Various types of functional albuminuria have been recognized in the past and attributed to different causes, such as exertion, cold bathing, dietetic causes, and the most important of all, that dependent on the assumption of the erect posture, also called the postural or orthostatic variety. Of late years more importance has been attributed to posture as a cause than to diet, and certainly in most cases of functional albuminuria, and especially in those with well-marked postural characteristics, diet has little or no effect in influencing the degree of albuminuria. In postural cases albuminuria disappears when the patient is put in the recumbent posture even when the diet is not restricted, and such albuminuria may disappear within half an hour of the assumption of the recumbent posture. On the other hand, certain articles of diet if taken in great abundance, more especially eggs in a raw state, may give rise to albuminuria, and hence it is impossible, perhaps, to exclude dietetic causes as an occasional cause of some varieties of functional albuminuria; nevertheless, diet is not an important cause of the common form of functional or postural albuminuria seen in adolescence. Further, it must be remembered that some constituents of the urine present in abnormal quantity may apparently irritate the kidneys and lead to slight albuminuria; thus traces of albumin may be found associated with oxaluria and excess of uric acid, or the excretion of urates in an abnormal form, as, for instance, the spicular crystals of acid ammonium urate. Albuminuria dependent on these causes may require dietetic treatment to restrict the output of oxalates or of uric acid, but in the ordinary cases of functional albuminuria little benefit is to be expected from dietetic measures, and certainly the low diet suitable for certain forms of nephritis is quite inapplicable to such cases.
The principles of diet in other renal affections, such as cystic kidney, tuberculous disease, pyelo-nephritis are much the same as those applicable to nephritis, but in some of these conditions, especially where pyelitis is present, attention should be directed to the reaction of the urine, as much of the discomfort produced by frequent micturition may be relieved by ordering a diet rich in vegetable matter so as to render the urine less acid. In most of these other renal affections, the general condition of the patient should be an important factor in determining the diet. Thus in tuberculous kidney, it may be far more important to diet the patient from the general point of view of tuberculosis rather than from the point of view of the urinary changes. In such a malady, although the urine may contain considerable quantities of pus and albumin, yet large areas of renal substance may exist in a more or less healthy condition, and the renal efficiency of the patient may not be seriously impaired, and thus there may be no real necessity for limiting the quantity of food taken. Similarly in cases of cystic kidney, although the urine excreted may be dilute, still in many cases, a considerable amount of healthy renal substance is still present. On the other hand, in some cases of cystic kidney the renal tissue between the cysts has become fibroid, and such patients present signs and symptoms similar to those of granular kidney, thickening of the vessels, cardiac hypertrophy, with high tension being also present. When this is the case dietetic treatment similar to that suitable for granular kidney should be ordered, and probably in all cases of cystic kidney, owing to the dilute character of the urine excreted, it is wise to limit the nitrogenous ingesta to some degree.