Assessment of urinary isoflavones among premenopausal women

Abstract

Epidemiological and clinical studies researching the effects of soy food intake require a high compliance to a soy diet protocol. Measuring isoflavones in the bodily fluids is the most objective method in determining dietary compliance because isoflavones are highly and positively correlated with soy food intake and specific to soy foods. Urine analysis is preferred over plasma due to its noninvasiveness, which aids in compliance. Our study investigated the accuracy of collecting weekly and single day samples from 19 premenopausal women on a daily soy diet protocol in comparison to monthly samples for determining dietary compliance. We compared urinary isoflavone excretion rates (UIER) of weekly samples and single day samples to the UIER of a monthly sample that consisted of urine collected daily. Correlations were high between all samples and the monthly UIER. The correlations of the mean of all weeks UIER and single day UIER with the monthly UIER were 0.96 and 0.89, respectively. No large differences were seen when samples were stratified by ethnicity, 8MI, and equol excretor status. The small degree of increased accuracy in determining dietary compliance in measuring monthly UIER compared to weekly does not justify the extra time and effort required by the subjects and staff. Therefore, we conclude that analyzing weekly UIER is an accurate and feasible method of determining dietary compliance with a soy-based diet