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By food elements the reader is not to understand, chemical elements. The chemical elements--nitrogen, carbon, iron, calcium, etc.--in foods were named in the preceding chapter. By food elements is meant the various distinct compounds that exist in foods and that are useful, after digestion, as nourishment for the body. The chemical elements of the body do not exist in the body in their "free" (uncombined) or pure state. They are always present in various complex combinations, both in the human body and in the simplest forms of food-stuffs. The animal body does not make use of the "free" elements, with the exception of oxygen, but employs only certain acceptable compounds prepared by the synthetic processes of the plant. The plant is the ultimate source of all animal food.
Foods are materials which supply the "elements" necessary for promoting growth of the body and repairing its waste, yield energy for muscular work, yield heat, regulate the body processes, and make reproduction possible. According to their chemical composition, foods are classified as:
Carbohydrates (starches and sugars).
Hydrocarbons (fats and oils).
According to their functions, foods are divided into:
According to their sources, foods are classified as:
Food substances as they come from the plant and animal contain: (1) Nutritive matter; (2) Water; (3) Refuse--or waste. The different articles of food are placed into different classes according to the food elements that predominate. Thus, there are protein foods, carbohydrate foods, hydrocarbon foods and foods rich in organic salts, vitamins and water. Let us briefly discuss each of these classes of food substances and notice the chief sources of each.
These are rich in protein which contains nitrogen as a distinguishing element. Proteins also contain carbon, hydrogen and oxygen. Most proteins contain sulphur and some other elements. Chief among the protein foods are:
Nuts--all kinds except chestnuts, cocoanuts and acorns.
Legumes--beans, peas, lentils, peanuts.
Lean meats of all kinds--including fish, poultry, etc.
The plant and animal proteins most commonly met with in physiology are collectively designated "native proteins." This is a more or less arbitrary classification for which there seems to be little need. Formerly there existed considerable confusion in naming and classifying proteins and we still meet some differences of usage in the literature of the subject, but the tendency is more and more to follow the recommendations of the joint committee of the American Physiological Society and the American Society of Biological Chemists made in 1907. The following classification follows this recommendation in general:
1. Simple Proteins: These are defined as proteins that yield only amino acids or their derivatives on digestion or hydrolysis. This definition, however, is faulty as many of these proteins have been shown to have some carbohydrate material in their composition. Among these are:
A. Albumens: egg albumen, lactalbumen, serum albumen are of animal origin. Albumens of plant origin are legumelin of peas and leucosin of wheat.
B. Globulins: egg globulin, lactoglobulin, serum globulin, fibrinogen of the blood, myosin (muscle globulin) are of animal origin. Of plant origin are legumin of peas, tuberin of potatoes, edestin of wheat and seeds, and excelsin of the Brazil nut.
D. Albuminoids, or Scleroproteins: These are found in the connective tissues of the body. Among these are collagen which forms the ground substance of bone and cartilage and in the white fibrous or inelastic connective tissue (tendons, aponeuroses, ligaments, dura mater, pericardium, fascia); elastin found in the yellow (elastic) connective tissues in the walls of the blood vessels (especially arteries), and of the air tubes of the lungs; keratin, found in the outer layer of the skin and in nails, hair, feathers, hooves, etc.
E. Glutelins: Glutenin of wheat is an example of the glutelins.
F. Prolamines: Gliadin of wheat, zein of corn, and hordein of barley are examples.
2. Compound (complex or conjugated) Proteins: These are composed of a simple protein united with some other substance and are named according to the character of the other substance, as:
A. Chromoproteins: a simple protein united with a pigment--hemoglobin is an example.
B. Nucleoproteins: One or more simple proteins united with nucleic acid found chiefly in the nuclei of the cells, but also in the germ of wheat and in the thymus gland.
C. Phosphoproteins: Proteins containing phosphorus, as ovo-vitelin (vitelin of egg yolk), casein or caseinogen of milk.
D. Glycoproteins: A protein united with carbohydrate as mucin in saliva and mucus.
E. Lecithoproteins, or Lecithans: a protein united with lecithin, a compound of fat containing phosphorus and nitrogen and found in the brain, seminal fluid, and in many plants.
3. Derived Proteins: Proteins produced from the previously named proteins in various ways, but chiefly by means of digestion or hydrolysis, that is, by the action of digestive enzymes and by acids and alkalies. These are:
A. Coagulated protein, formed by heat.
B. Acid Metaproteins formed by the action of acids.
C. Alkali Metaproteins formed by the action of alkalis.
D. Casein, Fibrin.
E. Secondary Derivatives formed in the process of digestion--peptoses or albumoses, peptones and peptoids or peptids.
Every species of plant and animal has its own characteristic proteins. The proteins of closely related species are different. Indeed the proteins of different structures of the same organism are different. It has been estimated that there are 1600 different proteins in the human body. Similar complexity of protein constitution exists in the tissues of practically all animals. Each plant, also, possesses several different proteins in its makeup, each different tissue possessing its own characteristic protein. The proteins of the food supply are very different to those of the animal taking that food. These have to be broken down and reconverted into proteins peculiar to the eater.
When protein digestion is completed the protein has been broken down into simpler compounds known as amino acids. These are organic acids containing nitrogen. It does not seem necessary that I here enter into any detailed and technical discussion of the complexities of their chemical constitution. This can be of no value to my lay readers and my professional readers may consult their text books and reference books to refresh their memories upon this subject.
Amino acids, called also, the "building stones of the body," are much talked about today. Indeed, it begins to look as though they are now to go through the same over-emphasis, high pressure consideration and commercial exploitation that the vitamins are just now beginning to emerge from. Already synthetic amino acids and amino acids extracted from food sources are offered for sale to the food-conscious public. These offers are accompanied with the usual misleading and unfounded claims for their superior virtues.
