THE SCIENCE OF NUTRITION

The importance of some general knowledge of the principles of nutrition and the nutritive values of foods is not generally realised. Ignorance on such a matter is not usually looked upon as a disgrace, but, on the contrary, it would be commonly thought far more reprehensible to lack the ability to conjugate the verb ‘to be’ than to lack a knowledge of the chemical properties of the food we eat, and the suitability of it to our organism. Yet the latter bears direct and intimate relation to man’s physical, mental, and moral well-being, while the former is but a ‘sapless, heartless thistle for pedantic chaffinches,’ as Jean Paul would say.

The human body is the most complicated machine conceivable, and as it is absurd to suppose that any tyro can take charge of so comparatively simple a piece of mechanism as a locomotive, how much more absurd is it to suppose the human body can be kept in fit condition, and worked satisfactorily, without at least some, if only slight, knowledge of the nature of its constitution, and an understanding of the means to satisfy its requirements? Only by study and observation comes the knowledge of how best to supply the required material which, by its oxidation in the body, repairs waste, gives warmth and produces energy.

Considering, then, that the majority of people are entirely ignorant both of the chemical constitution of the body, and the physiological relationship between the body and food, it is not surprising to observe that in respect to this question of caring for the body, making it grow and work and think, many come to grief, having breakdowns which are called by various big-sounding names. Indeed, to the student of dietetics, the surprise is that the body is so well able to withstand the abuse it receives.

It has already been explained in the previous essay how essential it is if we live in an artificial environment and depart from primitive habits, thereby losing natural instincts such as guide the wild animals, that we should study diet. No more need be said on this point. It may not be necessary that we should have some general knowledge of fundamental principles, and learn how to apply them with reasonable precision.

The chemical constitution of the human body is made up of a large variety of elements and compounds. From fifteen to twenty elements are found in it, chief among which are oxygen, hydrogen, carbon, nitrogen, calcium, phosphorus, sodium, and sulphur. The most important compounds are protein, hydrocarbons, carbohydrates, organic mineral matter, and water. The food which nourishes the body is composed of the same elements and compounds.

Food serves two purposes, it builds and repairs the body tissues, and it generates vital heat and energy, burning food as fuel. Protein and mineral matter serve the first purpose, and hydrocarbons (fats) and carbohydrates (sugars and starches) the second, although, if too much protein be assimilated it will be burnt as fuel, (but it is bad fuel as will be mentioned later), and if too much fat is consumed it will be stored away in the body as reserve supply. Most food contains some protein, fat, carbohydrates, mineral matter, and water, but the proportion varies very considerably in different foods.

Water is the most abundant compound in the body, forming on an average, over sixty per cent. of the body by weight. It cannot be burnt, but is a component part of all the tissues and is therefore an exceedingly, important food. Mineral matter forms approximately five or six per cent. of the body by weight. Phosphate of lime (calcium phosphate), builds bone; and many compounds of potassium, sodium, magnesium and iron are present in the body and are necessary nutrients. Under the term protein are included the principal nitrogenous compounds which make bone, muscle and other material. It forms about 15 per cent. of the body by weight, and, as mentioned above, is burnt as fuel for generating heat and energy. Carbohydrates form but a small proportion of the body-tissue, less than one per cent. Starches, sugars, and the fibre of plants, or cellulose, are included under this term. They serve the same purpose as fat.

All dietitians are agreed that protein is the essential combined in food. Deprivation of it quickly produces a starved physical condition. The actual quantity required cannot be determined with perfect accuracy, although estimates can be made approximately correct. The importance of the other nutrient compounds is but secondary. But the system must have all the nutrient compounds in correct proportions if it is to be maintained in perfect health. These proportions differ slightly according to the individual’s physical constitution, temperament and occupation.

Food replenishes waste caused by the continual wear and tear incidental to daily life: the wear and tear of the muscles in all physical exertion, of the brain in thinking, of the internal organs in the digestion of food, in all the intricate processes of metabolism, in the excretion of waste matter, and the secretion of vital fluids, etc. The ideal diet is one which replenishes waste with the smallest amount of suitable material, so that the system is kept in its normal condition of health at a minimum of expense of energy. The value, therefore, of some general knowledge of the chemical constituents of food is obvious. The diet must be properly balanced, that is, the food eaten must provide the nutrients the body requires, and not contain an excess of one element or a deficiency of another. It is impossible to substitute protein for fat, or vice versa, and get the same physiological result, although the human organism is wonderfully tolerant of abuse, and remarkably ingenious in its ability to adapt itself to abnormal conditions.

