In the dietetic treatment of chronic nephritis we meet with the greatest difficulties because many factors have to be taken into consideration. In the first place the presence or absence of complications such as dropsy, uraemia, and the more serious effects produced by high tension. Secondly, the degree of impairment of the general nutrition as shown by wasting, cachexia, and the presence of anaemia, is a point of the greatest importance. Lastly, the variety of the renal affection that is present and the state of the urine, both as regards quantity, specific gravity, and to some extent the mere amount of albumin present must also receive attention.
The presence of certain complications such as uraemia and secondary inflammations is an indication for a diet similar to that ordered in acute nephritis except that in long-standing cases it is clearly impossible to maintain such a low diet as that ordered in acute nephritis for prolonged periods of time. Still little can be given except milk, gruel, bread, fruit, and possibly in some instances, milk puddings. Animal broths and meat extracts are probably still more inadvisable in this type of case than in acute nephritis. In cases where uraemia, and more especially uraemia of a gastro-intestinal type, is present, the food will probably have to be artificially digested and given in very small quantities. The treatment of these cases, however, is necessarily very unsatisfactory, inasmuch as where uraemia supervenes in chronic renal disease the malady is usually far advanced.
The dietetic treatment of dropsy is more successful than that of the other complications of renal disease just alluded to. Dropsy is seen in chronic nephritis in two main forms. Thus it is a frequent accompaniment of chronic tubular or chronic diffuse nephritis and then has the ordinary characteristics of renal dropsy. In cases of contracted kidney the dropsy is sometimes of a slightly different type and resembles that seen in cardiac disease. From the point of view of diet no distinction need be made between these two varieties. The usual diet ordered for these patients is a milk diet, and not uncommonly they are restricted entirely to milk, which is given in considerable quantities of from 3 to 5 pints a day. There are many arguments in support of such a diet. Thus it is readily digestible in cases where there is no natural disinclination to milk, and in addition many of the constituents of milk have a distinct diuretic action and the flow of urine under such a diet even in advanced chronic renal disease is often materially increased. The percentage amount of albumin in the urine falls and it cannot be denied that many of the symptoms of the disease undergo amelioration and cases are on record where after prolonged administration of such a diet there has been notable improvement. On the other hand there are certain practical and theoretical objections to such a diet being ordered as a matter of routine in all cases of chronic renal disease accompanied by dropsy. In the first place, many patients are very intolerant and dislike an exclusive milk diet, and this perhaps is especially the case in those instances of chronic renal disease where there may be much nausea and anorexia and dislike to all food. Again, it is difficult to maintain the body-weight and the normal nutrition in an adult on a milk diet for a prolonged period. Such food is unduly rich in protein and contains insufficient carbo-hydrate and fatty materials and theoretically an excessive protein diet is unsuitable for chronic renal disease. Further, where large quantities of milk are taken there must be considerable risk of producing hydraemic plethora and thus there may be a danger of aggravating any existing dropsy. All these objections are of considerable force and there is another dependent on the richness of milk in saline ingredients and thus there is the further danger of aggravating the dropsy owing to the retention of sodium chloride if the elimination of this by the kidneys is deficient. The risk of milk containing an excess of protein matter loses some of its force, owing to the loss of albumin, and hence the waste of protein matter that is such a constant accompaniment of chronic nephritis accompanied with dropsy. Although some patients with chronic renal disease improve under milk diet there can be no question that a very large number do not and that notwithstanding the increase in the flow of urine, and the diminution in the percentage amount of albumin present, there is no real improvement when the patient is tested either by his own feelings or by the state of the general nutrition. As already mentioned above the diminution in the albuminuria is often more apparent than real owing to the increased flow of urine resulting from the fluid ingested. This fallacy of observation is one of the reasons why attention should be directed to the general condition of the patient rather than to the mere analysis of the urine alone. It is probable that an exclusive milk diet is mainly of service in chronic nephritis where complications are present or where there is reason to think that sub-acute nephritis is superadded to the chronic disease.
Where no complications are present it is probable that better results can be attained by a modified diet containing larger quantities of carbo-hydrates and for this purpose farinaceous foods prepared with milk may be given with advantage such as bread, corn-flour, rice, etc.
The question of more fundamental importance, however, is whether better results cannot be obtained in cases where dropsy is present by the administration of a drier food and also by restriction in the ingestion of sodium chloride. Some striking results have been obtained, especially in France, in the treatment of chronic renal disease by the administration of a diet containing considerable quantities of vegetables prepared and cooked and taken without salt. In many such cases there is really no objection to the giving of eggs, although there is much prejudice against this article of diet in renal disease. Egg albumen is readily digestible and very large quantities must be taken in order to produce any irritating effect on the kidney, and the albuminuria that results from the indiscriminate administration of raw eggs is an albuminuria apparently produced by a toxic action on the renal structures. It may therefore be advisable in chronic nephritis accompanied by dropsy to replace an exclusive milk diet by one consisting of bread and milk, eggs, arrowroot, rice milk, and vegetables plainly cooked without salt. In some instances milk may be omitted altogether and the diet consist of farinaceous food-stuffs, vegetables and one or two eggs in the twenty-four hours.