The body cannot absorb any protein as such. If protein is absorbed directly into the blood stream, without first undergoing the processes of digestion, it is poisonous. Proteins must be broken down into simpler compounds known as amino acids before they can be absorbed and assimilated. Introduce the amino acids out of which proteins are made and all is well.
Proteins are colloids--amino acids are crystalloids. Plant and animal material should or must be in the colloidal state. Each plant and animal, however, must build its own colloids and in order that the animal body may utilize the substances in plant colloids in building its own colloids, it must first break them down into crystalloids.
While it is not entirely correct to speak of protein as containing such and such amino acids, for these are known to us only after the protein has been decomposed; still, for convenience we say proteins are made up of chemical units called amino acids, just as words are made up of letters. Just as the twenty-six letter of the alphabet are sufficient to form millions of words; so, the twenty-two or more amino acids are sufficient to form the many different proteins known and unknown. It is generally believed that there are amino acids that have not been isolated and identified.
Proteins are numerous, each one being different from every other. The protein molecule is exceedingly complex, containing from twelve to twenty different amino acids. Amino acids, themselves, are complex nitrogenous bodies, synthesized by plants in the process of growth. Animals are able only to analyze proteins in the process of digestion, and resynthesize the resulting amino acids into new and different proteins.
There exists a certain amount of confusion in naming and classifying the amino acids. Berg names the following twenty-one: glycocoll, alanin, serin, valin, leucin, isoleucin, asparaginic acid, asparagin, glutamin, arginin, ornithin, lysin, cystin, cystein, B-phenylalanin, tyrosin, trytophan, histidin, prolin, and oxyprolin.
Sherman lists the following twenty-two: glycine, alanine, valine, leucine, isoleucine, norleucine, phenylalanine, tyrosine, serine, theonine, cystine, methionine, aspartic acid, glutamic acid, hydroxyglutamic acid, argenine, lysine, histidine, proline, hydroxyproline, tryptophan and serine.
Amino acids serve the following five general functions in the animal body:
1. They serve as building stones out of which the proteins characteristic of the various cells of the body are synthesized. Thus, they serve as the materials of growth and repair.
2. The cells use them in manufacturing the many and various enzymes of the body, in producing the various hormones and in producing other nitrogenous products. They are supposed to be employed in the production of genes and antibodies; but as these two "substances" are merely hypothetical entities, who knows.
3. The blood proteins are made from the amino acids. These proteins, because of their colloidal osmotic pressure, are indispensable.
4. They are said to be used as a source of energy. In this the nitrogen of the amino acid is regarded as being of little value. But when the amine has been split off from the amino acid the remainder of the molecule, which constitutes the larger part of it, contains no nitrogen, but much carbon. Thus, if they are not immediately needed, certain of the amino acids, such as glycine, alanine, cystine and arginine are transformed into glucose and glycogen.
5. Some of the amino acids are supposed to serve certain specific functions. A deficiency of trytophan in young rats leads to cataract and blindness and to poor development of tooth enamel. In old as well as in young rats a lack of tryptophan causes blindness and impairs the generation of spermatozoa. Tryphtophan is essential to generation in rats. Tyrosine is thought to be essential to the production of the hormones adrenalin and thyroxin. A reduction of the number of spermatozoa is said to result from a deficiency of arganine.
The various amino acids are specific in their functions. They are not interchangeable. Of the twenty-two known amino acids only ten or twelve are regarded as essential or indispensable. Tryptophan, tyrosin, lysin, cystin, glutamic acid, histidin and ornathin are among the essential amino acids. If the diet supplies the essential amino acids in adequate quantities, growth, maintenance and reproduction are normal. If one or more of these is lacking or deficient this is not true. Examples: A deficiency of valine in the diet of young animals stunts growth and development to a remarkable degree. If lysin is lacking in the diet there is more or less maintenance but no growth. No matter how much protein and other elements supplied in the diet, if lysin and tryphtophan are lacking, life soon comes to an end.
It is held that the amino acids other than the ten or twelve indispensable ones can be made by the tissues from the essential amino acids, apparently by oxydizing them. Glycine apparently can be manufactured in the animal body from the other amino acids if it is lacking in the diet. Prolin, which may be readily produced in the body by oxidation of histidin is, therefore, not considered an essential amino acid. Its production from histidin depends, however, upon an over supply of this latter acid. Glycocoll is also of such constitution that it may be produced in the body by the oxidation of several different amino acids. Casein of milk is devoid of glycocoll, but rats fed upon casein thrive.
By an essential amino acid, then, is meant, one that the body cannot produce by oxidation (reduction) of another amino acid. The animal body cannot synthesize amino acids out of the elements of earth, air and water, but must receive these from the plant, which, alone, has the power to synthesize these substances. The animal body is capable only of producing some of the less complex amino acids out of the more complex ones by a reduction process.
Since the lower grade amino acids are formed within the body out of the higher compounds, they are regarded as of no vital importance. This, in my opinion, is a mistake. The body does seem to require them so that they are actually essential, even if it is not essential that they be taken in as such, but can be produced from other amino acids. On the other hand they can be produced from the higher amino acids only if these latter are present in excess of need. It may also be true that a saving of energy is secured if the lower grade amino acids are taken in with the food stuffs and the body is not compelled to reduce the higher compounds to lower grade. There is another theoretical possibility. The older theories of nutrition overlooked the universal validity of the Law of the Minimum to be explained in a later chapter. Investigators ignored the extent to which every tissue builder is dependent upon all the others. As Berg puts it: "They failed to realize that what is decisive for development, is not so much the absolute quantity of the various nutritive elements, as their relative proportions. They did not understand that the bodily need in respect of any one constituent of a diet can be determined only when we simultaneously take into account all the other factors of nutrition." There is the possibility that when one of the "non-essential" amino acids is lacking in the diet and the body is forced to make it from one of the essential amino acids, an actual reduction, below normal requirements, of the essential amino acid takes place with a corresponding lag in development.
