Protein-induced hypercalciuria: a longer term study.

Urine calcium excretion is known to be directly correlated with the level of dietary protein intake. In this experiment we examined the persistence of the hypercalciuria induced by the consumption of high protein diets, and the mechanism of the calciuric response. In a 95-day metabolic study, each of six adult male subjects received formula diets supplying 12 g nitrogen or 36 g nitrogen, and approximately 1400 mg calcium per day. Urine calcium increased rapidly and significantly from an average of 191 mg/day on the 12 g nitrogen diet to 277 mg/day on the 36 g nitrogen diet. There was no significant difference in the apparent absorption of calcium, so that overall calcium balance was -37 mg/day on the 12 g nitrogen diet, and significantly lower at -137 mg/day in subjects consuming the high protein diet. Levels of urinary hydroxyproline, serum insulin, and parathyroid hormone were not significantly increased by high intakes of protein. A decrease in the fractional reabsorption of calcium by the kidney seems to be the most likely cause of the protein-induced hypercalciuria. The consumption of high calcium diets is unlikely to prevent the negative calcium balance and probable bone loss induced by the consumption of high protein diets.