It is well known that only a portion of the food taken into the
alimentary canal is digested and absorbed into the circulation. It
is obvious that the undigested food plays no part in the process of
metabolism, therefore it is necessary to know the amount of the various
food elements that are digested. For this reason we will notice briefly
the method used in making digestive experiments.
[Sidenote: Determination of the amount of food the body uses]
The food eaten for a certain period of time is analyzed and weighed,
and the intestinal excreta, corresponding to the quantity of food under
study, is also weighed and chemically analyzed. The difference should
show the amount of food actually digested.
There are several serious difficulties in the way of making accurate
digestive experiments:
[Sidenote: Quantity of feces and time consumed in passing food through
the body]
1. It is very difficult to determine the quantity of feces
(intestinal excreta) that corresponds to a given quantity of food.
A digestive experiment is usually conducted for a period of about
one week, the man or animal being given a spoonful of lampblack at
the beginning and at the close of the experiment. The lampblack
being a finely powdered form of pure carbon, is insoluble in the
digestive juices, hence passes through the body without change,
thus blackening or marking the feces at the beginning and at the
end of the test period. The subject under experiment should be
given the same diet for a few days before and after the experiment,
so that the error due to the inability to accurately separate the
feces will be reduced to a minimum.
[Sidenote: Measuring the digestible portion of food]
2. The digestive juices, and especially the bile, pour
considerable material into the alimentary canal which cannot be
distinguished from the undigested elements of food. However, it
is fair to assume that when large quantities of body-proteids
are poured into the alimentary canal, and passed out with the
feces, this amount of matter is wasted by the body, hence should
be charged against the food which stimulated the secretion. For
example: If grain causes a large secretion of digestive enzyms,
it is no more than fair to say that grain is less digestible than
milk, which wastes less body-matter in its digestion.
[Sidenote: Certain foods may either aid or hinder digestion]
[Sidenote: The mono-diet system]
3. A further difficulty with the accuracy of digestive
experiments, and one to which in the past too little attention
has been paid, is the influence upon the digestibility of one
food by the presence of others. Some foods, such as fruits, aid
the digestion of other foods, while in many cases the presence
of a certain article seriously hinders the digestive process of
all. This emphasizes the great necessity for observing the laws
of chemical harmony in combining our food at meals, and it also
emphasizes the importance of limiting the diet to the fewest number
of things possible, which in the opinion of the writer will lead
inevitably to the mono-diet system, especially in curative or
remedial feeding.
[Sidenote: Difficulty of determining amount of undigested food]
From the standpoint of the above difficulties, all digestive experiments
thus far made are only approximately correct, and we are forced back
to the conclusion that if we obey the laws of nutrition, Nature will
give us her highest result expressed in endurance. If a single article
of diet is taken by a man who is accustomed to large quantities of a
highly varied bill of fare, the digestive process will not act in the
usual way. On the other hand, if several articles such as nuts, grains,
and milk are taken at one time, it will be impossible to determine what
percentage of the proteid or of the fat from the three various sources
remains undigested in the intestinal residue, hence no accurate results
can be shown regarding the digestibility of each particular food.