Proteins are made up of amino acids. Some of these amino acids are indispensable, others may be made from the essential amino acids. No two proteins have the same amino acid content. Some of them are very deficient in one or more of the essential amino acids. Either the amino acid is entirely absent or it is present in such minute quantity that one would be forced to consume enormous quantities of the protein to secure an adequate supply of the deficient amino acid. Proteins lacking in an essential amino acid are inadequate proteins. According to their adequacy, individual proteins are grouped as:
1. Complete: Those maintaining life and providing for normal growth of the young and reproduction in the adult when fed as the sole protein food. Examples of complete proteins are excelsin of the Brazil nut, glycinin, of the soy-bean, casein and lactalbumen of milk, ovalbumen and ovovitallin of eggs, edestin, glutenin and maize glutellin of cereals. Rose showed that the proteins most suitable for maintaining growth in dogs are lactalbumen (milk), ovalbumen and ovavitellin (eggs); that next in order of suitableness are glutenin (wheat), casein (milk), glutelin (corn) and glycinin (soy bean). Gliadin (wheat and rye) and legumin (peas) are capable of maintaining nitrogen balance, but not growth. Zein and gelatin can do neither.
2. Partially Complete: Those maintaining life but not supporting normal growth. Examples of these are gliadin, of wheat, hordein of barley and prolamin of rye, legumin of peas, legumenin in the soy bean, conglutin, in blue and yellow lupin, phaseolin in the white kidney bean, legumin and vignin in vetch.
3. Incomplete: Those incapable either of maintaining life or of supporting growth. Gelatin from horn and other hard parts of the animal is the most conspicuous example of an incomplete protein, Zein of corn (maize) is another example of this class.
Let us take a look at an incomplete protein. With zein as the sole source of amino acids, growth is impossible. In fact, experimental animals fed zein as their sole protein, lose weight. If tryptophan is added to the zein, weight is maintained but growth does not occur. Only after both lysine and tryptophan are added can normal growth take place. Zein is deficient in tryptophan, glycine, lysine and glycocoll.
Gliadin, found abundantly in wheat and rye, lacks sufficient lusine to maintain growth. Gelatin lacks tyrosin and tryptophan. Unless these are supplied to the animal fed on gelatin as its sole source of protein, it soon dies.
Thus it may be seen that since the nutritive value of proteins is determined by the kinds and quantities of amino acids they contain, all proteins are not of equal value to the body and cannot be used interchangeably. The nutritive value of foods cannot be determined by reference to a table of food composition. This fallacy was exposed by Prof. Huxley many years ago. Sophie Leppel followed him in protesting against the belief that tables of food analysis give reliable indexes to food values. All the fuss made about the need for 118 grams of protein daily, without specifying the kinds of proteins, does not amount to much.
While I have emphasized the fact that the various proteins are not interchangeable, it is necessary to distinguish between the various isolated proteins and the common protein foods. All protein foods contain two or more proteins. The deficiencies of one protein of a food are often made up by the other protein of the same food. For example, tryptophan may be lacking in one protein and one of the other proteins in the same food may be rich in this amino acid. Returning to zein of corn, which, as we have seen, will not maintain life; it is supplemented by glutelin, of which the corn possesses almost an equal amount, and these two proteins are capable of supporting a normal rate of growth. Gliadin of wheat and rye lack sufficient lysine to maintain growth. But wheat contains other proteins which supply liberal portions of this amino acid.
We do not eat isolated individual proteins and do not depend upon but one such protein as our source of amino acids. On the contrary, we eat whole foods which contain two or several proteins. We also eat several foods, all of which contain proteins. Just as one protein in a food may supplement another protein in the same food, so the protein of one food may supplement the protein of another food. Two inadequate proteins may prove adequate when supplied to the same individual. This can be so, of course, only when they are not both inadequate in the same amino acids. If each is abundant in what is lacking in the other, the combined proteins will prove adequate. The sum total of the various proteins in the diet, if the diet is varied, will prove fully adequate.
It is customary to use young rats in testing the value of the various proteins. It is obvious to everyone that young rats never attempt to live on isolated and single proteins. They eat the whole food and eat different kinds of protein foods so that they receive all of the needed amino acids. Most of the experiments with the different vegetable and grain proteins have been made with denatured proteins and may not prove all that they are supposed to prove. They have been performed with isolated, individual proteins and Hindhede aptly says of these substances that, far from being remarkable that these isolated proteins have so little value, "it is remarkable that such substances, isolated by complicated chemical processes, have any value at all."
It may be ideal for experimental purposes, in testing the value of the different proteins, to use only single isolated proteins, but it is a far cry from this experimental condition to the eating practices of man and animals. It is not only true that the diets of both man and animals commonly contain more than one kind of protein food, but it is also true that all protein foods contain two or more proteins. If only a single protein food were consumed, the diet would contain more than one protein. Note the different proteins in corn, wheat, milk and eggs. It frequently happens that the protein in one food is abundant in the amino acids in which the protein in another food is deficient. Thus the two proteins supplement each other so that, together, they constitute a complete protein. Often the deficiency in a protein is so small that a very slight addition of the deficient amino acids from another source suffices to support normal growth and maintenance. All proteins are, therefore, capable of supplying the body with important nutritive substances. The mere fact that a protein is inadequate is not sufficient reason for rejecting it completely.
It is true that some mixtures of protein foods have been shown to be inferior, even, to certain single articles of protein. This is especially true of the grains as compared to milk. Some of the cereal proteins are adequate, but only so when fed in large amounts. Glutenin from wheat may be made to supply a sufficiency of amino acids in which it is deficient only by separating this protein from the wheat and feeding it in concentrated form and in amounts one could not secure by eating wheat. Edistin of hemp is another example of this kind. In small quantities it does not supply sufficient lusine. The same thing is true of the casein of milk. It is low in cystine, hence in small quantities, does not supply sufficient of this amino acid. Thus it becomes apparent that some complete proteins may prove to be partially incomplete when fed in reduced amounts.
