The Vegetarian Diet


It has been pointed out in the preceding chapters
that it is not possible to make a diet derived entirely
from seeds or seed products, which will adequately
nourish an animal during growth, and it may be
added that such diets will not even maintain a fully
grown animal in a state of health and normal physi-
ological activity over a long period. Without an
appropriate supplementing of seed mixtures with
the elements, calcium, sodium and chlorine, no ap-
preciable amount of growth has been secured with
seed mixtures, in our extensive experience. It was
further pointed out that the leaf is a very different
thing from the seed, tuber or root, from the dietary
standpoint, and these differences in nutritive prop-
erties can be correlated with differences in function.
The seed is a storage organ of the plant, and is filled
with a reserve supply of proteins, carbohydrates, fats
and mineral salts. It is in great measure non-living
matter, and indeed much of the contents of the seed
was never a part of living matter, but only the prod-
uct of it. In the leaf of the plant we have a tissue
which, during life, was very active in the manifesta-
tions of the properties of living matter. With these



differences in function, it was pointed out, there are
found corresponding differences in the dietary values
of the two types of foods, the latter being much more
nearly complete foods chemically, than are the seeds,
tubers and roots.

Let us consider briefly the bearing of these obser-
vations on the whole subject of human and animal
nutrition. It has been pointed out that for many
years the protein and energy value and its digest-
ibility were assumed to determine the value of a
food. The chemist is able to determine approxi-
mately the amount of protein or rather its content
of nitrogen which is taken as a measure of the amount
of protein and the fuel value of a food, and by means
of experiments on animals, the extent to which a
given food is digested and absorbed. He can even
tell by a study of the relation between the amounts
of oxygen absorbed by the tissues, and the amount
of carbon dioxide given off whether the animal is
burning sugar or fat in order to obtain its energy.
The nitrogen eliminated in the urine serves as a meas-
ure of the destruction of protein in the body. With-
out in the least attempting disparagement of the
value of the services of the chemist in the study of
the problems of nutrition, it may truthfully be
said that both his ordinary and his unusual and
most searching methods for the analysis of food-
stuffs fail to throw any great amount of light on
the value of a food or mixture of foods for induc-
ing growth.


In addition to the cereal grains, wheat, oat, maize,
rye, barley and rice, the products of the vegetable
garden which supplied leafy vegetables, cabbage,
lettuce, spinach, cauliflower, brussels sprouts, chard,
celery, various "greens," etc.; roots, such as the
radish, turnip and beet; tubers, such as the potato
and sweet potato, we have had available as food an
abundance of meats and of dairy products. It is
not strange that with such a supply of foods it should
have been taken for granted that any diet consisting
of wholesome foods, combined in such proportions
and taken in such quantities as would furnish
the amounts of protein and energy which exper-
iments on man and animals had shown to be neces-
sary under specified conditions of living, whether at
rest or at work, should prove satisfactory for the
maintenance of health in the adult and of normal
growth in the young. An appreciation of the funda-
mental importance of employing proper combinations
of foods, was impossible, until the systematic efforts
described in the first two chapters, were made to
simplify the diet as far as possible, and to derive it
from restricted sources. These studies have, when
the results were applied to the interpretation of the
quality of the diets of man in several parts of the
world, revealed the fact that man is frequently
failing to make the wisest selection of food. Health
and efficiency can be greatly improved by applying
the knowledge which we now possess concerning
the special properties of several classes of foods, to


the selection of the articles which shall make up the
daily diet.

The biological method for the analysis of single
food-stuffs and mixtures of food-stuffs has made it
evident that the older practice of regarding protein,
energy and digestibility as the criteria of the value of
a food mixture, must be replaced by a new method of
presentation of the subject based upon a biological
classification of the food-stuffs, the latter having its
foundation in the function of the substance employed
in the diet. Such a method of presentation of the
subject of food values offers convincing evidence of
the necessity, for the proper selection of food, that
dietary reforms are greatly needed in many parts of
the world.

There has been much discussion of the relative
merits of the vegetarian diet for man as compared
with diets largely derived from vegetable foods but
more or less liberally supplemented with foods of
animal origin. This question has been discussed
principally from the point of view of the supposed
detrimental effects of a diet containing a high protein
content, and the supposed beneficial effects of a
sparing consumption of protein, and from the point
of view that there are sound ethical reasons why
man should abstain from the use of animal foods.
The adherents of the latter extreme view have never
become numerous, partly because the average in-
dividual has not the self-control to enable him to
forego the use of meats, milk and eggs, on account


of their appetizing qualities, and partly because the
chances of one's succeeding in the selection of a
strictly vegetarian diet which would maintain such
a state of physiological well-being as would make
possible the continuation of his line are very small.
Concerning the ethical considerations involved in
the eating of animal foods, nothing need be said here.
The relative merits of the vegetarian as compared
with the mixed diet, and the evidence regarding the
desirability of taking a low or high protein intake,
may next receive our attention.

