Effects of excess protein, sodium and potassium on acute and chronic urinary calcium excretion in young women

The extent to which chronic calciuric effects of excess protein, sodium and potassium were reflected in fasting and acute urinary excretion was determined in 10 healthy premenopausal women. Chronic excretion was measure after one week of stabilization to a high protein (HP) diet by adding 50 g protein (casein and lactalbumin, 80:20) to subjects' usual diets. Then, randomly, subjects received each of the following treatments added to a constant baseline diet in Weeks 2-4: HP, HP + 70 mmol KHCO₃ (HP+K), and HP (as casein only) + 70 mmol NaCl (HP+NA). In Week 5 subjects received the moderate protein (MP) treatment in which 50 g carbohydrate was given. Subjects provided 24-hour urine on Days 3 and 4 each week. Fasting blood and urine were obtained the morning of Day 5, after which the acute load study began. Subjects ate meals containing one-third (1/3) of the respective treatment, followed by collection of timed urine and blood samples. In the chronic load study, calcium excretion was highest with Hp+na compared to Mp and was intermediate with HP or HP+K treatment. Sodium and potassium excretion were reflective of the dietary intake. Net acid excretion was lowest when subjects were given added KHCO₃. Sulfate and phosphate excretion were highest during all of the HP treatments. Fasting sodium and calcium excretions were higher after chronic HP+Na or MP treatment compared to lip and HP+K. Acutely, incremental calcium excretion was higher for 1/3HP+Na and also 1/3MP. There was no hypercalciuria due to protein, nor hypocalciuria due to potassium. There was a modest hypercalciuric effect of sodium chloride. Comparing chronic effects to acute effects in this study of acclimated subjects, and to acute effects in unacclimated subjects from a previous study, similarities were observed. Thus acclimating subjects to treatment offers no benefit for studying diet-related effects on calcium excretion except to demonstrate a hypercalciuric effect of sodium chloride.