On The Value And Digestibility Of Foods
( Originally Published 1912 )
As our whole life and well-being depend on the proper digestion of our food—air and water, the two other necessities of life, fortunately needing no such elaborate process of absorption—the management and choice of our food becomes a matter of the greatest importance.
It would seem to the casual observer that, in youth especially, we can afford to make foolish experiments and mistakes in our diet, to go too long fasting, to take far too much at one time, and to eat the most incongruous mixtures; for in a day or two we seem to be all right again. Our animal economy is, luckily for us, so wonderfully made and planned that it is able to meet almost all demands and emergencies in the way of food, and to get rid of the resulting waste and poisons; but this is not strictly true. Every excess in eating and drinking, every unnatural call on our digestive powers, leaves some mark, invisible perhaps, on our reserve of power. We vary, of course, as individuals, enormously in our powers of assimilation, and in the immediate penalties we have to pay for our mistakes; but that is a reason why each man should find out his personal equation, and so in early life, while recuperation is the law, learn the lessons of self-denial and self-management. The man who can commit excesses apparently with impunity, the man who boasts that he has never had a day's indigestion in his life, comes to grief in the end long before his proper time. It would seem that our wise Creator has planned us for imperfection rather than for perfection, but in reality that we should attain perfection through the lessons and sufferings of our imperfections.
As our years advance we can still less afford to make mistakes, for we recover more slowly or not at all, and our excretory organs, that clear away our rubbish-heaps, are not up to any new or additional strain of work. Hence come gout, rheumatic affections, kidney disease, and nearly all the troubles of old age.
The problem is not, perhaps, so much the food, as we grow older, but the quantity. Many of us, in old age, improve in our digestions; foods that used to make us bilious, for instance, we can often digest quite well. The man or woman, the sufferer from sick-headaches and migraine, generally loses them after or before sixty. It is difficult to explain this, but it is partly due to lessened nerve-strain.
Let us briefly consider the whole progress of digestion. It begins in the choice of food; it then belongs to the kitchen or the cook. If we can control these first two problems, we come to our bodies. The first and very important question arises, Can we masticate our food? As we grow older our teeth generally become less perfect in their work, and it is here that a good dentist can do so much to help us. But how often we avoid him and put off the evil day ! Though we may have lost a tooth here and there, we say we have a good lot left, but a healthy tooth without a vis-a-vis in the opposite jaw is dancing a pas seul. It may be an interesting performance for the tooth, but its original purpose, that of a grinder, is not being fulfilled. In fact, many old people do better with no teeth at all, than with some here and there that do not meet. The toothless gum often becomes in time a fairly efficient masticator, but its food, of course, needs common-sense selection. The imperfect mastication and pulping of our food means necessarily the imperfect mixing of that food with the saliva; the saliva is not merely a lubricant, but is the first agent in the chemical process of digestion, for it transforms the starch of our food into something that can be absorbed. Imperfect mastication means, also, that the food is swallowed more or less in lumps, and so gets imperfectly mixed with the gastric juice in the stomach.
Sir Andrew Clark's dictum was this in reference to the importance of good mastication : " Thirty-two teeth in one mouth, thirty-two bites to every mouthful, and for any tooth that is gone the number of bites to be proportionately increased." The knife and fork can be made to do much of the work of the teeth, but they do not supply the saliva. Here one must say a word on the variation of one's diet. If our stomachs were like a big test-tube, into which we put certain ingredients and apply to them certain chemical agents at a certain temperature, the process of digestion would be shown by a mere chemical formula; but the chemical agents that do our work are not always on tap, or they vary in amount and in strength. They are produced in answer to the calls of our nervous system, and are not mere automatic productions. Thus it is that appetizing food and the smell of well-cooked food acting through our nerves cause a good supply of saliva our mouths and of the gastric juices in our stomachs.
This explains the value of wholesome condiments such as salt, mustard, and pepper, and the different effects of well or badly cooked food. Monotony in diet has a dulling effect on the nerves that govern our digestions, just as continual sameness has on our lives generally. We may design a perfect diet from a chemical point of view, but the monotony of it will cause it to disagree in time. One may live on mutton-chops and rice-pudding and feel that one has a lump of lead in one's side, and one may then go out in pleasant, cheering company and eat one's way steadily through a dinner of many and varied courses, and digest it perfectly, and in the end feel all the better for it.
Our nature seems to crave for change, and our stomachs seem the better occasionally even for a shock. Enjoyment of food is not essential for digestion, but is a great help.
In support of this argument for change, one can-not help telling the story of the Eton boy who had to write an essay on the ancient Greeks (the humor was of course unconscious). He said : " The custom that a man should have only one wife was first instituted by the Greeks ; they called it monotony."
