Effects of subacute magnesium deficiency and soy protein isolate on growth and reproduction in rats

Abstract

To investigate the interaction of magnesium depletion and source of protein, female weanling Sprague-Dawley rats were fed diets based on casein or soy protein isolate which contained either adequate or suboptimal levels of magnesium (approximately 200 ppm). Animals were sacrificed after 42 and 100 days and after gestation. Magnesium deficiency was reflected in reduced carcass, bone and plasma magnesium but not in hepatic concentration. Zinc concentration was decreased in bone in those animals which were magnesium deficient and was further reduced in those fed the soy protein diet which was low in magnesium. Altered zinc status was also presumptively demonstrated by the reduced plasma alkaline phosphatase levels in rapidly growing rats fed soy protein regardless of magnesium content. The enzyme level was depressed in the group fed the casein magnesium deficient diet but not to the extent of that for the soy diet groups. However, the growth retardation which developed in the casein magnesium-deficient rats may have resulted in a longer period of rapid growth accounting for the higher specific activity of plasma alkaline phosphatase. Hemoglobin levels were adversely affected by magnesium deficiency but not by soy protein, while hematocrit was not consistently altered. Magnesium deficiency resulted in decreased fertility, reduced ability of the dam to bring a litter to term, intrauterine growth retardation, more difficult and prolonged delivery and markedly reduced viability of pups. Cyanosis prevalent in litters from magnesium-deficient animals was indicative of fetal anemia. Magnesium and nitrogen content of litters was lowest in the casein low-magnesium group although fetal zinc content was lowest in the litters from the mothers fed the soy protein isolate diet with low suboptimal intakes of magnesium concentration. These results lend support to the concern over suboptimal intakes of magnesium and of zinc by women in the reproductive age groups especially when combined with increased utilization of soy protein in the diet.