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Dietary factors are considered important environmental risk determinants for western diseases. Studies have revealed beneficial or protective effects of the consumption of legumes with regard to hypercholesterolaemia and coronary heart disease, obesity, diabetes mellitus, and menopause. During the last decade attention has been focused on soy and soybean products. Several constituents have been isolated: isoflavones, phytosterols, pretense inhibitors, inositol hexaphosphate, and saponins. Our interest concentrates on hormone-like bisphenolic phytoestrogens of dietary origin, the lignans and isoflavonoids. Their glycosides, converted by gut bacteria to mammalian derivatives with weak estrogenic and antioxidative activity, originate in leguminous seeds. we developed an isotope dilution gas chromatography-mass spectrometry method for quantitative determination of the isoflavones, formononetin, biochanin A, daidzein, genistein and coumestrol, and the lignans secoisolariciresinol and matairesinol, in food samples. We measured the four isoflavonoids and coumestrol, and for the first time, the two lignans in 52 leguminous seeds and found high concentrations of isoflavonoids (0-1853.35 mg/kg, 0-7.3 mmol/kg dw) but lower amount of lignans (0-15.85 mg/kg; 0.05 mmol/kg dw). The highest plasma levels of their metabolites are found in individuals living in countries or regions with low cancer and cardiovascular disease incidence and these are probably sufficient to influence intracellular enzymes, protein synthesis, growth factor action, malignant cell proliferation, differentiation, arid angiogenesis. Leguminous seeds, therefore, in respect to their abundant concentrations of phytoestrogens, are strong candidates for a role as natural cancer-protective food. (C) Elsevier Science Inc. 1998.