel value of the foods we eat daily is so important a factor in life that physicians, dietitians, nurses, and those having the care of institutional cooking acquaint themselves with the relative fuel values of practically all of the important food substances. The life or death of a patient may be determined by the patient's diet, and the working and earning capacity of a father depends largely upon his prosaic three meals. An ounce of fat, whether it is the fat of meat or the fat of olive oil or the fat of any other food, produces in the body two and a quarter times as much heat as an ounce of starch. Of the vegetables, beans provide the greatest nourishment at the least cost, and to a large extent may be substituted for meat. It is not uncommon to find an outdoor laborer consuming one pound of beans per day, and taking meat only on "high days and holidays."
The fuel value of a food is determined by means of the bomb calorimeter (Fig. 26). The food substance is put into a chamber A and ignited, and the heat of the burning substance raises the temperature of the water in the surrounding vessel. If 1000 grams of water are in the vessel, and the temperature of the water is raised 2° C., the number of calories produced by the substance would be 2000, and the fuel value would be 2000 calories.[A] From this the fuel value of one quart or one pound of the substance can be determined, and the food substance will be said to furnish the body with that number of heat units, providing all of the pound of food were properly digested.
[Footnote A:] As applied to food, the calorie is greater than that used in the ordinary laboratory work, being the amount of heat necessary to raise the temperature of 1000 grams of water 1° C., rather than 1 gram 1° C.]
TABLE SHOWING THE NUMBER OF CALORIES FURNISHED BY
ONE POUND OF VARIOUS FOODS
| FOOD | CALORIES | FOOD | CALORIES |
| Leg of lean mutton | 790 | Carrots | 210 |
| Rib of beef | 1150 | Lettuce | 90 |
| Shad | 380 | Onion | 225 |
| Chicken | 505 | Cucumber | 80 |
| Apples | 290 | Almonds | 3030 |
| Bananas | 460 | Walnuts | 3306 |
| Prunes | 370 | Peanuts | 2560 |
| Watermelons | 140 | Oatmeal | 4673 |
| Lima beans | 570 | Rolled wheat | 4175 |
| Beets | 215 | Macaroni | 1665 |
57. Varied Diet. The human body is a much more varied and complex machine than any ever devised by man; personal peculiarities, as well as fuel values, influence very largely the diet of an individual. Strawberries are excluded from some diets because of a rash which is produced on the skin, pork is excluded from other diets for a like reason; cauliflower is absolutely indigestible to some and is readily digested by others. From practically every diet some foods must be excluded, no matter what the fuel value of the substance may be.