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Effect of Chronic High Protein Feeding on Bone Composition in the Adult Rat^1,2,

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

A study of the effect of feeding a high protein diet on bone metabolism was conducted using adult rats deep-labeled with ⁴⁵Ca. A control diet (15% soy protein plus 0.2% methionine) and a high protein diet (control plus 20% lactalbumin) were fed for 10 months. Rats fed the high protein diet exhibited increases in urinary Ca, ⁴⁵Ca, sulfate and volume. Total ⁴⁵Ca excretion, urine calcium specific activity and urine phosphorus initially were depressed indicating an increase in the intestinal absorption of calcium, then were not significantly different from control values. After 10 months, analysis of the femur, tibia and mandible revealed no differences in wet weight, dry fat-free or ash weight, calcium, phosphorus, magnesium, or residual ⁴⁵Ca content. Specific gravity and ash density also were unaffected by protein intake, as were femur length and midshaft cortical thickness. No changes in bone composition were found which would indicate that high protein diets promote bone loss in this species. The adult rat appears to be capable of compensating for the increased urinary loss of Ca associated with an increment in acid load (whether derived from an increase in diet acidity or in metabolic acid production) by reducing the fractional loss of endogenous Ca in the feces.

KEY WORDS: • calciuria • dietary protein • bone metabolism

¹ Supported by the Ontario Ministry of Agriculture and Food and by the Natural Sciences and Engineering Research Council of Canada.

² Presented in part at the Third Joint Meeting of AIN, ASCN and NSC, Guelph, Ontario, 1979. Whiting, S. J. & Draper, H. H. (1979) Effect of diets high in protein, sulfur amino acids or sulfate on calcium metabolism in the adult rat. J. Nutr. 109, xxxiii (abs).

³ Present address: Department of Medicine, Nephrology Division, The University of British Columbia, Vancouver, B. C., V6T 1W5.

⁴ To whom reprint requests should be sent.

Manuscript received 22 May 1980.

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