Chambers's Journal of Popular Literature, Science, and Art, Fifth Series, No. 15, Vol. I, April 12, 1884

by Various

We thus discover that, apart altogether from the every-day labour of life, in which brain and muscles engage, an immense amount of work is performed in the mere act of keeping ourselves alive. Nowhere in nature is work performed without proportionate waste, or wear and tear of the machine that works. This dictum holds quite as true of the human body as of the steam-engine. And as the engine or other machine requires to be supplied with the conditions necessary for the production of force, so the living body similarly demands a supply of material from which its energy (or the power of doing work) can be derived. As the engine obtains the necessary conditions from the fuel and water it consumes, so the living body derives its energy from the food upon which it subsists. Food in this light is therefore merely matter taken from the outside world, and from which our bodies derive the substances required for the repair of the waste which the continual work of life entails. In the young, food serves a double purpose—it supplies material for growth, and it also affords substance from which the supply of force is derived. In the adult, whilst no doubt, to a certain extent, the food supplies actual loss of substance, it is more especially devoted to the performance of work, and of maintaining that equilibrium or balance between work and repair, which, as we have seen, constitutes health.

Viewed in this light, the first important rule for food-taking is founded on the plain fact, that in the food we must find the substances necessary for the repair of our bodies, and for the production of the energy through which work is performed. Food-substances in this light fall into two well-marked classes—namely, into Nitrogenous and Non-nitrogenous substances. Another classification of foods divides them into organic and inorganic, the former being derived from animals and plants—that is, from living beings—while the latter are derived from the world of non-living matter. Thus, animal and plant substances represent organic foods; while water and minerals, both of which are absolutely essential for the support of the body, represent inorganic food materials. It would appear that from living matter alone, do we obtain the materials for generating force. The inorganic water and minerals, however, appear to be absolutely necessary for the chemical alterations and changes which are continually taking place within the body.

Adopting the classification of foods into the Nitrogenous and Non-nitrogenous groups, we discover examples of the first class in such substances as albumen, seen familiarly in white of egg and other substances; gluten, found in flour; gelatin, obtained from hoofs and horns; legumin, obtained from certain vegetables; casein, found in milk; and allied chemical substances. These substances possess a remarkable similarity or uniformity of composition. It would appear that in the process of digestion they are reduced to a nearly similar state, and on this account they can replace one another to a certain extent in the dietaries of mankind.

The nitrogenous foods have often been popularly termed ‘flesh-formers,’ and doubtless this name is well merited. For, as the result of experiment, it would seem that the chief duty performed by the nitrogenous parts of our food is that of building up and repairing the tissues of the body. They also produce heat, through being chemically changed in the blood, and thus aid in the production of force or energy. But it would also appear tolerably certain, that in a complex fashion the nitrogenous parts of our bodies assist or regulate in a very exact manner the oxidation or chemical combustion of the tissues.

It should be noted that nitrogenous foods are composed chemically of the four elements, carbon, hydrogen, oxygen, and nitrogen; the presence of the last element giving the characteristic name and chemical features to the group. Most of these foods in addition contain small proportions of sulphur and phosphorus.

An interesting advance in our knowledge of the part played by nitrogenous foods in the work of the body was made, when an idea of Liebig was overthrown by later experimentation. Liebig supposed that the nitrogenous foods required first to be actually converted into tissue—that is, into bodily substance—before their energy or work-producing power could be liberated. In this view, muscular force, through which we move, was believed to be dependent on the changes, destructive or otherwise, which take place in the muscles. The substance called urea, chiefly given off as a waste product by the kidneys and chemically representing nitrogenous waste, was in Liebig’s view regarded as representing the results of muscular force which had been exerted. But two scientists, Fick and Wislicenus of Zurich, proved, by a laborious series of personal experiments in mountain ascents, that a non-nitrogenous diet will maintain the body for a short time during the performance of severe work, no great increase in the amount of urea given off being noticed. The work in question was proved to have been performed on the carbon and hydrogen of the food consumed. These experiments have led to the now accepted view, that a muscle, instead of losing substance during work and thus wasting, in reality consumes nitrogen, and grows. The exhaustion of the muscle is dependent not so much on chemical waste, as on the accumulation within it of the waste products of other foods. The muscle, in other words, is merely the agent whereby so much energy, derived from the food, is converted into actual and applied force. Did muscle really waste, as Liebig supposed, the heart’s substance would be entirely consumed by its work of one week!