This dependence of our digestive powers on our nervous system points also to other things, to the importance of not coming to our meals in a state of nervous or physical exhaustion. Many an elderly person does far better with a rest before food and after, and not distracting his nerve powers by reading continually while eating. Anxiety, grief, and trouble, as we know to our cost, affect our digestions, but they are often outside our control
When we have swallowed our food, the digestion by the gastric juice begins; this process lasts for varying times, according to the nature of the food, but it always needs time for its work, and it should not be hurried. It is a mistake to eat one course too quickly on the top of another, and it is a mistake also to start the busy actions of life till the digestion is well on its way. The busy man should make his chief meal when his work is done, while the idle man had better, perhaps, make it in the middle of the day. This last applies particularly to old people, for at that time they have more nerve energy, and their sleep at night is better for not having partially digested food in their stomachs, Really old people do better, I think, with little or no animal food in the evening. The breakfast and the early dinner should be their important meals.
The question of the nature or constituents of our diet in old age is a very important one. Clearly by nature man was formed for a mixed diet, and old age should continue it, but with variations and discretion. As I have said in my first chapter, the quantity of one's food should be regulated in a measure by the mental and bodily work we do, and in healthy old age a wise quantity is of more importance than quality; there is no reason why we should not eat a moderate quantity of meat, but if there is a tendency to arterial disease, to thickening of our arteries, and to abnormally increased blood-pressure, then meat should be very sparingly taken, and that not every day. Beef, pork, and veal are more injurious probably than mutton and lamb. Here the diet should certainly be in the direction of the vegetarian, with the supplement of eggs, but-ter, cheese, and wholesome white fish, such as soles, plaice, whiting, flounders, and brill. Salmon and mackerel are probably rather injurious.
Of the vegetable foods the pulses, in such cases, such as beans and peas, are not so suitable as the cereals. Old folks who are knocked off their meat eat as a rule too little fat; there is very little fat in fish or in birds, but with red meat the fat is so mixed up with the muscular fibres or lean, that they eat a good deal without knowing it. This want of fat is best supplied by good bacon, hot or cold. Many of us certainly know from experience that cold boiled bacon, especially in winter, is the wholesomost form of animal food that we can find. Dr. Harry Campbell says this : " The ideal dietary, the most suitable diet for the aged, is that which constitutes the ideal diet for man in general. Such a dietary demands (a) moderation in quantity, (b) simplicity in quality, and (c) the avoidance of those starchy foods which are apt to slip into the stomach without having been first well mixed with the saliva.
"A moderate diet is one just sufficient (supposing the various foodstuffs, fats, proteins, etc., to be properly balanced) to maintain a person at the lightest weight consistent with the most perfect health of which he is capable. It is manifest that any food over and above this sufficiency can do no good and may do harm.
" By a simple diet is meant one consisting of such items as bread, plain biscuits, plain puddings, plainly cooked vegetables, fruit, meat, fish (all plainly cooked), milk, butter, cheese (such as cheddar), tea, coffee, cocoa, salt. Dishes calculated to tickle the palate are not included in the simple diet. A simple diet excludes alcohol and all condiments other than salt and occasionally pepper and mustard.
" Avoidance of soft starchy foods. All through life starchy foods should be taken, as far as possible, in a form compelling thorough mastication."
The indigestibility of starchy foods is, in a measure, overcome by the use of well-made malted or predigested foods.
The scientific study of diet has shown that certain quantities are necessary for the maintaining of life; these foods and quantities represent a minimum, but the difficult problem is to find out how much food, and `what is necessary for the maintenance of life in its fullest activity, so that the greatest output of work can be obtained. The overstepping of this amount, when long continued, leads inevitably to disease; the diminution leads also inevitably to debility and inefficiency.
These quantities, etc., have been worked out into what are called " calories." Roughly a small calorie is the amount of heat required to raise a gramme of water through I ° Centigrade, and the large calorie (Which is used now in most books on this subject) is a thousand small calories. This is no place for a complete scientific explanation of this subject, but briefly stated, " the caloric value of any food can be determined by a calorimeter, and is a measure of the energy which is given out by the complete oxidation of the substance." The above is a quotation from Dr. Spriggs' article in " A System of Diet and Dietetics," edited by Dr. G. A. Sutherland, and what follows is also from the same article :
" We have seen that the common experience of mankind and the evidence of scientific inquiry agree that a sufficient amount of food must be taken daily to yield from 2,500 to 3,000 calories. When we come to inquire of what constituents this food should consist, we find a general agreement upon fundamental points, but a great deal of difference of opinion upon others. It is established that the dietary of man should include all three food-stuffs, protein, fat, and carbohydrate. The protein is essential: no other material can supply the loss involved in the wear and, tear of living organs. No other food-stuff can entirely supply the needs of an animal as protein can those of the carnivora. In the case of man, a healthy existence cannot be supported upon protein without carbohydrate, and it is a great advantage to him to have fat in his diet as well, since fat gives a greater proportion of energy, weight for weight, than carbohydrate or protein. We have seen that protein furnishes material for the metabolism of structure, whilst carbohydrate and fat, and any protein in excess of that required for structure, furnish energy for the metabolism of function, or put in another way, fuel value to supply heat and work. Two points arise for consideration : first, What is the minimum amount of protein which is essential for existence? and secondly, What is the amount which is desirable in order to maintain the body in the highest degree of efficiency? The first question we can answer upon the evidence before us, but there is considerable disagreement on the second. Provided that a certain minimum of protein be supplied, and sufficient caloric value, an active life can be sup-ported upon very varying proportions of the three elements. This fact must be clearly borne in mind. Any experiments showing that men can live and work for long periods upon this diet or upon that, provided that the constituents satisfy the above fundamental condition, show us nothing new. Men have existed in the past, in the vicissitudes of wealth and poverty, freedom and captivity, upon dietaries as varied in both quantity and quality as will ever be designed by experimentalists. The main object of our inquiry must therefore be not to determine upon how much or how little a man can live, but what are the proportions of the food-stuffs upon which he can live with the greatest efficiency and economy."
