In health the kidneys extract from the blood the excess of water, and the products of nitrogenous waste - urea, uric acid, etc. There is a definite relation between the quantity and quality of food ingested and the state of the urine. Thus a concentrated dry diet diminishes the amount of urine and renders it more acid; a liquid diet, e.g. milk, has diuretic properties, increasing the amount of urine voided. Animal foods and the more highly nitrogenous vegetable foods increase the amount of nitrogenous waste products in the urine, and also increase its acidity. Vegetable foods, on the other hand, lead to an increase in the salts of the urine; they tend to make it less acid, or even alkaline in reaction. A dry diet, and one which contains a high proportion of protein, throws a greater strain on the kidneys than one which contains much fluid and in which the proportion of protein foods is small in amount (see Appendix, p. 578). Advantage is taken of these facts in the treatment of nephritis and other kidney disorders, the indications in treatment being - (a) to lessen the amount of work thrown upon the kidneys; this is effected by diminishing the proteins, and especially the animal proteins, in the food; (b) to avoid articles of food which during their excretion may irritate the diseased organs, such as alcohol in all its forms, spices, ginger, and the like; (c) to maintain a permanent modification of the diet along these two lines from the time that the existence of renal disease has been detected.
It must be borne in mind that many cases of acute nephritis are not examples of a primary inflammation occurring in a previously healthy organ, but are really examples of an acute inflammation supervening in a patient who was previously the subject of subacute or chronic nephritis. It is important to recognise this, because care must be taken in all cases of chronic nephritis associated with an acute exacerbation of inflammation not to lessen the general strength of the patient by keeping him for too prolonged a period on an unduly restricted dietary. The dietetic treatment of acute nephritis varies slightly according to the type of the disease, more especially as to the presence and severity of general dropsy. Attention will first be directed to the treatment of a simple, uncomplicated case of a primary acute nephritis, such as is associated with not more than a slight degree of cedema of the tissues.
In sthenic individuals all food should be withheld for the first twenty-four or thirty-six hours, during which diluents may be given in the form of plain water, potash or soda water, Salutaris, or Apollinaris water, to the extent of from 2 to 4 pints in the twenty-four hours. Barley-water, rice-water, or toast-water may be substituted if desired. Thereafter the diet should consist exclusively of milk, from 1 to 3 pints, increasing, it maybe, up to 4 or 5 pints, in the twenty-four hours, diluted with an equal amount of water as above. In cases where milk is not readily digested, whey may be substituted with advantage, and, similarly, 1 pint or more of buttermilk in the twenty-four hours may advantageously replace an equal quantity of milk, the buttermilk allaying the thirst and improving the state of the digestive tract. The milk is more easily digested when administered in small quantities, eg. from 8 to 10 ounces every one and a half hours. If there is difficulty with the digestion of milk, it may be given pepton-ised or pancreatised. As the general condition of the patient and the state of the urine improves, the milk may be reduced in amount and its nutritive value increased by the addition of Benger's food, Allenbury diet, Horlick's malted milk, Plasmon, or similar preparation; and, later, by the addition of bread and butter, milk puddings, fruits, and green tables, with, if desired, a cup of tea. Meat in the form of fish, chicken, tripe, or sweetbread may be added to the diet, usually about the fourth week, and may be continued, provided its use is not followed by an exacerbation of symptoms - oedema, albuminuria, haematuria. Various otable soups, such as tomato soup, lentil or pea soup, are also useful at this period. A full ordinary diet should not be allowed for at least a month after the complete disappearance of albuminuria from the urine.
Here the amount of food and drink should be restricted to the smallest possible quantity, e.g., from 2 to 3 pints daily of milk diluted with carbonated water. Buttermilk may be substituted with advantage. This regime should be kept up for four or five days, by which time, in favourable cases, an improvement in the condition of the patient will allow of the treatment laid down in the preceding paragraphs.
Some patients show a marked intolerance for an exclusive milk diet, and for these the fermented milks, koumiss or Kephir, may be recommended. Such patients may be able to take buttermilk, whey, or various pancreatised preparations in place of ordinary milk. The addition of rice-water, barley-water, or oatmeal-water to the dietary promotes the toleration of a milk regime, and, in the same way, the administration of an imperial drink is of service. The constipating effects of a milk diet may be counteracted by the use of Philp's milk of magnesia, or Dinneford's fluid magnesia, or plain citrate or sulphate of magnesia. Any tendency to diarrhoea may be checked by the addition of lime-water.