expressed in calories, one calory being the amount of heat necessary to raise the temperature of one kilogram of water one degree centigrade. But it is to be observed that this unit is employed simply from convenience, and without implication as to what extent the energy of food is converted into heat in the body. The unit employed in the measurement of some other form of energy might be used instead, as, for example, the foot-ton, which represents the amount of energy necessary to raise one ton through one foot.
Table III.—Estimates of Heats of Combustion and of Fuel Value
of Nutrients in Ordinary Mixed Diet.
| Nutrients. | Heat of Combustion. |
Fuel Value. |
| Calories. | Calories. | |
| One gram of protein | 5·65 | 4·05 |
| One gram of fats | 9·40 | 8·93 |
| One gram of carbohydrates | 4·15 | 4·03 |
The amount of energy which a given quantity of food will produce on complete oxidation outside the body, however, is greater than that which the body will actually derive from it. In the first place, as previously shown, part of the food will not be digested and absorbed. In the second place, the nitrogenous compounds absorbed are not completely oxidized in the body, the residuum being excreted in the urine as urea and other bodies that are capable of further oxidation in the calorimeter. The total heat of combustion of the food eaten must therefore be diminished by the heat of combustion of the oxidizable material rejected by the body, to find what amount of energy is actually available to the organism for the production of work and heat. The amount thus determined is commonly known as the fuel value of food.
Rubner’s[1] commonly quoted estimates for the fuel value of the nutrients of mixed diet are,—for protein and carbohydrates 4·1, and for fats 9·3 calories per gram. According to the method of deduction, however, these factors were more applicable to digested than to total nutrients. Atwater[2] and associates have deduced, from data much more extensive than those available to Rubner, factors for total nutrients somewhat lower than these, as shown in Table III. These estimates seem to represent the best average factors at present available, but are subject to revision as knowledge is extended.
Table IV.—Quantities of Available Nutrients and Energy in Daily Food Consumption of Persons in
Different Circumstances.
| Number of Studies. |
Nutrients and Energy per Man per Day. | ||||
| Protein. | Fat. | Carbo- hydrates. |
Fuel Value. | ||
| Persons with Active Work. | Grams. | Grams. | Grams. | Calories. | |
| English royal engineers | 1 | 132 | 79 | 612 | 3835 |
| Prussian machinists | 1 | 129 | 107 | 657 | 4265 |
| Swedish mechanics | 5 | 174 | 105 | 693 | 4590 |
| Bavarian lumbermen | 3 | 120 | 277 | 702 | 6015 |
| American lumbermen | 5 | 155 | 327 | 804 | 6745 |
| Japanese rice cleaner | 1 | 103 | 11 | 917 | 4415 |
| Japanese jinrikshaw runner | 1 | 137 | 22 | 1010 | 5050 |
| Chinese farm labourers in California | 1 | 132 | 90 | 621 | 3980 |
| American athletes | 19 | 178 | 192 | 525 | 4740 |
| American working-men’s families | 13 | 156 | 226 | 694 | 5650 |
| Persons with Ordinary Work. | |||||
| Bavarian mechanics | 11 | 112 | 32 | 553 | 3060 |
| Bavarian farm labourers | 5 | 126 | 52 | 526 | 3200 |
| Russian peasants | .. | 119 | 31 | 571 | 3155 |
| Prussian prisoners | 1 | 117 | 28 | 620 | 3320 |
| Swedish mechanics | 6 | 123 | 75 | 507 | 3325 |
| American working-men’s families | 69 | 105 | 135 | 426 | 3480 |
| Persons with Light Work. | |||||
| American artisans’ families | 21 | 93 | 107 | 358 | 2880 |
| English tailors (prisoners) | 1 | 121 | 37 | 509 | 2970 |
| German shoemakers | 1 | 99 | 73 | 367 | 2629 |
| Japanese prisoners | 1 | 43 | 6 | 444 | 2110 |
| Professional and Business Men. | |||||
| Japanese professional men | 13 | 75 | 15 | 408 | 2190 |
| Japanese students | 8 | 85 | 18 | 537 | 2800 |
| Japanese military cadets | 11 | 98 | 20 | 611 | 3185 |
| German physicians | 2 | 121 | 90 | 317 | 2685 |
| Swedish medical students | 5 | 117 | 108 | 291 | 2725 |
| Danish physicians | 1 | 124 | 133 | 242 | 2790 |
| American professional and business men and students | 51 | 98 | 125 | 411 | 3285 |
| Persons with Little or no Exercise. | |||||
| Prussian prisoners | 2 | 90 | 27 | 427 | 2400 |
| Japanese prisoners | 1 | 36 | 6 | 360 | 1725 |
| Inmates of home for aged—Germany | 1 | 85 | 43 | 322 | 2097 |
| Inmates of hospitals for insane—America | 49 | 80 | 86 | 353 | 2590 |
| Persons in Destitute Circumstances. | |||||
| Prussian working people | 13 | 63 | 43 | 372 | 2215 |
| Italian mechanics | 5 | 70 | 36 | 384 | 2225 |
| American working-men’s families | 11 | 69 | 75 | 263 | 2085 |