A mixture of grains will not suffice to maintain growth and repair. Rye and barley are about the only grains that are adequate for the adult body. Even a mixture of as many as ten varieties of grains does not provide adequate protein for growth due to the fact that all of them are poor in lysin and cystin and most of them contain too little tryptophan.
In regular practice we do not consume casein as our sole source of protein, nor do we live upon an exclusive grain diet. We regularly consume many other protein-containing foods. Hygienists, on the other hand, have long contended that grains form no normal part of man's diet and have long considered them to be inferior foods. Dr. Densmore was the first to point out the inferiority of grains as an article of human consumption. We are not surprised that the experimenters have fully verified most of his contentions. More of this in a later chapter.
Animal experimenters are prone to overemphasize the importance of the food substances that they regularly use with which to supplement inadequate diets and to ignore, almost wholly, the natural order of feeding. For example, milk is a very handy item of food and is used very much as a dietary supplement in these experiments. It usually suffices to render adequate an otherwise inadequate experimental diet, hence the experimenters are prone to emphasize the "value" of milk and to completely ignore the obvious fact that in nature, animals secure an adequate diet without resort to milk after they are weaned. Their experimental diets are almost never the diets of the people; nor are they the diets of animals in nature. There is a tendency of this class of experiments to mislead both the experimenter and the people as a whole, inasmuch as they ignore the many other food supplements that are equally capable of supplementing the inadequacies of a monodiet or of a deficient but somewhat varied diet.
In experiments on dogs deficient diets were fed to a group of dogs. To this diet was added, for some of the dogs, a given quantity of milk. The dogs that got the milk grew and developed normally. The dogs not receiving the milk were stunted and poorly developed. It would be folly to reason from this that dogs require milk for normal development, for we know that dogs can and do develop normally without getting milk after they are weaned. All that such an experiment proves is that milk added to an otherwise deficient diet will render the diet adequate. But there are hundreds of other ways of rendering the diet adequate as all animals in the wild state are well aware. Indeed, it is probable that many of the other ways of rendering the diet adequate are superior to the milk. Milk after the normal suckling period has ended is far from being an unmixed blessing.
Experiments with the different proteins would easily lead the unwary to believe that the elephant, cow, horse, buffalo, deer, rabbit and other strictly vegetable eating animals cannot live and grow on their vegetable diets, but, actually, we know that they do very well on such diets. This is because they never eat but one kind of protein (never eat individual isolated proteins). Their diet is varied. One protein corrects the defects of another.
Another fact strikes the serious student of dietetics: namely, the experimenters never seem to consider nuts, which are certainly important constituents of man's normal diet, as worthy of their attention; yet most nuts contain complete and high grade proteins. Green vegetables also contain high grade proteins, although in very small amounts. But when these are added to the diet in large quantities, as in consuming large daily salads, they are capable of supplementing the deficiencies in an all-cereal diet and rendering this adequate. The experimenters are fond of comparing legumes and cereals with flesh foods, and neither of these classes of foods form parts' of man's normal diet.
The biological value of the different proteins is tested on animals, commonly on rats. These are rapidly growing animals. A protein may prove to be incomplete or partially complete when fed to animals of rapid growth and may prove to be complete when fed to animals of slow growth. No doubt, too, different species require the different amino acids in varying amounts, even for maintenance. We know that the protein in human milk is especially rich in tryptophan, more so than the protein of cow's milk, an amino acid vitally important in the growth of the infant and young child. No broad generalizations about the value of the different proteins are, therefore, possible. When a protein has been shown to be complete, partially complete or incomplete for a particular species it can be said to be so only for this species. It may prove to be otherwise when fed to another species with different requirements. The underworld notwithstanding, man is not yet a rat, and "rat-pen" results are not fully applicable to his nutrition. The final test must be upon man.
We are frequently told that meat protein is more easily assimilated than vegetable proteins. There is no evidence for this statement, but it may be argued on the other side that the frequency with which allergic manifestations follow the use of animal foods indicates that these are less easily assimilated than vegetable proteins. The assertion is based upon a failure to take into consideration, not the difficulties, but the differences (largely of timing) in the digestion of the various foods: not of various proteins, but of various foods.
Muscle meat, the kind most commonly consumed, is a very poor food. Its inadequacy is made manifest by the failure of captive lions to reproduce themselves on a diet preponderantly of this food. Berg says that the protein of potatoes is more efficiently utilized by the body than that of flesh. Hindhede has also shown the protein of potatoes to be adequate.
On the other hand, we are not concerned so much with the relative values of specific proteins, or even of the proteins of one protein-carrying food, but with the total value of all the proteins contained in our customary diet: and not with the proteins alone, but with the total diet. The whole question involved is best expressed thus: Is meat, as a whole, superior to vegetables as food? When we consume flesh or vegetables, we do not confine ourselves to their protein constituents, but eat the whole of them and they must be considered in their entirety.
There is nothing in the protein of the flesh that the animal did not derive from the plant. Not being able to synthesize amino acids, the animal merely appropriates these, ready-made, from the plant, in the form of plant proteins. Man can do this as efficiently and as easily as the lower animals. Plants yield up their amino acids to man as readily as to the cow.
Green vegetables contain proteins of a very high quality, though in small quantities. Nuts, on the other hand, rank with or even surpass, flesh foods in the quantity of their proteins, while their proteins are of equal rank with those of flesh. At the same time, nut proteins are "free from pathogenic bacterial or parasitical contamination," to use Clendening's words.
It is argued that plant proteins are "poor" because "they contain unnecessarily large amounts of some amino acids and little or none of others." It should not be overlooked, however, that we consume several vegetable protein foods and the deficiencies of one are made up by the richness of another. The excess of amino acids in vegetable proteins is never great.
