American Journal of Clinical Nutrition, Vol 4, 466-481, Copyright © 1956 by The American Society for Clinical Nutrition, Inc.

The Effects of Diet on Renal Function In Healthy Men

¹ From Health Service Research Unit, University of Illinois, Urbana. Supported by USAF Contract AF 18(600)-80

Observations on renal function have been collected in 8698 subject-days in 211 healthy young men. Strict control of diet, fluid intake, and daily activity were maintained continuously. Temperate, cold, and hot environmental conditions were included. Three categories of observations of renal function were made : (1) standard qualitative and morphologic procedures, (2) standard quantitative tests, and (3) nonstandard studies of water and osmotic regulation. Many alterations can be provoked in renal function by nutritional imbalance, caloric deficit, dehydration, physical work, and extremes of temperature.

Glycosuria is extremely rare. Ketonuria is easily produced by nutritional imbalance, exposure to cold, or hard work. Transient albuminuria may be produced by an unbalanced diet or vigorous exercise, and exposure to cold accentuates this phenomenon. Microscopic hematuria and cylindruria may be produced by unbalanced diets, especially pure carbohydrate or starvation. When a predisposition exists, moderate exercise may accentuate the microscopic hematuria and cylindruria.

A combination of chronic dehydration and a diet containing over 12 grams of nitrogen per day increases the concentrations of urea, creatinine, and nonprotein nitrogen in the serum. Caloric deficiency decreases creatinine and urea clearances. Gross variations in diet can produce large alterations in the clearance values for sodium, chloride, and total osmolar active substances.

In these investigations the experiments involved all possible combinations of water deprivation, salt deprivation, and protein deprivation, thus producing the three commonly recognized varieties of hydropenia; i.e., pure water depletion hydropenia, pure salt depletion hydropenia, and mixed salt and water hydropenia. In the chronically and severely dehydrated subject an ingested water load is retained only when the osmolar excretion exceeds 700 milliosmols/day. Therefore, without knowledge of the rate of osmolar excretion, one cannot conclude that a subject is well-hydrated merely because he excretes a copious volume of dilute urine after a water load.

Our data from healthy young men have been generalized into a single equation in which the parameters, osmotic load, obligatory urine volume, and isosmotic urine volume, are interrelated. The maximum possible concentrating capacity of the kidney is reached at a urine/serum osmolar ratio of 5.22. Osmotic load is an important consideration in any study of osmotic and water regulation and clearance.

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