In the absence of butter some other form of fat is desirable in the diet, because fat is so concentrated a food. There is a limit to the capacity of the human stomach to hold food. People who live on a diet largely of rice, which has almost no fat in its make-up, develop characteristically distended abdomens, because they have to eat such a great quantity of food to get fuel enough for their day's work. When people are for any reason put on a milk diet for a considerable time it is customary to put something into the milk to make it more concentrated, for otherwise they would drink and drink and then hardly get fuel enough. To give a concrete illustration--a man's energy requirement for a day may be met by from four to five quarts of milk (unless he is doing very heavy manual labor), but it would be much more practical to substitute a loaf of bread, which is comparatively dry, for one quart of milk, and three ounces of fat (six tablespoonfuls) for another quart of milk, making the total volume but little over half what it would be if four quarts of milk were taken. For people who are engaged in hard physical toil, fat is exceedingly important for this purpose of gaining in concentration. "Fat is fuel for fighters," and it is perfectly reasonable to ask those who are not doing much heavy labor to eat other kinds of food and save fat for those who simply have to have it to do their work well. In the ordinary mixed diet one can easily dispense with an ounce of fat (two tablespoonfuls). Each tablespoonful is equalled in energy by an apple, or a banana, a large egg, two half-inch slices of bread about three inches square, four dates, four prunes--and it is no great strain on one's capacity for food to substitute such items for the fat.
On account of its concentration, fat is good for transportation; and aside from its energy value it gives the diet "staying" qualities. Other things being equal, one feels hungry sooner after a meal without fat than after one in which it is liberally supplied. People doing manual labor, and especially out of doors, feel the pangs of hunger more than sedentary folks and hence need more fat to keep them comfortable. No man can do his best work when all the time thinking how hungry he is. It behooves us all then, as good citizens, to recognize the greater need of our soldiers and sailors and our hard-working laborers for as liberal allowances of fat as we can make. At the same time, we cannot for our own best health dispense with fat altogether. We may consider anything up to two ounces apiece a day legitimate for our own maintenance of efficiency.