We are dependent on foods for the source of energy that is necessary to perform our work and maintain our body temperature much in the same way that a steam engine is dependent on the fuel supplied it to perform the mechanical tasks assigned to it, and this fuel value of foods in turn, depends on the amount of protein, carbohydrate and fat, particularly the latter, that are present in the foods. At once we see, in our concentrated nuts, a tremendous source of energy, provided that we can digest these nuts and make this energy available.
Despite the fact, as revealed by chemical analysis, that in nuts we have a source of protein and fat in a concentration rarely seen in foods, there have been relatively few experiments to actually determine the digestibility. Prof Jaffa at the California Experiment Station was the first to make a comprehensive investigation along these lines. He made extensive digestion tests on men using most of the more common American nuts. His results, as reported in a bulletin of the U. S. Department of Agriculture, indicated that nuts when they made up a substantial portion of the diet, were well digested by those who ate them and gave no intestinal disturbance or discomfort.
Nuts have had a reputation for indigestibility that was wide spread, not only among people in general, but also among physicians and dieticians, and even Prof Jaffa's clear cut experiments failed to dispell this idea of indigestibility that had been empirically assigned to nuts. A few years ago, a rather extensive series of digestion experiments were inaugurated at Yale University in an effort to settle this question of the indigestibility of nuts and also to test out some of the commercial nut products to find what effect roasting, boiling, and other processes that nuts are subjected to, had to do with the digestibility. Through the courtesy of Dr Kellogg of Battle Creek, it was possible to follow up these experiments with a series here at Battle Creek. It is the result of these tests that I wish to speak of today. One word regarding the method which is the conventional one for such experiments. The amount of food eaten by the individual or animal is weighed at each meal and the composition determined by chemical analysis. The intestinal output is collected, weighed and analysed. From the difference in any substance such as protein in the food and the protein which appears in the body refuse, the amount digested and absorbed or utilized by the body is easily determined. For example; if 10gms. of nitrogen were eaten in the food and one gm appears in the feces, we say that the coefficient of digestibility of that nitrogen is 90%, that is 9 of the 10 gms. eaten were absorbed by the body. The average of a great many such tests on mixed diets has the following standard coefficient: protein 93%, fat 95%, and carbohydrates 98%.