Alterations in Clinically Important Phytoestrogens in Genetically Modified, Herbicide-Tolerant Soybeans

Abstract

The growing clinical interest in and use of soybean-based food products or extracts to increase dietary phytoestrogen intake makes the precise composition of the key biologically active ingredients of soybeans, notably genistin and daidzin, of substantial medical interest. Conventional soybeans are increasingly being replaced by genetically modified varieties. We analyzed the phytoestrogen concentrations in two varieties of genetically modified, herbicide-tolerant soybeans and their isogenic conventional counterparts grown under similar conditions. An overall reduction in phytoestrogen levels of 12-14% was observed in the genetically altered soybean strains, mostly attributable to reductions in the concentrations of genistin and, to a lesser extent, in daidzin. Significant sample-to-sample variability in these two phytoestrogens, but not in glycitin, was evident in the genetically altered soybeans. Given the high biological potency of isoflavones and their metabolic conversion products, these data suggest that genetically modified soybeans may be less potent sources of clinically relevant phytoestrogens than their conventional precursors. These observations, if confirmed in other soybean varieties, heighten the importance of establishing baselines of expected isoflavone levels in transgenic and conventional soy products to ensure uniformity of clinical results. Disclosure of the origins and isoflavone composition of soyfood products would be a valuable adjunct to clinical decision-making.