estion experiments with these flours the
proportions of digestible or available protein and available energy
in the patent flour were larger than in either the entire wheat or
the graham flour. The lower digestibility of the protein of the
latter is due to the fact that in both these flours a considerable
portion of this constituent is contained in the coarser particles
(bran), and so resists the action of the digestive juices and
escapes digestion. Thus while there actually may be more protein in
a given amount of graham or entire wheat flour than in the same
weight of patent flour from the same wheat, the body obtains less
of the protein and energy from the coarse flour than it does from
the fine, because, although the including of the bran and germ
increases the percentage of protein, it decreases its
digestibility. By digestibility is meant the difference between the
amounts of the several nutrients consumed and the amount excreted
in the feces.

"The digestibility of first and second patent flours was not
appreciably different from that of standard patent flour. The
degree of digestibility of all these flours is high, due largely to
their mechanical condition; that is, to the fact that they are
finely ground."--SNYDER.[62]

For a more extended discussion of the subject, the student is referred
to Bulletins 67, 101, and 126, Office of Experiment Stations, United
States Department of Agriculture.

191. Mineral Content of White Bread.--Average flour contains from 0.4
to 0.5 of 1 per cent of ash or mineral matter, the larger portion being
lime and magnesia and phosphate of potassium. It is argued by some that
graham and entire wheat flours should be used liberally because of their
larger mineral content and their greater richness in phosphates. In a
mixed dietary, however, in which bread forms an essential part, there is
always an excess of phosphates, and there is nothing to be gained by
increasing the amount, as it only requires additional work of the
kidneys for its removal. Few experiments have been made to determine the
phosphorus requirements of the human body, but these indicate that it is
unnecessary to increase the phosphate content of a mixed diet. It is
estimated that less than two grams per day of phosphates are required to
meet all of the needs of the body, and in an average mixed ration there
are present