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Digestion of Whole Wheat and White Breads in the Human Stomach^*

Department of Vital Economics, University of Rochester, Rochester, New York

Peeled-wheat bread, which is made from flour containing all of the wheat kernel except the outer epidermis weighing less than 2%, has been studied in comparison with several other breads in experiments on gastric digestion in six human subjects. Samples drawn from the stomach by means of the Rehfuss tube 1 hour after eating were analyzed for total and free acidity, total solids, pepsin, total and free reducing substance, and total and soluble nitrogen. Corrections for time lost in sampling and for free reducing substance and soluble nitrogen in the breads made possible the calculation of rates of carbohydrate and protein gastric digestion.

The peeled-wheat bread baked with high-vitamin yeast undergoes gastric proteolytic digestion 15% faster than when the bread is baked with ordinary bakers' yeast; the free sugar formation under the amylolytic action of saliva is 11% faster. Calcium pantothenate in 16 mg. doses taken at least twice before the meal (8 to 10 hours and 1 hour) accelerates the two digestion rates to about the same extent. Pantothenic acid in the test meal of high-vitamin yeast bread exceeded that of the same bread baked with ordinary yeast by only 0.45 mg. If this is the only vitamin B-factor affecting digestion rates, it appears that a relatively small amount in the bread is as effective as a much larger amount taken before the meal.

A "high extraction" white bread containing 3.5% milk solids, based on the flour, and made with high-vitamin yeast, showed a digestion rate for protein and carbohydrate 36% and 3%, respectively, faster than that for the peeled-wheat bread. A white bread made of "straight grade" flour representing an extraction, according to the manufacturer, of "about 72% of the entire wheat berry" and containing 2.5% non-fat milk solids based on the flour showed digestion rates 61% and 11%, respectively, faster than those for the peeled-wheat bread. This white bread, however, was digested only 39% faster than the peeled-wheat bread baked with high-vitamin yeasts with respect to protein, and not at all faster as regards the carbohydrate.

The shortcoming of whole wheat bread does not lie in a lesser peptogenic effect, for the pepsin content in the gastric digests was 40% higher than in those from the white breads.

Manuscript received 18 January 1943.