That the individual proteins in grains and some other plant foods are physiologically inadequate is sufficiently demonstrated, but the sum-total of the various proteins in those foods, or shall we better say, in the diet as a whole, is usually fully adequate.
A protein is said to have higher physiologic or biologic value the smaller the amount of it required to supply the needs of the animal. Based upon this standard, the whole egg is ranked at 94; milk, 85; liver and kidney, 77; heart, 74; muscles meat, 69; whole wheat, 64; potato, 67; rolled oats, 65; whole corn, 60; white flour, 52; navy beans, 38. By this standard, vegetable proteins in general are said to be nearly always inferior to those of animal origin. The proteins of peanuts and soybeans are listed as exceptions, their proteins being complete. There is no appreciable difference between the muscle meat of cow, hog or sheep. These relative values were determined by tests made on rats, dogs, etc., and are not necessarily valid for human nutrition. It will be noted that nuts are again ignored in this classification of biologic values.
The fact that proteins are completely digested, that is broken up into their constituent amino acids before absorption proves, we believe, that highly complex proteins are not really wanted as foods. While it is true that it is part of the function of the digestive tract to extract impurities and non-congenial substances from the food and avoid these, it is not well to abuse the digestive system by foods that are too rich, that is, too complex. This will be made more clear in the chapter on food allergies.
The plant is the best and original source of building materials that our diet can supply. The really "vital and abiding union sought after in animal nutrition, is between the amino acids of the plant and the blood of the animal." In conformity with the principle of reciprocity and reciprocal differentiation operating in the organic world, we want in our diet proteins quite different from our own.
There is a tendency in many quarters to exalt meat proteins as superior to all other forms of protein. The adequacy of flesh proteins as growth factors is especially stressed. That flesh proteins contain all of the essential amino acids is frequently asserted. Meat (flesh) protein is the most valuable of all forms of protein, is a frequent assertion. Berg points out that "this cannot be accepted as a positive fact as regards the protein of individual muscles, only as regards the aggregate proteins of an animal body used as food." Abderhalden also points out this fact. This is especially true if the meat is not accompanied with a large supply of base-forming foods. Berg points out that carnivorous animals, living in a state of nature, "ensure a supply of bases by drinking the blood of their victims and devouring the bones and the cartilages as well as the flesh." It is also true that wild carnivores consume considerable quantities of fruits, berries and buds. Cats are often observed to eat vegetable foods. Wild carnivora especially eat such foods in the Autumn, although in the Spring they are likely to subsist exclusively upon the fruits of the kill.
It has long been known that if a dog is fed on flesh from which the juice has been extracted, he becomes emaciated after a time, toxic symptoms develop, and death rapidly follows. Skeletal changes characteristic of osteoporosis and oteomalacia are found upon postmortem examination. The extraction of the salts of the flesh causes death.
It is well to keep in mind that the different organs of the animal body differ in their amino acid content. As has been pointed out before, not merely every species of animal, but also, within each animal, every organ, has its own peculiar kind of protein. For this reason the different organs of the animal body are not equally complete or "valuable" as sources of amino acids. One advocate of flesh eating deplores the fact that "some patients are unfortunately averse to eating entrails. Entrails, like liver," he says, "kidneys, heart, spleen, etc., are extremely rich in certain vitamins and other valuable constituents and their regular use in this diet is to be greatly encouraged." To receive all the value of a flesh diet, it is necessary to eat the whole animal--not, however, as is the case in eating whole oysters, the feces, also.
We want, not merely amino acids, but amino acids in ideal combination with other indispensable substances--minerals, vitamins, carbohydrates--such as only plants can furnish. These other substances are essential to the full utilization of proteins. Meat protein, when deprived of its minerals, destroys life. Animal proteins are not ideally combined with these other substances. The most ideal substances for animal and human nutrition and the most ideal blends of these substances are to be found in the spare products of plants.
There is also a tendency of the experimenters to place too much importance on gains in weight. They find more rapid growth, or a greater gain in weight, or even greater ultimate growth, on some diets than on others. Too much reliance should not be placed in reported gains unless the kind of weight gained is specified. We are not interested in fattening beef cattle nor in mere bigness. Accelerated growth and precocious development are far from desirable accomplishments. Nor are results in one generation nor in a short time sufficient to establish the ultimate effects of a particular diet.
It is now asserted by all experimenters that the duration of the earlier dietetic experiments was usually too short. Berg says that his own first experiments lasted for a week. Later he extended them to two weeks, then to several months. It is now known that an experiment must often run through several generations to yield dependable results. Unfortunately the importance of the time factor is not yet fully appreciated. Nature has carried on countless dietetic experiments, lasting not just a few weeks, or a few generations, but for ages. Our experimenters have failed to notice the results of long-time experiments of this nature. Their belief in "struggle" and "survival" has prevented them from recognizing the role of nutrition in integration, disintegration and re-integration--in two words, evolution and degeneration.
The advocates of flesh eating are particularly prone to close their eyes to the results of ages of flesh eating. With no valid standard of normal growth, they fix their attention upon the growth promoting effects of flesh. They ignore the evils of precocious development and an accelerated growth. Their standard of mere bigness is the same as that of the stock raisers. One could easily think that they are growing children for the market; that the children, after they reach the "fryer" or "broiler" stages are to be sold by the pound. The larger they grow, the more money they will bring. Accelerated growth tends to be unbalanced growth. There is likely to be overgrowths and undergrowths that render the finished organism inferior. But, I must again emphasize, one generation or even three generations of such feeding is not sufficient to unfold its ultimate results.
This is the name given to certain organic compounds of carbon that are produced by plants in the process of growth from carbon, hydrogen and oxygen, with the oxygen and hydrogen in proportions to form water. In everyday language we know the most important of these carbohydrates as starches and sugars. As will be seen later, carbohydrates are complex substances composed, in most instances, of simpler substances, or building blocks, called sugars. Chief among the carbohydrates are:
Fruits--Bananas, all sweet fruits, hubbard squash, etc.