It has been argued that it is essentially necessary for a well-balanced dietary that the variety of food be large, or if the variety is to be for any reason restricted, it must be chosen with great discretion. Dietetic authorities are not agreed as to whether the variety should be large or small, but there is a concensus of opinion that, be it large or small, it should be selected with a view to supplying the proper nutrients in proper proportions. The arguments, so far as the writer understands them, for and against a large variety of foods, are as follows:

If the variety be large there is a temptation to over-feed. Appetite does not need to be goaded by tasty dishes; it does not need to be goaded at all. We should eat when hungry and until replenished; but to eat when not hungry in order to gratify a merely sensual appetite, to have dishes so spiced and concocted as to stimulate a jaded appetite by novelty of taste, is harmful to an extent but seldom realised. Hence the advisability, at least in the case of persons who have not attained self-mastery over sensual desire, of having little variety, for then, when the system is replenished, over-feeding is less likely to occur.

In this connection it should be remembered that in some parts of the world the poor, although possessing great strength and excellent health, live upon, and apparently relish, a dietary limited mostly to black bread and garlics, while among ourselves an ordinary person eats as many as fifty different foods in one day.

On the other hand, a too monotonous dietary, especially where people are accustomed to a large variety of mixed foods, fails to give the gustatory pleasure necessary for a healthy secretion of the digestive juices, and so may quite possibly result in indigestion. It is a matter of common observation that we are better able to digest food which we enjoy than that which we dislike, and as we live not upon what we eat, but upon what we digest, the importance of enjoying the food eaten is obvious.

Also as few people know anything about the nutritive value of foods, they stand a better chance, if they eat a large variety, of procuring the required quantity of different nutrients than when restricted to a very limited dietary, because, if the dietary be very limited they might by accident choose as their mainstay some food that was badly balanced in the different nutrients, perhaps wholly lacking in protein. It is lamentable that there is such ignorance on such an all-important subject. However, we have to consider things as they are and not as they ought to be.

Perhaps the best way is to have different food at different meals, without indulging in many varieties at one meal. Thus taste can be satisfied, while the temptation to eat merely for the sake of eating is less likely to arise.

It might be mentioned, in passing, that in the opinion of the best modern authorities the average person eats far more than he needs, and that this excess inevitably results in pathological conditions. Voit’s estimate of what food the average person requires daily was based upon observation of what people do eat, not upon what they should eat. Obviously such an estimate is valueless. As well argue that an ounce of tobacco daily is what an ordinary person should smoke because it is the amount which the average smoker consumes.

A vegetarian needs only to consider the amount of protein necessary, and obtained from the food eaten. The other nutrients will be supplied in proportions correct enough to satisfy the body requirements under normal conditions of health. The only thing to take note of is that more fat and carbohydrates are needed in cold weather than hot, the body requiring more fuel for warmth. But even this is not essential: the essential thing is to have the required amount of protein. In passing, it is interesting to observe the following: the fact that in a mixed fruitarian diet the proportion of the nutrient compounds is such as to satisfy natural requirements is another proof of the suitability of the vegetable regimen to the human organism. It is a provision of Nature that those foods man’s digestive organs are constructed to assimilate with facility, and man’s organs of taste, smell, and perception best prefer, are those foods containing chemical compounds in proportions best suited to nourish his body.

One of the many reasons why flesh-eating is deleterious is that flesh is an ill-balanced food, containing, as it does, considerable protein and fat, but no carbohydrates or neutralising salts whatever. As the body requires three to four times more carbohydrates than protein, and protein cannot be properly assimilated without organic minerals, it is seen that with the customary ‘bread, meat and boiled potatoes’ diet, this proportion is not obtained. Prof. Chittenden holds the opinion that the majority of people partake greatly in excess of food rich in protein.

