Influences of dietary protein levels and phytate contents on zinc requirement in rats.

This study investigates whether the effects of increased dietary levels of soy protein on zinc-deficient rats are due to the dietary protein content. Rats were fed two levels of demineralized soy protein (DP) diets and two levels of egg albumin (EA) diets including 7 ppm zinc (Experiment 1). Growth was depressed in rats fed a 20% DP diet (0.43% phytate) but not in those fed a 10% EA diet containing 7 ppm zinc. Zinc concentrations in the serum, femur and kidney were lower in rats fed the 20% DP diet than those fed a 10% DP (0.20% phytate) diet, and they were also lower in rats fed the 10% EA diet than those fed a 5% EA diet. Zinc concentrations in the serum and femur of rats fed the 10% DP diet or the 20% DP diet were decreased compared with those fed the 5% EA diet or the 10% EA diet, respectively. Under zinc-deficient conditions (< 0.4 ppm Zn), the survival time shortened (Experiment 2) and the zinc concentration in the serum and femur decreased faster (Experiment 3) in rats fed the 10% EA diet compared with those fed the 5% EA diet. The survival times and time courses of these parameters show that the zinc requirements of rats increased with the dietary protein level. The increased zinc requirement of rats that accompanied increasing dietary soy protein was due to the dietary protein content as well as the dietary phytate content.