Nuts--A few varieties--acorns, chestnuts and cocoanuts.
Tubers--potatoes, sweet potatoes, carrots, artichokes, parsnips, etc.
Legumes--Most beans, except some varieties of soybeans, all peas, peanuts.
Cereals--All grains and practically all cereal products. (Gluten bread is not a carbohydrate.)
The reader will notice that grains and legumes are classed both as proteins and carbohydrates. This is due to the fact that they contain enough of each of these food elements to be placed in both classes. Nuts, for the same reason, are classed both as proteins and as fats. Milk, commonly classed as a protein is really low in protein. It may with equal justification be classed as a sugar or carbohydrate. All foods contain more or less carbohydrates, as they all contain more or less protein. Most foods contain some fats, but there is none in most fruits nor in the green leaves of vegetables.
Carbohydrates, like proteins, are composed of simpler compounds known as simple sugars or monosaccharides. According to their composition, these are classed as follows:
1. Monosaccharides: Sugars containing only one sugar group or radical. Among the monosaccharides are grape sugar (glucose or dextrose), fruit sugar (fructose or levulose), and galactose of honey. These are the assimilable forms of carbohydrate. Dextrose is the principle member of the glucose group and much less sweet than cane sugar. It is known as grape sugar and is found in fruits, some vegetables and honey. Glucose occurs in both plants and animals and is formed by the action of heat and the ultraviolet rays upon starch in the presence of an acid. Corn syrup is commercially known as glucose. Glucose may also be made by treating starch with sulphuric acid in the presence of heat. Fructose and levulose are derived from fruits and honey. Galactose is a crystaline glucose obtained by treating milk sugar with dilute acids.
2. Disaccharides: Sugars containing two simple sugars, or that can be broken into two monosaccharides. The ordinary cane sugar or sucrose of commerce is a disaccharide composed of glucose and galactose. Invert sugar found in honey is a mixture of glucose and fructose. Maltose or malt sugar is composed of galactose and glucose. Maple sugar (sucrose) and milk sugar (lactose) are also disaccharides.
3. Trisaccharides: Sugars containing three sugar groups or radicals. Beet sugar is the best known example of this sugar.
4. Polysaccharides: Colloids or non-crystalizable organic substances known as starches. There are three main groups of polysaccharides: 1. Starches; 2. glycogen (animal starch), and 3. pentosans. Pentosans are numerous and include the cellulose or woody fibre of cotton, linen, walls of plant cells, etc. They are usually indigestible, although, in tender cabbage and other very tender vegetables, they are digestible. Galactose found in sugar, seeds, and algae; pectans found in unripe fruit and the gummy exudate on trees and plants are also pentosans.
Starches and sugars are well known to everyone as they are found in all fruits and vegetables. Sugars are soluble carbohydrates with a more or less sweet taste. When heated to a high temperature they form caramel. Sugars are crystalloids, starches are insoluble and are colloids. Glycogen and milk sugar are the only carbohydrates of animal origin and even these are derived originally from the plant. Animals are incapable of extracting carbon from the air and synthesizing carbohydrates.
While the sugars are all soluble, raw starch is insoluble. Boiling will render part of it soluble. This, however, as will be shown in a later chapter, hinders its digestion. Starch is converted into a disaccharide in the mouth and this is, then, converted into a monosaccharide in the intestine.
The body cannot use starch. It must first be converted into sugar before it can be utilized by the cells. This is done in the process of digestion and begins in the mouth. Disaccharides and polysaccharides are converted into monosaccharides in the process of digestion, as carbohydrates can be absorbed and assimilated only as monosaccharides. Starch must first be converted into sugar and the complex sugars must be converted into simple sugars before they are absorbed. The body's need for sugar may easily be supplied without eating commercial sugars and syrups, or any form of denatured carbohydrate. Child and adult, alike, should eat only natural sweets and starches.
Sugar is the most important building material in the plant world. A characteristic difference between plants and animals is that, whereas, the animal is built up largely out of proteins, the plant is built up largely out of carbohydrates. Plants may be truly said to be made of sugar. They contain various minerals and some nitrogen, but practically the whole fabric of the plant or tree is composed of sugar in some form. Sugars are essential constituents of all plants without which they cannot exist. Indeed, sugars are the most important and most abundant building materials in plants. Out of the immature or sap sugars plants build their roots, stems, flowers, fruits and seeds. The finished plant is almost literally made of sugar.
Nature produces sugars out of three gases--carbon, oxygen and hydrogen. Oxygen and hydrogen in proportions to form water are taken from the water in the soil. Carbon is taken from the carbon dioxide of the air. Out of these gases, or out of this fluid and gas, the plant synthesizes sugar, a thing the animal cannot do. The green coloring of plants is due to the presence of a pigment known as chlorophyll. This pigment takes part in a chemical process known as photosynthesis, by which, carbon-dioxide (or, at least the carbon in the carbon-dioxide), with the aid of sunlight, is united with water to form sugar. Recent experiments have shown that enzymes contained in the leaves of the plants are the chief agents in the production of this sugar. Some plants can produce sugar in the absence of light.
Not only the starches of plants, but also the pentosans, the woody fibers, cellulose and gums are made of sugar and may be reconverted into sugar. When carbohydrates are stored for long periods they are stored as starches. When they are used, they are reconverted into sugars. Corn, peas, etc., are sweet (full of sugar) before they mature. The sap of the corn is also sweet. The sap of the cane plant is very sweet. In the matured state, corn, cane seed and peas are hard starch grains. In the germinating process the starch is reconverted into sugar. As starches, these seeds will keep for long periods of time; as sugars they would not keep until the following spring. It will be noticed that the enzymes in seed do not require ultra violet rays and acid to bring about this reconversion, any more than do the enzymes in digestive juices.
