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Dietary Protein, as Egg Albumen: Effects on Bone Composition, Zinc Bioavailability and Zinc Requirements of Rats, Assessed by a Modified Broken-Line Model¹

U.S. Department of Agriculture, Agricultural Research Service, Grand Forks Human Nutrition Research Center, Grand Forks, ND

The effect of dietary protein concentration on zinc bioavailability, requirements and incorporation into bones was investigated in growing rats. Zinc requirements were determined by the broken-line method. Protein did not affect either absorption or biological half-life of ⁶⁵Zn added to the diet. Zinc requirements based on weight gain or tibia zinc were generally greater when rats were fed 30% rather than 15% egg white. When fed 30% rather than 15% egg white, zinc-deficient rats gained less weight and tended to incorporate less zinc into bone, whereas zinc-adequate rats gained weight similarly and incorporated more zinc into bone. Dietary protein concentration apparently elevated the maximum amount of zinc incorporated into bones of rats fed adequate zinc. When dietary zinc was adequate (25 mg/kg diet), tibia zinc concentrations increased linearly with dietary concentrations of 15, 25, 35 and 45% egg white. When dietary zinc was adequate, higher protein diets resulted in lower tibia nitrogen, and higher tibia zinc, without substantial changes in tibia size or calcium concentration. These results indicate that high protein diets increase zinc requirements and bone zinc deposition, the latter being a consequence of altered bone zinc metabolism, rather than improved zinc bioavailability.

KEY WORDS: • zinc bioavailability • bone zinc deposition • dietary protein • nutrient requirements • rats • modified broken-line model

¹ Presented in part at meetings of the Federation of American Societies for Experimental Biology, March 19–24, 1989, New Orleans, LA [Hunt, J. R. & Johnson, L. K. (1989) Effect of protein intake on tibia Zn and Zn requirements. FASEB J. 3: A652] and the North Dakota Academy of Sciences, April 27–28, 1989, Grand Forks, ND [Hunt, J. R. & Johnson, L. K. (1989) The effect of dietary protein intake on zinc requirements and bone zinc in the growing rat. Proc. N.D. Acad. Sci. 43: 54] and April 19–20, 1990, Fargo, ND [Tekle-Wolde, C. A. & Hunt, J. R. (1990) The effects of dietary protein intake on bone composition in the growing rat. Proc. N.D. Acad. Sci. 44: 89].

Manuscript received 7 August 1990. Revision accepted 3 July 1991.

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