Possible Adverse Effects of Soy Isoflavone Mixture on Pregnant and Lactating Rats and their Suckling Pups

Abstract

There is general agreement that soy isoflavones can be beneficial to health in adults. However, isoflavones are well known as endocrine-disrupting chemicals. The possibility that soy foods might adversely affect the reproductive system of mothers and infants should be considered. The aim of this study was to evaluate the adverse effects of a soy isoflavone mixture on rat dams and their offspring. The rat dams were fed diets containing the isoflavone mixture (commercial name: Soyact, aglycone type) at 0, 0.25, 0.5 and 1.0 g/kg as total isoflavones from pregnancy day 5 to postnatal day 13. We found that the dietary soy isoflavone mixture decreased the dam body weights in a dose-dependent manner and that the number of pups also tended to decrease. Genistein and daidzein were detected in the blood of the dams and the stomach contents of the suckling pups. The concentrations of daidzein were higher than those of genistein. We also found the transfer of isoflavones to the fetus. The reproductive output and fetus numbers were not significantly different in the isoflavone groups compared with the control group. The number of absorbed fetuses tended to increase though not significant. Our experiments suggested that soy isoflavones have the possibility of inducing adverse effects on endocrinic functions and others in animal studies at very high doses.