Fruits are ready for immediate use and if not used soon after ripening, tend to decompose rapidly. Grains are intended for storage. It is significant that fruits are composed of insoluble starches and are usually rich in acids before they ripen. In this state they are usually avoided by animals. The starch is reconverted into sugar in the ripening process. This arrangement protects the seed of the fruit until it is matured and ready for dispersal. Then the fruit is ripened and made ready for food.
The animal, like the plant, builds its carbohydrates out of sugar. All starch foods must be converted into sugar (in the process of digestion) before they can be taken into the body and used. Animal starch (glycogen) is made from sugar. It, like the starch of grains, is a storage product. Like the starch of grains, it must be reconverted into sugar before using. The sugar in milk may be made from starches.
The matured or fruit sugars of plants, especially those of fruits, are particularly appropriate for food. They are never concentrated and are always well balanced with other ingredients. They are built up out of the immature sugar and impart to both fresh and dried fruits their delicious flavors. Matured sugars in flowers are collected by bees and made into honey. Fruit sugars are, in truth, export products produced by plants.
All the sugar the body requires may be obtained from fresh ripe fruits. This is especially so during the summer months. During the winter months when fresh fruits are not so abundant, dried (but unsulphured) fruits are excellent sources of sugar. These should not be cooked. Owing to the absence of water, dried fruits are more concentrated foods then fresh fruits and should not be eaten in the same bulk.
Just as fruits are savoured with their matured sugars, so vegetable foods are savoured with the immature juices (saps) of the plants. In the plants, as in the fruits, the sugars are combined with vitamins, mineral salts, fibre and other elements of foods.
It is essential to emphasize that sugars constitute but one of the ingredients of plant life and are never put up in their pure state. In fruits and plants they are always combined with and balanced by other ingredients, particularly with salts, vitamins and water. Man, not nature, produces concentrated sugars. Man, not nature, separates the minerals from sugar. Sugars should be eaten as nature provides them.
Commercial syrups and molasses are concentrated saps. Besides being concentrated, usually by the use of heat in evaporating the water, they are commonly deprived of their minerals and vitamins, often have preservatives, artificial colors and flavors added and are often bleached with sulphur dioxide, with which they become saturated. Commercial sugars--maple, cane, beet, milk--are crystallized saps. They too, are unbalanced, commonly bleached, and thoroughly unfitted for use. So concentrated are these syrups and sugars, so denatured and so prone to speedy fermentation in the digestive tract, that it is best not to employ them at all. If they are used they should be used very sparingly. The same rule should apply to honey. This food of the bee contains all the other nutritive elements in very minute quantities, being largely water and sugar with flavors from the flowers. If it is eaten, it should be taken sparingly.
What a difference between eating sugar cane and eating the extracted, concentrated and refined sugar of the cane! It is said that it takes a West Indian native an hour to chew eighteen inches of cane from which he derives the equivalent of one large lump of sugar--less than the average coffee-drinker puts into a single cup of his favorite poison. (The boys and girls of Texas and Louisiana can chew sugar cane faster than the West Indian native, it seems.) In thus securing his sugar, the cane-eater secures the minerals and vitamins that are normally associated with sugars--he does not eat a "purified" product.
Sugar is regarded as an energy food, but it is a remarkable fact that the heavy sugar-eater prefers to watch athletic games to taking part in them. We, of course, have reference to the heavy-eater of commercial sugars. They seem to stimulate and then depress the muscular powers.
It has long been the Hygienic theory that the catarrhal diseases are based on carbohydrate excess--sugar excess, as all starches are converted into sugar in digestion. It is interesting to note, in this connection, that the British Medical Journal for June 1933 carried an article discussing "the relation of excessive carbohydrate ingestion to catarrh and other diseases," in which it was pointed out that during World War I, the incidence of catarrhal illnesses was reduced seemingly corresponding with the great reduction of sugar consumption. The writer of the article concludes that "restriction in the use of sugar would result in improvement in the national health as regards catarrhal illness, as well as in other directions."
Hydrocarbon foods are those rich in hydrocarbon--fats and oils. Hydrocarbons are composed of carbon, hydrogen and oxygen. In the animal body, fats may be manufactured out of sugars and proteins. Fats are produced in the plant out of sugar. Chief among the hydrocarbon foods are:
Nuts--almost all varieties.
Legumes--peanuts, soy beans.
Dairy products--cream, butter and some cheese.
Flesh of dead animals, especially pork and mutton and beef that has been fattened. Fat fish--herring, shad, salmon, trout.
There are many kinds of fats--solid and liquid. Fats and oils are formed in plants, and fruits when ripening. A decrease in sugars accompanies the increase in fats. It is but another evidence of the importance of sugar in the life of the plant and, thereafter, in the life of the animal. While the animal is capable of synthesizing fats out of starches and sugars, it is not capable of taking hydrogen, oxygen and carbon and synthesizing fats out of these.
The fat of the animal differs from the oil of the plant, just as do the proteins of the animal differ from those of its food supply. Each animal builds its own characteristic fats out of its foods. Fats and oils are complex substances that are made up of simpler substances which we may call the "building stones" of fat. True fats are composed of fatty acids and glycerol--or glycerides. Fats differ according to the fatty acids and glycerides which they contain.
Stearic, palmitic butyric and oleac acids are the most common glycerides found in edible fats. The stearates are combinaitons of stearic acid with glycerol--stearin. Several fatty acids are present in all fats. In butter there are palmitic, oleic, myristic and butyric acids. Stearic acid is present in suet (hog fat), palmitic acid is abundant in vegetable and animal fats. Oleic acid is found in most fats and oils. Such vegetable oils as olive, cottonseed, peanut, almond and cocoanut oils contain large amounts of olein.
Fats are split up during the process of digestion into fatty acids and glycerol. Fats and oils, like proteins and carbohydrates, are not usable as such, but must be broken down into their constituent "building stones" and these "building stones"--fatty acids and glycerol--are used with which to build human fats.
