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Long-Term Effects of Excess Protein and Phosphorus on Bone Homeostasis in Adult Mice^1,2,

Department of Nutrition, College of Biological Science, University of Guelph, Guelph, Ontario, Canada N1G 2W1

In adult human subjects, an interaction between dietary protein and phosphorus has been reported, in which the hypercalciuric effect of excess protein is counteracted by the hypocalciuric effect of phosphorus, with restoration of calcium balance. In adult rodents, bone homeostasis is maintained over a wide range of protein intakes, whereas high phosphorus diets cause bone loss, despite their hypocalciuric effect, as the result of an overriding increase in the excretion of endogenous fecal calcium. The present study was designed to determine whether there is an interaction between dietary protein and phosphorus with respect to bone homeostasis in adult mice. Four-month-old ⁴⁵Ca-labeled B6D2F1 female mice were fed for 52 weeks the following diets (in percent): control, Ca, 0.6; P, 0.3; protein, 15; high P, Ca, 0.6; P, 1.2; protein, 15; high protein, Ca, 0.6; P, 0.3; protein, 30; and high P + high protein, Ca, 0.6; P, 1.2; protein, 30. Urinary calcium was persistently increased in the high protein group, depressed in the high P group and transiently depressed in the high P + high protein group. Excess dietary protein prevented phosphorus-induced kidney calcinosis. ⁴⁵Ca loss was increased in the high P groups, but not in the high protein group. There were significant decreases in the mass of the femurs and tibias in both high P groups, whereas there was no effect of high protein intake. These results show that bone homeostasis in adult mice is sensitive to excess dietary phosphorus but not to excess protein, and that there is no interaction between these nutrients with respect to their effects on bone.

KEY WORDS: • phosphorus • calcium • bone homeostasis • protein

¹ Supported by the Natural Sciences and Engineering Research Council of Canada.

² Presented in part at The Fourth Joint Meeting of AIN, ASCN and CSNS, University Park, Pennsylvania, July 22–24, 1982. Yuen, D. E. and Draper, H. H. (1982) Long term effects of excess protein and phosphorus on bone homeostasis in adult mice. J. Nutr. 112(6). xxvi (abs).

³ To whom reprint requests should be sent.

Manuscript received 22 December 1982.