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 adequately insalivated.
A moderate diet is one just sufficient (supposing the various food-stuffs - 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, bird, 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.
All through life starchy foods should, as far as possible, be taken in a form compelling thorough mastication. Soft starchy foods, such as puddings, are only admissible on condition that they be thoroughly masticated.
It is worthy of note that the diet of early man conformed to these three requirements. It was simple, consisting as it did of unprepared animal and vegetable substances; the quantity was not on the whole in excess of physiological needs; and all the starchy food being raw, it had to be abundantly masticated in order to break up the non-digestible cellulose framework and thus liberate the contained food-stuffs.
When we come to compare the ideal with the actual in the present day, the contrast is sufficiently discouraging. Too often stomach and bowel are burdened with an excess of food, and harassed by a too great variety of it. Efficient digestion is rarely possible under these circumstances, and consequently the blood is surcharged with nutrient matter, much of which is in an imperfectly digested form. The tissues being thus bathed in an over-rich and perverted plasma, metabolism fails to proceed normally, and health suffers.
In order to show the application of these remarks to the subject in hand, it may be well briefly to survey the changes which the food undergoes in its passage through the body. These changes may. be considered under three phases : digestion (i.e. the conversion of the ingested food into nutrient plasma), metabolism (i.e. the nutritive changes which the absorbed food undergoes in the tissues), and excretion (i.e. the removal of waste-products).
These three functions, as we may term them, are most vigorous in youth and early adult life. Then it is that digestion is most vigorous, metabolism most active, and excretion most efficient. At forty, or thereabouts, the digestive function often begins to show signs of failure, and greater care has to be exercised in the selection of food than was before necessary. Apart from this there is now a greater disposition to prudence - the recklessness of youth tends to depart with maturer years. Young people who have unrestricted choice of luxurious foods are very apt to upset themselves: the "stomach-ache" of Christmas time is as proverbial as the "dose" which follows it. This dietetic imprudence may survive childhood, adolescence, early adult life, nay, it may persist into old age, but most people have acquired some sort of dietetic wisdom by the time they have reached middle age.
At this period not only does digestion often begin to lose its former vigour, but metabolism also shows signs of flagging; the vital fire no longer blazes as it did in the days of youth. Consequently the products of katabolism are not burnt off as readily as they used to be, and if excretion is defective they may accumulate and cause trouble. As yet, however, excretory activity does not show any decided signs of waning.
With the gradual onset of old age there is a further waning of digestive and metabolic activity, in consequence of the degenerative changes which are set up in the tissues. With the digestive organs showing an appreciable increase in their fibrous elements and a corresponding atrophy of their epithelium, it is not surprising that digestion should lack its early vigour. Similar changes are observed throughout the tissues generally, and there is a corresponding sluggishness of metabolism - the vital fire, which has long since ceased to blaze, now smoulders feebly, less oxygen is absorbed and less carbonic acid given off. Except in the case of definite disease of the excretory organs, it is doubtful whether the aged suffer in any marked degree from their inefficiency..
Inasmuch as after early adult life there is a steady waning in the ability of the organism to digest and metabolise the food taken, it follows that the need to conform to the requirements of the ideal dietary becomes with advancing years increasingly pressing. In early life the majority of people can cope with a dietary which departs widely from the ideal - they are able to consume with comparative impunity not only far more food than is required, but also all sorts of foods which in later years cannot be tolerated. We say with "comparative impunity," because chronic dietetic delinquencies, even in early life, cannot but be harmful in the long run, although an occasional lapse from a severely correct diet may, in the case of the habitually abstemious, be actually beneficial, and this even after middle life.
Respecting the capacity of the organism to cope with different kinds of food, the influence of custom and of idiosyncrasy, as well as of age, has to be reckoned with.
As to the first of these influences - while one should be cautious in recommending to an aged person a diet very different from that to which he has for many years been accustomed, the experience derived from prisons, workhouses, and similar institutions shows that the ability of the aged to adapt themselves to novel kinds of diet is by no means small. It is, indeed, astonishing what can be achieved in this direction if the necessary pressure can be brought to bear. Unfortunately in private practice this is not often possible, but if we can only secure his co-operation we may often succeed in getting an aged person to tolerate a dietary very different from that to which he has accustomed himself.