THE EFFECT OF ANTECEDENT DIET ON URINE CONCENTRATING ABILITY

Abstract

Thirty-six concentration tests were performed on 9 subjects after they had received 1 of 4 liquid diets for 3 days. The highest concentrations were achieved following the diet high in protein, and the in-crease over the concentration achieved by the same subjects on a diet low in protein was as much as 0.014 specific gravity units. This superiority of high-protein diets was still apparent when the degree of dehydration was increased. Four measures of concentration were employed. The weight of the dried solids was used as the standard of reference for physical concentration of urine. In this measurement the refractometer proved to be superior to osmometry or specific gravity measurement. However, osmolar concentration is a more physiologic measurement of the concentrating power of the kidney, and in this measurement specific gravity proved to be superior to total solids or re-fractometry. Regardless of which measurement is used, it cannot be interpreted unless it is known whether the principal solute in the urine is salt or urea. The simplest measurement is specific gravity, and a practical way to cause the urine to be rich in urea is to give a high-protein diet before the concentration test is performed.