122. Influence Of Food On Secretions

The more recent investigations reveal the fact that the kind of food has an influence not only on the abundance, but on the kind of digestive secretions, which is important, because an abundant supply of digestive juices is necessary to good digestion. The conclusion is, or better perhaps the theory, that certain chemical excitants are conveyed to the secreting glands through the blood circulation, and excite the flow of the several digestive fluids, and that the formation of these excitants is caused by the reaction of food compounds on the inner membranes of the stomach and intestines, this reaction being more pronounced with some food materials than with others. Broths, meat extracts, milk, dextrin, maltose, and dextrose exert a pronounced influence in this way in the stomach, which makes rational the taking of soups or bouillon as the first dinner course, or the eating of toasted bread and zwieback by persons with weak digestion. On the other hand, fats tend to inhibit gastric secretion, so that an excessive proportion of fat in the meat might weaken digestion in the stomach.

Food may exert an indirect influence on the pancreatic secretion. The acid in the chyme stimulates the flow of the pancreatic juice. Any diet, therefore, that has the effect of diminishing or of neutralizing the stomach acid which otherwise would reach the small intestine is unfavorable to pancreatic digestion. Mendel1 states that "the activity of the enzyms of the pancreatic juice seems to be correlated in a marvelous way with the corresponding elements of the diet. A regimen rich in fat calls forth a secretion containing a relative abundance of the lipolytic (fat-splitting) enzyme; with a meat diet, the proteolytic enzymes preponderate, and so forth. Furthermore, this regulative action can apparently be modified by the conditions of the diet. One is almost inclined to speak of a physiologic education of the digestive glands, and to conceive of them as being trained for fat, or proteid, or carbohydrate digestion powers by the presence of the corresponding compounds in the alimentary canal. Indeed, this conception has already been raised above the realm of mere fancy." Such facts as these are significant, and we may reasonably hope that some time in the future bad digestion and the habit of constipation may be relieved through the diet, rather than through medicines.

1 "Some Aspects of the Newer Physiology of the Gastrointestinal Canal," p. 6.

123. Mechanical Condition Of Ingested Food

It is generally held that thorough mastication of food promotes good digestion. This is rational; although involving chemical changes, digestion is broadly considered a means of rendering the nutrients soluble, that is, transferable through the walls of the alimentary canal. The doctrine has been taught, in one notable instance at least, that excessive mastication greatly increases the efficiency of the food. If this is true, it must be because of increased thoroughness of digestion. Observation does not show this result. It is concluded from experimental evidence "that any dietetic practice, therefore, such as excessive mastication, which may be claimed to result in greater economy in the utilization of food so far as it relates to thoroughness of digestion, must improve upon a condition in which there is already almost complete utilization." While in a normal subject, careful mastication may not increase the proportion of nutrients that will ultimately be digested and absorbed, fineness of division of the food particles makes for promptness, and therefore comfort, of digestion, because the larger the food surface which the digestive fluids may attack, the more rapidly will solution be effected, which is highly desirable. Of course bolting the food in coarse pieces may result not only in incomplete, but uncomfortable, digestion. In comparing the digestibility of breads from different kinds of flour, that from coarse flour, that is, whole wheat flour, is found to be less completely digested than bread from fine flour, but this is due, not so much to the degree of fineness as to the presence in the coarse flour of more cellulose (crude fiber) which serves to protect the other constituents of the flour from the action of the various juices.