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Effects of high protein diet on water metabolism and on various renal functions were studied in 4 medical students. The daily water intake during the high protein intake was averaged to 3,000ml of which 39% was from liquids, 49% from the water contained in food and 12% from the water of oxidation. Of the daily water output, 53% was by urine, 3% by feces and 44% by the evaporation. As compared to the occidental, this average daily water intake of 3,000ml on high protein diet was greater in the Korean. Moreover, the daily water intake for a given caloric intake or body weight was still significantly greater in the Korean. Moreover, the quantitative pattern of daily water exchange was not modified by the protein content in the diet. On the other hand, the urine osmolarity as well as the urea concentration increased when the protein intake was augmented. However, the urinary concentrations of Na+, Cl- and K+ were not affected by the amount of protein intake. When high protein diet was given, the values of CIN and CPAH showed only a slight increase but renal concentrating ability as judged by the magnitude of maximal negative free water clearance (TcmH20) showed a significant increase. From these results, it is evident that the lower renal concetrating ability of the normal Korean is most likely due to low protein intake. However, greater water intake in the Korean is independent of the changes in the renal concentrating ability. On the basis of these facts, it is again suggested that greater water intake in the Korean is attributable to greater salt intake.
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