Diet is of great importance not only in the treatment of granular kidney, but also much may be done by suitable food to prevent the development of this disease in those prone to it. Further, there can be little doubt that severe as the affection is, life may be prolonged by a suitable dietary in these cases.

Granular kidney affords one of the best illustrations of the principle that the diet should be based not so much on the condition of the urine as on the general state of the patient. Dietetic treatment is peculiarly important in this variety of chronic renal disease owing to the fact that the malady is prone to occur in those who have been accustomed to indulge in the pleasures of the table. Further, granular kidney is peculiarly associated with arterio-sclerosis and cardio-vascular degeneration, and arterial disease would also seem to have a very similar etiology, that is to say, arteriosclerosis and granular kidney may have a common factor in their etiology, although the one is not a necessary and invariable accompaniment of the other.

From the point of view of treatment several different varieties of granular kidney may be recognized. In some cases the patients present obvious renal symptoms similar to those seen in chronic nephritis, but a large proportion of cases come under observation with other symptoms dependent upon the degree of involvement of the cardio-vascular system, or even perhaps with symptoms due to malnutrition.

From the point of view of treatment by diet, perhaps the most important group is that where, with the appearance of health, the occurrence of some symptom as, for example, dyspnoea on exertion, has led to the discovery of the underlying disease. In some cases the disease is discovered purely accidentally as a result, it may be, of a routine examination for life insurance, when the patient has not developed any marked symptoms of ill-health. In these cases, also, much benefit may result from the mode of life being altered and a suitable diet ordered.

In the cases where marked renal symptoms are present and where the patient is more or less seriously ill, the dietetic treatment should be similar to that ordered in chronic or sub-acute nephritis, the degree of restriction depending on the presence or absence of toxic symptoms, gastro-intestinal disturbance, etc.

The dropsy of the so-called cardiac type that is apt to arise in granular kidney, should be treated on the same lines as renal dropsy. There is some risk in cases of granular kidney associated with dropsy of the patient taking or being ordered an excessive quantity of fluid, owing to the large quantities of urine which may be excreted in this disease. The patient often has an exaggerated idea of his renal efficiency, and it must be remembered that although large quantities of water may be excreted, the urine is very poor in solids, and the excretory activity of the kidneys is often notably diminished. It is inadvisable to order these patients, especially if dropsy is present, large quantities of fluid food, as there can be little doubt that hydraemic plethora is thereby increased and better results are often obtained by giving a semi-solid, and therefore, drier food and an allowance of enough fluid to check thirst. No useful purpose is served by undue restriction of the fluids ingested, as dropsy cannot be treated successfully on these lines. In the ordinary case of granular kidney with secondary cardio-vascular changes and where the patient seeks advice, probably owing to the development of cardiac symptoms, and yet where he is not obviously ill, the two main principles of dieting are in the first place to cut down the amount of food, and secondly, to diminish as much as possible the proteins without impairment to the general nutrition.

Granular kidney is a malady especially of the latter half of life, and very often sufferers from it have not with advancing years diminished their intake of food, and they remain large eaters. Hence, very strikingly beneficial results can often be obtained by the mere diminution in the quantity of food.

The amount of fluid consumed requires to be somewhat regulated, but it is difficult to lay down rigid rules with reference to this, as on the one hand it is undesirable to produce hydraemic plethora owing to the high tension which is so often present, and on the other hand, it is advantageous, especially in gouty cases, to give sufficient fluid to procure adequate flushing of the kidneys.

The diminution in the quantity, and especially in the quality, of nitrogenous food taken, the alteration in the character of the food, and especially the substitution, so far as is possible, of vegetable and carbo-hydrate food for the highly nitrogenous animal food, and, thirdly, the judicious administration of diluents are the main principles in the regulation of the diet in these cases.

Although it is essential to cut down the nitrogenous articles of diet, especially meat, it is probably inadvisable to exclude meat altogether, unless complications are present. If the general health be lowered by too rigid and too low a diet there is some risk of producing cardiac dilation and what is usually spoken of as failure of compensation. Many of these patients complain bitterly of the feeling of illness and general weakness produced by too low a diet. It has been the custom to advise, especially in this class of case, replacement of red meat by white meat. It is doubtful, however, whether this is really followed by striking benefit, except in so far as poultry may be more digestible in some instances than ordinary red meat. The main thing to insist on is the regulation of the quantity of meat eaten, and although white meats are poorer in protein than red meat, yet sometimes if the patient be given a free hand, large quantities of white meat may be taken under the idea that it is relatively harmless, whereas better results would be obtained by smaller quantities of ordinary meat of different kinds being allowed. Concentrated meats and preserved, smoked, and salted meats should certainly be forbidden. In the opinion of the writer the best results are obtained by ordering a mixed diet carefully restricted in quantity, and the patient's appetite should be satisfied so far as possible, with vegetables and farinaceous articles of diet. Meat essences, strong animal soups, should certainly be forbidden and replaced by vegetable soups. The quantity of fluid ingested should also be regulated, and especially the taking of large quantities of fluid at any one time. There is considerable risk of increasing the plethora and the blood tension by the sudden ingestion of large quantities of fluid. At the same time it must be remembered that the tension of these patients is necessarily above the normal, and that if it be reduced too suddenly to the normal, serious effects may follow. In other words, regard should be had rather to the condition of the individual patient than to theoretical considerations as to what is the normal pressure, and it must be remembered that such patients have become to some degree accustomed to an abnormally high blood pressure.

Patients with granular kidney not only run dangers from sudden increase of the pressure in the vessels, but it is almost as dangerous for the pressure to undergo sudden diminution. The one effect may be brought about by a too highly stimulating nitrogenous diet with the too frequent ingestion of fluid, and the other danger may result from a too rigid limitation of the diet. It is for these reasons that the diet and the administration of fluids should be regulated to a great extent by the signs and symptoms presented by the patient rather than by any arbitrary rule dependent on the exact height of blood pressure as measured in millimetres of mercury.

Stimulants and condiments of all kinds are inadvisable in these cases, partly on account of their action on the vascular system and partly on account of the very frequent co-existence of gastric and hepatic disorders in such patients. There is not however, the same objection to the taking of salt that exists in cases of chronic nephritis. On the other hand, where the granular kidney is associated with the gouty state, there may be some objection to the taking of large quantities of sodium chloride in the food, as it would seem that this ingredient has some influence on the deposition of urates, and therefore on the production of the gouty paroxysm. Proposals have been made from time to time to replace sodium chloride in the food by salt prepared from vegetables and especially from spinach, in other words, to replace the base sodium by potash (see Gout).

Inasmuch as the excretory activity of the kidney is more or less seriously impaired in cases of granular kidney, it is most important for these patients to avoid all highly-flavoured and elaborately cooked food.