Soy isoflavone variability in postmenopausal women

Abstract

The purpose of this Master’s thesis was to examine the variability related to isoflavone metabolism in postmenopausal women. The study involved 124 postmenopausal women who consumed 80 or 120 mg of isoflavones per day during a three year time period. The isoflavones genistein, glycitein, daidzein, dihydrodaidzein (DHD), O-desmethylangolensin (ODMA), and equol were extracted and characterized from 24 h urinary samples. Overall, there was little effect of time on the excretion of isoflavones. There was a significant effect of treatment on the excretion of genistein, glycitein, and ODMA where daily excretion was higher for the 120 mg/d group compared to the 80 mg/d group. Intra-individual variability was high, with percent coefficients of variation (%CVs) ranging from 32-64%. Inter-individual variability was found to be higher than intra-individual variability, with %CVs ranging from 40-256%. Approximately 36% of the subjects were defined as equol producers. In addition, approximately 16% of the women experienced a change in equol-producing status which was found to be significantly related to reported antibiotic use. Finally, equol was the only metabolite for which excretion significantly decreased with reported antibiotic use. In conclusion, isoflavone excretion was found to be highly variable both within and between women. Results from this study also indicate that antibiotic use has a profound effect on the ability to produce equol.