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.