The most elaborate attempt to test the relative
merits of the strictly vegetarian diet as contrasted
with the omnivorous type, was made by Slonaker. 1
He fed a group of young rats on a list of 23 vegetable
foods, allowing them free choice within limits. For
comparison, a similar group were fed the same foods
of vegetable origin, but in addition animal food was
given in moderate quantities. Since several natural
foods, raw or prepared, were offered at a time, and
the animals were allowed free choice as to what they
should eat, and since no effort was made to keep
track of the food consumption, or the relative
amounts of the different foods eaten, the results
cannot be employed for critical examination except
in a limited way. The results are of the greatest
interest in showing how far instinct fails to guide
an animal in the selection of its food. Slonaker's
list of foods included nearly everything which a
vegetarian in southern Califorjiia would be likely


to have on his table during the year, and included
seeds, the milling products of seeds and leafy veg-
etables, tubers and roots.

The vegetarian group grew fairly well for a time,
but became stunted when they reached a weight of
about 60 per cent of the normal adult size. They
never increased in size beyond this point. The
omnivorous controls grew steadily to what may be
regarded as the normal size for the adult. The
vegetarians lived, on an average for the entire group,
555 days, whereas the omnivora had an average span
of life of 1020 days. The vegetarian rats grew to be
approximately half as large, and lived half as long
as did their fellows which received animal food.
Slonaker drew the conclusion that a strictly veg-
etarian diet is not suitable for the nourishment of an
omnivorous animal, but was unable to say why this
should be true.

The results of Slonaker were published in 1912,
and just at the time when McCollum and Davis were
securing the experimental data which revealed the
differences in the growth-promoting power of fats
from different sources and which established the
fact that a hitherto unsuspected dietary essential
existed. They fed their diet of relatively pure food-
stuffs described on page 16 with various fats of both
animal and vegetable origin and found that no fat
which was derived from plant tissues came in the
growth-promoting class along with butter fat, the
fats of egg yolk, and of the glandular organs. It


seemed to McCollum and Davis that the most
probable explanation of the results of Slonaker was
the absence or shortage in his vegetarian diet of the
dietary essential which is furnished so abundantly
by butter fat, and which later came to be designated
as fat-soluble A and to a low protein intake. With
this idea in mind they tried during the summer of
1914 an experiment similar to that of Slonaker's, but
modified so as to give the animals a much higher
protein content than his rats probably took. It
seemed that if Slonaker's vegetarian rats ate liberally
of such leaves as cabbage and other leafy vegetables,
the protein content of which in the fresh condition
does not as a rule exceed 2 per cent, the content of
other constituents of the diet in protein might not
be high enough to give the entire mixture consumed,
a protein content sufficiently high to promote growth
at the optimum rate.

McCollum and Davis, therefore, fed their rats a
diet which afforded them a choice among the follow-
ing list of foods: wheat, maize, rye and oat kernels,
cooked dry navy beans, peas, wheat germ, corn
gluten, wheat gluten, flax-seed oil meal, green clover,
green alfalfa leaves, onions and peanuts. It will be
observed that in this list there are several vegetable
foods having unusually high protein contents. Corn
gluten, which is a product of the corn starch manufac-
ture, contains about 25 per cent of protein; wheat
gluten, prepared by washing ground wheat free from
starph, contains about 86 per cent; flax-seed oil meal,


as much as 30 per cent, and wheat germ about 30 per
cent of protein. Since animals are known to grow
well on many diets containing 15 to 18 per cent
of protein, it seemed that with these things to
select from, one possible cause of failure in Slonaker's
experiments, viz., too low a protein intake, would be
avoided. McCollum and Davis had not at that time
discovered in the leaf the source of the dietary essen-
tial, fat-soluble A, although it is now known that the
leafy foods enable the herbivorous animal to thrive
on his diet derived entirely from plant tissues. It was
then assumed that when both the leaves and so
many different seeds as well as the germ was supplied
there could be little doubt that everything which a
herbivorous animal requires was present in the foods

The rats fed this wide variety of vegetable foods,
and with a most liberal supply of protein, duplicated
in all respects the results which Slonaker had de-
scribed. They grew at about half the normal rate
for the first few weeks, then became permanently
stunted, none ever reaching a size much greater than
half that of the average normal adult. The addition
of butter fat to the diet of some of these animals
failed to benefit them in any noticeable degree. The
answer to the question as to why rats do not thrive
on such strictly vegetarian food mixtures was not
secured from these experiments. It was, however,
soon after learned wherein lay the cause of failure of
animals so fed.


