In addition to the laxative properties of food stuffs, there is another quality of equal importance, which must be duly considered in the treatment of constipation, because of the prolonged stay of undigested food remnants in the alimentray canal in constipation, and of the tendency to delay which will always remain, even under the best conditions which can be supplied. It is of the highest importance that the food should be of such a character as to prevent as far as possible the putrefactive changes which are always increased, and often to an extraordinary degree, whenever there is delay.

Of the three essential food elements, carbohydrates (starch, sugars and organic acids), fats, and proteins, the last named only is capable of undergoing putrefaction. Foods rich in starch and sugar do not undergo putrefaction, either outside the body or within the intestine, and hence, are properly termed atoxic foods.

Fats in excess encourage putrefaction, while starch and sugar in excess produce the opposite effect. By the fermentation of starch and sugar in the intestine, acids are formed, which, as has already been pointed out, by interfering with the growth of putrefactive bacteria, prevent putrefaction. Fats ferment, when taken to excess, forming butyric acid, an irritant poison.

Fruits, starch in vegetables like the potato, and green vegetables of all sorts, which contain little or almost no protein, together with certain sugars, especially milk sugar, maltose or malt sugar, and the sugar of fruits, and to a less degree, cereals, particularly rice, which are very rich in starch, are not only atoxic, being incapable of putrefactive changes, but are also highly antitoxic, since they in a high degree promote the formation of acids in the intestine.