It must be evident that, as our work lessens and our age increases, a less amount of food than the full work average will be needed, and we must remember that the quantity of food must bear some relation to the weight of the body. In the above quotation protein (often known as albumen) is contained in all animal foods, in eggs, and in smaller proportion in cereals and pulses.
That the protein is derived from the animal or vegetable source is not of much consequence.
The carbohydrates are represented by what we call starchy foods, such as vegetables, cereals, pulses, and sugar; and the fats are the fats of meats, but-ter, animal-oils derived chiefly from fish, and to a lesser extent vegetable oils, as olive oil. The amount of protein required varies a good deal with the nature of the work demanded.
The consideration of the principles on which diets are constructed has led us to the following proportions of food-stuffs for a man of 11 stone, leading a life of moderate activity:
Protein 100 grammes= 410 calories.
Total heat value...=2,820
This is almost exactly given by bread, 1 lb.; meat, 4 ounces; eggs, 4 ounces (two small ones) ; cheese, 2 ounces; potatoes, 1 lb.; butter or other fat, 2 ounces ; milk, 1/4 pint ; sugar, 1/2 ounce.
For a man or woman of 9 1/2 stone an adequate supply would be, bread, 12 ounces; meat, 6 ounces; potatoes, 1/2 lb.; butter, 1 ounce; milk, 1 pint ; sugar, 1 ounce ; milk-pudding, 8 ounces ; soup, 1 pint.
This is the ordinary diet of St. George's Hospital, and contains protein, 90; fat, 75; carbohydrate, 330; calories, 2,400; and is designed and is sufficient for those doing no work.
Dr. Spriggs says in conclusion that we may adopt Atwater's standard as embodying the results of modern investigations into the diet of adults:
For women with light muscular work 90 2,400
As we get on in life it will not be difficult from the foregoing tables to construct a diet which, while giving changes, will approximately supply all we need, and which will not by excess of one or other constituent put too great a strain on our organs of elimination, such as the kidneys. The amounts of food needed will, of course, vary not so much with the number of one's years as with the muscular work, in the shape of exercise that we are able to take.
The tables by Dr. Spriggs (page 58) classify the common foods according as their energy-giving is due to protein, carbohydrate, or fat. It will be noticed that milk is the only food in the lists which contains a good proportion of all three. Cheese, Brazil nuts, and bread, are represented in each list and contain a fair proportion of at least two of the food-stuffs.
For experimental purposes these foods were tested singly, but in an ordinary mixed diet the problem becomes a good deal more complicated. The admixture of some foods will probably hasten digestion, while that of others may hinder it; these gastronomic peculiarities and vagaries are discoverable only by personal and often bitter experiences.
If we take, for instance, the figures of lean beef in the first and second columns—viz.,
Lean beef 90+10, we get its value.
By roughly arranging foods according to such a table, we can arrive at the proper balance of its various constituents.
Again I must remind my readers that the chemical side of the problem is not the only one to study. Idiosyncrasy, appetite for certain foods, distaste for others, and personal experience, must all enter into the question. The appetite for certain foods varies much at different periods of life. Fat, for instance, is abhorrent to many children, and their lives and digestions are made miserable by the parental but unscientific command to " clear up their plates."
In later years the same person will often welcome fat and need it. Sugar, again, is loved by children, scorned often by middle age, which supplies its place partly by wine and beer, and is again welcome and often very useful in old age, for it helps much to keep up the failing heat of the body. In hearts that are growing old and feeble good cane-sugar is a direct food for the weakening muscle of that most important organ. Plain sugar added to food or drink is more digestible, I think, than sugar in the form of preserves—the latter is more likely to turn acid.
The digestibility of food is not governed necessarily by its chemical composition, and here our own experience, again, and that of others should be a guide. There is as much nourishing material in twice-cooked as in once-cooked meat, but most people digest it with far more difficulty, and one does not get as much nourishment out of a food that one's stomach manages badly, for there are certainly more waste products produced which are never absorbed.
The digestibility of new and stale bread varies much with most people, but the contents, of course, are the same chemically. Hot fat and cold fat, again, differ much in their wholesomeness. To many hot fat is too rich and makes them bilious; while cold fat agrees perfectly. We see this particularly in the use of hot and cold bacon.
All these things we must study and observe each man for himself, and we must not let our likes and our appetites influence and sway the conclusions of our knowledge and of our personal experience.