Effect of dietary phytate/zinc molar ratio on growth and bone zinc response of rats fed semipurified diets.

In rats fed semipurified diets, bioavailability of dietary zinc was tested at different phytate/zinc molar ratios; growth and zinc in femurs were the criteria of adequacy. On diets with 10--12 ppm zinc, the growth of rats was not affected by phytate/zinc molar ratios of 12 or less if the level of dietary calcium was 0.75% but was depressed at ratios greater than 6 if the level of calcium was 1.75%. Phytate/zinc molar ratios greater than these did not depress growth if the dietary zinc concentration was at least 2.5 and 5 times the minimal requirement for growth at dietary calcium levels of 0.75 and 1.75%, respectively. At the maximum phytate/zinc molar ratio that did not depress growth, accumulation of zinc in femurs was depressed. Small increases in dietary calcium (from 0.75 to 0.87%) depressed growth of rats fed diets with 12 ppm zinc and a phytate/zinc molar ratio of 25. Preformed Zn3 and Zn6 phytate preparations were equivalent to ZnSO4.7H2O as dietary zinc sources. The data indicated that high dietary calcium per se reduced zinc bioavailability. The maximum phytate/zinc molar ratio that did not depress growth of young rats was greatly influenced by dietary calcium level and somewhat influenced by total dietary zinc concentration.