Graham Bread - so called after Sylvester Graham, who advocated its use - differs from white wheat bread by containing the outer coatings of the wheat kernel, called bran, which contain a larger percentage of albuminous material and of phosphate. The bran, however, while containing serviceable food products, is so difficult of digestion that it tends to irritate the mucous membrane of the intestine and increase peristaltic action. For this reason it is more laxative than white wheat bread, but also less nutritious.

It is a popular idea that coarse bread, black bread, whole-meal bread, etc., are more nutritious than the bread made from refined white wheaten flour or delicate French breads. This is not necessarily true, and much depends upon the digestive organs of the individual. In a report on the digestibility and nutritive value of bread (Bulletin No. 85, U. S. Department of Agriculture, 1900) by Charles D. Woods and L. H. Merrill, they show the coefficient of digestibility of white bread averages 93.37 per cent (in some samples it is as high as 97.06 per cent), whereas that of whole-wheat bread is 91.50 per cent, and that of Graham bread is but 86.94 per cent. They also found that bread was rendered more digestible when eaten with milk than if eaten alone, the increase in digestibility amounting to 15 per cent. There are peasants in Europe who can thrive upon the coarsest forms of sour, black bread, and there are others who can use different forms of fermenting foods and beverages which to those unaccustomed to them would prove most injurious. Thus generalisations cannot be made, for much depends upon the condition of life of the individual and the general habit of his digestive organs.

Wheat bran contains about 15 per cent of nitrogenous material, 3.5 per cent of fatty matter, and 6 to 7 per cent of mineral substance, mainly phosphates (Yeo), all of which materials, from a purely theoretical standpoint, should be nutritious, but, practically, little bran is absorbed, and it is often irritating, especially where feebleness of the digestive organs exist. As proved by the researches of Professor Snyder, this is the reason why bread made from patent flours is so much more digestible than that made from Graham or whole wheat flour.

According to Bauer, "with wheaten bread, rice, macaroni, etc., the carbohydrates are utilised to within 0.8 or 1.6 per cent, whereas of black bread, potatoes, and the like, 8 to 18 per cent of the carbohydrates are passed with the feces".

Decorticated flour is prepared by special methods of grinding with the object of removing two or three of the outermost and toughest coverings of the grain, but not the inner envelope. Yeo says of bread made from such flour, that while it may be suitable "for young and growing persons with sound and active digestion," it may " prove very indigestible to adults leading sedentary lives. It makes a bread which is usually heavier, moister, and of closer texture than that made from the finest wheat flour".

When digestion is not vigorous, it is better to obtain the necessary nitrogenous material from animal sources. The special uses of coarse forms of bread will be pointed out under the treatment of constipation.

The portion of grain which is useless in the diet of man is wholesome for some of the lower animals, who can convert it into flesh, to be eventually eaten by man.