Mendel asks "are there essential fatty acids that must be supplied in the diet because they cannot be produced de novo by the animal organism?" Although both he and Hindhede have shown that green stuff can take the place of fat in the diet, there are facts that lead us to believe that it is, at least, a great saving to the body if some fat is supplied.
Although the body can synthesize fats out of carbohydrates and proteins, there are certain fatty acids that it is incapable of synthesizing and these are essential to animal life. Three unsaturated fatty acids--linoleic, linolenic and arachaidonic--cannot be synthesized by the animal organism. Only one of these is considered essential, for, as in the case of certain amino acids, they can replace one another in animal nutrition. Rats fed on diets lacking in the essential fatty acids cease to grow, develop scaliness of the skin, caudal necrosis, emaciation, kidney lesions and early death. Certain blood deficiencies are also seen when these fatty acids are lacking in the diet of animals.
Besides the fatty acids supplied by the fats in our diet, fats also contain fat soluble vitamins and minerals. Large quantities of fat are not required, but a small quantity daily is essential to normal development and maintenance and to good health.
Fat serves as a protection and as a packing and support for organs, forms emulsions and lubricants, serves as storage for reserve "fuel," enters into the constituents of the walls of the body's cells, and is an essential element of the nervous system. Lecithin, a widely distributed fat is very important in human nutrition, being an essential ingredient of the brain and nerves and also of the semen. Lecithin contains, besides the fatty acids, phosphorus. Insufficient fat tends to lessen nervous efficiency.
On the whole, vegetable oils are superior to animal fats as human foods. Cream and butter (unpasteurized) are the best of the animal fats employed as foods. Fats, like sugars, are best taken as nature prepares them; that is in the foods in which they exist. Most nuts are rich in oil and form the best sources of fat for human consumption. Fats, when extracted from their sources, concentrated, purified, and preserved, form poor foods. Many of them have all their vitamins destroyed and are devoid of all minerals. For example, in the process of rendering hog fat into lard, the fat is boiled for a long period and everything skimmed from the top until nothing remains but "pure" fat. All the minerals and vitamins are destroyed and removed. Long cooked in this way, the lard is practically indigestible. Olive oil, peanut oil, soybean oil and other vegetable oils are best eaten in the fruits, legumes and other plant substances in which nature prepares them.
Fats must be digested before they can be used. The cells of the body cannot use complex fats. The fats must first be reduced to a few simple acceptable substances in the process of digestion. The skin is not a digestive organ. It is not able to take complex fats and break them down into their simpler constituents and then make use of the fatty acids and glycerol thus formed. For these reasons "skin foods," composed of some cream or oil, to be rubbed on or into the skin, cannot nourish the skin. They only grease it--that is, make it dirty. The skin must be fed from within. It contains very little fat and this must come from the blood. Blood is the only food of the tissues of the body. It is folly to try to feed our tissues with any other substances.
As separate chapters will be devoted to these two classes of substances, little more will be done here than to classify the chief sources of them. The mineral salts enter into the composition of every fluid and structure of the body. Inorganic salts cannot be substituted for them as will be shown in a subsequent chapter. The animal lacks the ability to take the crude elements of the earth and synthesize these into acceptable organic compounds.
Vitamins, of which there are a number, are also produced only by the plant. The animal body is capable of taking certain provitamins and completing their synthesis. But it is not capable of producing vitamins de novo. They serve as enzymes.
Vitamins and organic salts are distributed throughout nature and are present in varying quantities in all food substances. Fruits and fresh vegetables are especially high in them. Fruits and vegetables will be treated in separate chapters. Here we are interested in them, largely as sources of these food substances. Chief among these rich sources of vitamins and salts are:
(1) Succulent (watery, juicy) Vegetables:
Leafy Vegetables--celery, lettuce, kohlrabi, cabbage, spinach, dandelion, endive, turnip tops, mustard, parsley, cauliflower, Brussels sprouts, kale, chard, lotus, cress, field lettuce, romaine, chicory, rhubarb, beet tops, radish tops, etc.
Fruiting Plants--okra (gumbo), cucumbers, squash summer squash, pumpkin, string beans, green peas, corn "in milk" (fresh), etc.
Tubers--Asparagus, beet, carrot, turnip, radish, onion, cone artichoke, rutabaga, garlic, oyster plant (salsify).
(2) Juicy Fruits:
Acid: Orange (sour), lemon, lime, sour apple, grapefruit, pineapple, peach, sour plum, apricot, cranberry, loganberry, pomegranate, strawberry, tomato.
Sub-Acid: Melons--watermelons, musk-melon, cantaloupe, casaba, honey dew, etc.,--sweet grapes, huckleberry, fresh figs, pears, etc.
Many other foods are used, both in America and other parts of the world, but all may be placed in some one or the other of the above classes. Some foods such as nuts, grains and legumes, may be placed in two classes.
The bountiful hand of mother nature has supplied us with an abundant and pleasing variety of foods. This wonderful variety of foods which are designed to please the senses of sight, taste and smell, as well as supply the needs of the body, are all made of but a few simple elements of the soil--"the dust of the earth."
Together with water, oxygen and vitamins, proteins, carbohydrates, fats and minerals form the constituents of the body. These must be taken into the digestive tract and there prepared for the use of the body, before they are allowed to enter the body and before they become part of the body.
The material composing a leaf of lettuce cannot be anything but a leaf of lettuce, until it has died from that state and then, after it has been disintegrated, its elements may be built up into the tissues of man. Digestion is the disintegrating process.
Our present knowledge of the role of digestion in nutrition shows positively that the parental administration of food is without value. The process of digestion disintegrates food into fragments which represent the true nutrients--proteins are reduced to amino acids, carbohydrates to simple sugars, fats to fatty acids and glycerol and it is claimed that ions may be liberated from the organic salts during the process of digestion. These things serve as the structural or metabolic units and nothing else will or can.