McCollum, Simmonds and Pitz, began in 1915 a
series of feeding experiments in which the diets of
rats were derived solely from a mixture of one seed
and one dry leaf. 2 In marked contrast to the failure
of animals to grow on any mixtures of seeds it was
found that in many cases a mixture of a seed with a
leaf formed a diet on which considerable growth
could be secured. Even polished rice, which as has
been already described, requires four types of
supplementing, viz, protein, mineral salts, fat-
soluble A and water-soluble B, before it becomes
dietetically complete, was found to induce fairly
good growth when fed with ground alfalfa leaves in
the proportion of 60 per cent of the former to 40 per
cent of the latter. On this simple monotonous mix-
ture, young rats grew from weaning time to 83 per
cent of the normal adult ?ze, and one female even
produced two litters of young, both of which were,
however, allowed to die within a few days. A mix-
ture of rolled oats, 60 per cent, and alfalfa leaves,
40 per cent, ground together makes a very much
better diet. On this simple mixture young rats have
been observed to grow to the normal adult size, and
to reproduce and rear young. One female reared
fourteen out of seventeen young born in three litters.
Maize and alfalfa leaf, wheat and alfalfa leaf, are
not so satisfactory for the production of growth as
is a mixture of rolled oats and alfalfa leaves. Mix-
tures of the latter leaf with legume seeds, peas and
beans, give still poorer results. (Chart 6.) These


results made it evident that there is nothing in
vegetarianism per se, which makes it* impossible to
nourish an omnivorous animal in a satisfactory
manner. It is only necessary to make a proper selec-
tion of food-stuffs, and to combine them in the right
proportions. In all the experiments described, in
which the diet was made up of so simple a mixture
as one leaf and one seed, they had not obtained
the optimum of growth, reproduction or rearing of

It seemed probable that the reason why they did
not more closely approximate the optimum in the
nutrition of animals restricted to a cereal grain and
a leaf, might he in too low a protein mixture, or a
protein mixture which was not of very high bio-
logical value. In 1915, McCollum, Simmonds and
Pitz 3 fed a group of young rats on a monotonous
mixture consisting of maize 50 per cent, alfalfa
leaf (dry) 30 per cent, and cooked (dried) peas, sub-
sequently dried, 20 per cent. The three ingredients
were ground together so finely that they could not
be picked out and eaten separately. This diet in-
duced growl h at approximately the normal rate and
the production and rearing of a considerable number
of young. The young grew up to the full adult size
and were successful in the rearing of their offspring.
Without ever tasting anything other than this mo-
notonous food mixture, as their sole source of nutri-
ment after the weaning period, this family of rats
remained nearly normal, and successfully weaned the


young of the fourth generation, with no apparent
diminution in Vitality. At this point the experiment
was discontinued.

The failure of Slonaker's rats to thrive on the
vegetarian diet is to be explained on the basis of
several faults. In the first place, the diet was of
such a nature that the animals could hardly do other-
wise than take a rather low protein intake. Sec-
ondly, the leaves, which formed the only constituents
of the food supply which contained enough mineral
elements to support growth, were fed in the fresh
condition. In this form the water content and bulk
is so great that it would be practically impossible
for an animal whose digestive apparatus is no more
capacious than that of an omnivora, to eat a sufficient
amount of leaf to correct the inorganic deficiencies
of the rest of the mixture, which consisted of grains,
seeds, tubers, and root foods. The same physical
limitations would likewise determine that the animals
would fail to secure enough of the fat^soluble A to
supplement the deficiency of all the ingredients of
their diet other than the leaves in respect to this
factor. This would not form so important a fault
as the inorganic deficiencies, but would be an im-
portant depressing factor. Thirdly, success or
failure would turn in great measure on the extent
to which the animals would be guided by instinct in
the selection of the proportions of the several types
of food-stuffs which was offered them. In the opin-
ion of the author the appetite is by no means so


safe a guide for the proper selection of foods as has
generally been supposed.

From the results of the experiments just de-
scribed it was necessary to conclude that the leaf
differs from the seed in that it contains in satis-
factory amounts the dietary factors which are found
in the seeds in too small amounts. These include the
three inorganic elements, calcium, sodium and chlo-
rine, the fat-soluble A and a protein supply which
supplements at least in some degree the proteins of
the seed. These, it will be remembered, are the
three and only purified food factors which need be
added to each of the seeds singly in order to make it
dietetically complete. It is therefore, possible to de-
vise a diet which is derived entirely from vegetable
materials which will produce normal growth and
the optimum physiological well-being.