No hard and fast rule can be laid down to different persons require different foods and foods and amounts at different times under different regulate the amount, or proper proportions, of food material for a well-balanced dietary, as amounts, and the same person requires different ferent conditions. Professor W. O. Atwater, an American, makes the following statement: ’As the habits and conditions of individuals differ, so, too, their needs for nourishment differ, and their food should be adapted to their particular requirements. It has been estimated that an average man at moderately active labor, like a carpenter, or mason, should have (daily) about 115 grams (1750 grains) or 0.25 pound of available protein, and sufficient fuel ingredients in addition to make the fuel value of the whole diet 3,400 calories; while a man at sedentary employment would be well nourished with 92 grams (1400 grains) or 0.20 pound of available protein, and enough fat and carbohydrates in addition to yield 2,700 calories of energy. The demands are, however, variable, increasing and decreasing with increase and decrease of muscular work, or as other needs of the person change. Each person, too, should learn by experience what kinds of food yield him nourishment with the least discomfort, and should avoid those which do not “agree” with him.’

It has been stated that unless the body is supplied with protein, hunger will be felt, no matter if the stomach be over-loaded with non-nitrogenous food. If a hungry man ate heartily of only such foods as fresh fruit and green vegetables he might soon experience a feeling of fulness, but his hunger would not be appeased. Nature asks for protein, and hunger will continue so long as this want remains unsatisfied. Similarly as food is the first necessity of life, so is protein the first necessity in food. If a person were deprived of protein starvation must inevitably ensue.

Were we (by ‘we’ is meant the generality of people in this country), to weigh out our food supply, for, say a week, we should soon realise what a large reduction from the usual quantity of food consumed would have to be made, and instead of eating, as is customary, without an appetite, hunger might perhaps once a day make itself felt. There is little doubt but that the health of most people would be vastly improved if food were only eaten when genuine hunger was felt, and the dietary chosen were well balanced, i.e., the proportions of protein, fat, carbohydrates and salts being about 3, 2, 9, 2-3. As aforesaid, the mixed vegetarian dietary is, in general, well-balanced.

While speaking about too much food, it may be pointed out that the function of appetite is to inform us that the body is in need of nutriment. The appetite was intended by Nature for this purpose, yet how few people wait upon appetite! The generality of people eat by time, custom, habit, and sensual desire; not by appetite at all. If we eat when not hungry, and drink when not thirsty, we are doing the body no good but positive harm. The organs of digestion are given work that is unnecessary, thus detracting from the vital force of the body, for there is only a limited amount of potential energy, and if some of this is spent unnecessarily in working the internal organs, it follows that there is less energy for working the muscles or the brain. So that an individual who habitually overfeeds becomes, after a time, easily tired, physically lazy, weak, perhaps if temperamentally predisposed, nervous and hypochondriacal. Moreover, over-eating not only adds to the general wear and tear, thus probably shortening life, but may even result in positive disease, as well as many minor complaints such as constipation, dyspepsia, flatulency, obesity, skin troubles, rheumatism, lethargy, etc.

Just as there is danger in eating too much, so there is much harm done by drinking too much. The evil of stimulating drinks will be spoken of later; at present reference is made only to water and harmless concoctions such as lime-juice, unfermented wines, etc. To drink when thirsty is right and natural; it shows that the blood is concentrated and is in want of fluid. But to drink merely for the pleasure of drinking, or to carry out some insane theory like that of ‘washing out’ the system is positively dangerous. The human body is not a dirty barrel needing swilling out with a hose-pipe. It is a most delicate piece of mechanism, so delicate that the abuse of any of its parts tends to throw the entire system out of order. It is the function of the blood to remove all the waste products from the tissues and to supply the fresh material to take the place of that which has been removed. Swilling the system out with liquid does not in any way accelerate or aid the process, but, on the contrary, retards and impedes it. It dilutes the blood, thus creating an abnormal condition in the circulatory system, and may raise the pressure of blood and dilate the heart. Also it dilutes the secretions which will therefore ’act slowly and inefficiently, and more or less fermentation and putrefaction will meanwhile be going on in the food masses, resulting in the formation of gases, acids, and decomposition products.’

Eating and drinking too much are largely the outcome of sensuality. To see a man eat sensually is to know how great a sensualist he is. Sensualism is a vice which manifests itself in many forms. Poverty has its blessings. It compels abstinence from rich and expensive foods and provides no means for surfeit. Epicurus was not a glutton. Socrates lived on bread and water, as did Sir Isaac Newton. Mental culture is not fostered by gluttony, but gluttony is indulged in at the expense of mental culture. The majority of the world’s greatest men have led comparatively simple lives, and have regarded the body as a temple to be kept pure and holy.

We have now to consider (a) what to eat, (b) when to eat, (c) how to eat. First, then, we will consider the nutritive properties of the common food-stuffs.