This section is from the book "Practical Dietetics With Special Reference To Diet In Disease", by William Gilman Thompson. Also available from Amazon: Practical Dietetics with Special Reference to Diet in Disease.
For some flours the whole of the wheat is used, the gluten nitrates and phosphates being all retained. They are more delicate than oatmeal, and more digestible.
Wheat yields soluble matter, such as albumin and dextrin, amounting together to about 10 per cent, besides various salts. The insoluble matter of the grain is chiefly starch and gluten, which constitute from 72 to 75 per cent. Wheaten bread contains about 25 per cent of carbon and 1.2 per cent of nitrogen (or about 8 per cent of protein material). The proportion which these elements bear to each other and which is needed for maintenance of life is carbon fifteen to nitrogen one; hence it appears that wheaten bread alone is not an economical food. If man is to live upon it alone for any length of time, brown bread or Graham bread is better than the varieties made from fine flour, from which latter the nitrogenous elements have been largely removed by milling. A "bread-and-water diet" is proverbially a reducing diet, and as such it is given to insubordinate prisoners (see Diet in Prisons), but they cannot subsist upon it for longer than two or three weeks at most.
Bread made of whole meal is usually not so light as that made with refined white flour. The explanation of this is said to be the fact that the silicious envelope of the grain contains a ferment resembling diastase, which is called cerealin. While the dough is rising, this ferment acts upon a good portion of the starch, forming viscid compounds of dextrin and sugar, which by agglutination prevent the carbonic-acid gas from puffing up the bread as much as it should. On the other hand, too much attrition in the mill ruptures the individual starch granules, and without the use of artificial baking powders the bread will not be light and wholesome. "Seconds" is a medium ground flour which makes a digestible bread.
The British Commissioners of Prisons recommended the use of whole-meal bread for convicts at hard labour on account of its greater cheapness and nutritive value, but advised a modification in the process of its manufacture. The dough is made of flour from which the sharps, etc., have been removed. The latter are then added and mixed thoroughly with the dough just before it is ready for baking, and it is claimed for this process that there is not time for the cerealin to act, and consequently the bread is much lighter.
Pumpernickel is a German black bread made with unbolted meal and sour dough. It is somewhat laxative.
Zwieback is a thoroughly dry form of bread, which is very wholesome for invalids.