Such being the functions and nature of nitrogenous foods, we may now glance at the non-nitrogenous division. Four groups of foods are included in this latter class—namely (1) Starches and sugars, or ‘amyloids’ as they are often termed; (2) fats and oils; (3) minerals; (4) water. The starches and sugars include not merely starch and sugar, as ordinarily known, but various gums, and certain acids, such as lactic and acetic acids. Starch, as in bread, is a most important food. These foods appear to go directly to maintain animal heat, and to give energy, or the power of doing work, to the animal frame. The heat-producing powers of starches and sugars are certainly inferior to those of the fats and oils. But starches and sugars can be converted into fat within the system; and hence persons who suffer from a tendency to obesity are warned to exclude these foods from their dietaries. Starches and sugars likewise appear to assist in some measure the digestion of nitrogenous foods. That fats and oils are heat-producing foods is a fact taught us by the common experience of mankind that northern nations consume the greatest proportion of fat. The heat-producing powers of fat have been set down at two and a half times as great as those of starch and sugar; and there is no doubt that, in addition to assisting in the conversion of food into body substances, the fatty parts of our food also assist in the work of removing waste matters from the body. Fat, in addition, being chemically burned in the blood, gives rise to the force which we exert in ordinary muscular work.

The mineral parts of our food play an important part in the maintenance of the frame. We thus require iron for the blood, phosphorus for the brain and nerves, and lime for the bones; whilst a variety of other minerals is likewise found in the blood and other fluids of the frame. The uses of the mineral constituents of our body are still a matter of speculation. Small as may be the quantity of certain minerals required for the support of the body, serious health-derangement may result when we are deprived of these substances. Thus, scurvy appears to be a disease associated with the want of the mineral potash in the blood; and the cure of this disease is therefore accomplished when we supply to the blood those mineral elements which have previously been deficient. Common salt, or chloride of sodium, as it is chemically termed, although not entering into the composition of the body, appears to form an important part of all the secretions; and there can be little doubt that this mineral aids the formation and chemical integrity of the gastric juice of the stomach.

Water forms the last item in the list of non-nitrogenous foods. Of all foods, perhaps, water is the most important, seeing that it is a substance which, in the absence of all other nourishment, can sustain life for a period numbering many days. Thus, whilst a man dies in from six to seven days when deprived of solid food and water, life may be prolonged to as many as sixty days on water alone. The high importance of water as a food is abundantly proved, when we discover that it constitutes about two-thirds of the weight of the body; that it enters into the composition of the brain to the extent of eighty per cent.; that the blood consists of nearly eighty per cent. of water; and that even bone contains ten per cent. of this fluid. Entering thus into the composition of every fluid and tissue of the body, and being perpetually given off from lungs, skin, and kidneys in the ordinary work of life, there is little wonder that water assumes the first place amongst foods. Regarding the uses of water as a food, we see that it dissolves and conveys other foods throughout the system; that it assists in removing waste products; and that it also takes a share in regulating the temperature of the body through its evaporation on the skin.

Having thus considered the chemistry of foods, we may now pass to discuss the natural rules which science describes for the health-regulation of life in the matter of diet. A primary rule for food-taking is that which shows that, for the due support of the body, we require a combination of nitrogenous and non-nitrogenous foods. This fact is proved by the consideration that milk, ‘nature’s own food,’ on which the human being grows rapidly in early life, is a compound of both classes of foods. So also, in an egg, from which is formed an animal body, we find a combination of the two classes. Death results if we attempt to feed on either class alone; and as the body consists of both classes of substances, the justification for the combination of foods is complete. Man can obtain the required combination of nitrogenous and non-nitrogenous foods from animals alone, from vegetables alone, or from animals and vegetables combined. The water, of course, which is an absolutely essential feature of all dietaries, is regarded as an additional item. In regulating the dietary of mankind, it is found that the food of nations is determined largely, or completely, by their situation on the earth’s surface. Thus, the northern nations are largely animal feeders; whilst the southern peoples of the world are to a great extent vegetarians. Individual experience and taste produce amongst the units of a nation special proclivities in the way of diet. But we can readily see that mankind, with that elasticity of constitution and power to avail themselves of their surroundings, can adapt themselves to their environments, and become animal feeders, vegetable feeders, or subsist on a mixed dietary at will. This is the true solution of the vegetarian controversy. It is climate and race which determine the food of a nation. It is individual intelligence, liking, and constitution which determine variations and departures from the dietaries of the race.