At the Iowa Experiment Station, E ward 4 has con-
ducted extensive experiments of a character which
were intended to demonstrate that the appetite and
instincts of the hog serve to enable it to make such
an adjustment of the relative amounts of the several
food-stuffs offered it, as may induce better results
in the rate of growth than can be generally secured
when the adjustment is made by the feeder, and
the mixture of the ingredients of the ration are offered
in a form which admitted of no choice by the animal.
The data secured in many trials seem to show that
there is some basis for the belief that this element of
selection by the animal itself is worth taking ad-


vantage of. It should be mentioned that, as a rule,
in all these trials the animals were given a choice of
only three foods, one of these being a cereal grain,
another, a protein-rich food and a third a plant leaf.
In some experiments a salt mixture was made avail-
able. The reasons for the employment of the leaf
as a never failing constituent of the food supply of
the growing pig could not have been explained be-
fore the studies of McCollum and his co-workers,
with simplified diets and with diets restricted as to
source to a single food-stuff, and until the latter had
been fed with single and multiple food additions to
ascertain the exact nature of the dietary faults of
each. In connection with the types of diets em-
ployed by Eward it should be mentioned that in
case the animal ate fairly liberally of all the food-
stuffs offered him, a serious mistake would be
hardly made, since the proportions of the several con-
stituents eaten could be varied to a considerable de-
gree and growth still take place. In the case of the
mixture of maize 50 per cent, alfalfa leaves 30 and
peas 20, described above (Chart 7) it has been found
that for the rat these are the best proportions in
which these three ingredients can be mixed for the
promotion of growth and reproduction. It has been
further established that using these three food-stuffs,
a moderate amount of growth may be secured, but
few, if any, young will ever be produced if the mix-
ture fed contains more than 50 per cent or less than
20 per cent of alfalfa leaf. The importance of com-


bining the natural foods in the right proportions is
easily seen from these results. It is interesting to
note further, that shifting the proportions of maize,
peas and leaf in this mixture over a range of 20 per
cent does not materially change the protein content,
or indeed, the chemical composition of the food mix-
ture in any way, to a degree that could be expected to
make so great a difference in the state of nutrition
of the animals as is actually observed.

There are now available the results of a very ex-
tensive series of feeding trials in which the rations
were made up of one seed, one leaf and one legume
(pea, bean) in various proportions. These have
failed to reveal any mixture which is quite the equal
of the first ration of this type ever employed, viz.,
that composed of maize 50, alfalfa leaf 30 and peas 20
per cent. It is, of course, easily possible that better
mixtures of vegetable foods may be found by further
search, but these results show very definitely that
for the omnivorous type of animal, whose digestive
tract is so constituted that the consumption of large
volumes of leafy foods is not possible, it is by no
means a simple matter, if indeed possible, to derive
the diet entirely from the vegetable foods, and se-
cure the optimum of well-being. The data afforded
by the experiments described form a demonstration
of the fact that wide variety is of little value as a
safeguard to nutrition. Chemical analysis, no matter
how thorough, fails to throw much light upon the
dietary value of a food-stuff. The only way in which


the problems of nutrition can be solved is through
numerous properly planned feeding experiments,
but such studies were not possible before the solution
of the problem of successfully feeding mixtures of
purified food-stuffs. These studies led to the formula-
tion of an adequate working hypothesis repniing
what factors operate to make an adequate diet, and
made possible the interpretation of the cause of
success or of failure with diets of the complexity em-
ployed in daily life. It will be shown later that the
consumption of milk and its products forms the great-
est factor for the protection of mankind, in correcting
the faults in his otherwise vegetarian and meat diet.
The fact, that although the cereal grains each con-
tain every inorganic element which is contained in
an animal body, and every one which is a necessary
constituent of the diet, but in too small amounts
in the case of three of them, to enable the animals to
grow, revealed the mineral constituents of the diet
in a new and important light. The animal is sensi-
tive to either the actual amounts of certain of the
mineral elements in the food mixture, or to the re-
lationships among them. Sidney Ringer was led
in 1891 to his description of Ringer's solution, as the
result of the observations in physiology, that muscle
behaves more nearly normally in solutions con-
taining certain salts in definite proportions. Ringer's
solution contains, for each 100 molecules of sodium
chloride, two molecules of calcium chloride and two
to one molecules of potassium chloride, together with


a trace of a magnesium salt. Loeb, 5 Howell 6 and
others had described many experiments showing the
profound effects upon the subsequent development
of the eggs of varying in certain ways the composition
of the salt solutions in which unfertilized eggs of
certain marine animals were kept. In this way the
earliest stages of development which are ordinarily
observed only in the fertilized egg, could be caused
to take place in eggs into which no sperm had en-
tered. In the nutrition of the higher animals, it had
never been made clear how dependent the organism
is on the rate at which the blood stream receives
mineral nutrient. The fact that the cereal grains
are too low in three inorganic elements to admit of
growth, made it clear that food packages just as they
come from the hand of Nature, are not necessarily
so constituted as to promote health.

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