Urinary isoflavonoid excretion in humans is dose dependent at low to moderate levels of soy-protein consumption

Abstract

Soybeans contain isoflavones, which have been associated with many health benefits, including decreased cancer risk. The purpose of our study was to measure urinary isoflavonoid excretion in response to daily consumption of soy that contained 0-36 mg isoflavones--a lower range than used in previous studies--and to compare urinary isoflavonoid excretion between equol excreters and nonexcreters. Fourteen men and women aged 20-40 y participated in the study. Half of the subjects were identified previously as equol excreters and the other half as equol nonexcreters. This randomized, double-blind, crossover study consisted of four 9-d diet treatment periods. During each treatment period participants consumed a low-photoestrogen controlled diet and a beverage containing 0, 5, 10, or 20 g soy protein. Urine collected on the last 3 d of each treatment period was analyzed for isoflavonoid (equol, O-desmethylangolensin, genistein, and daidzein) and lignan (enterodiol and enterolactone) contents by using isotope-dilution gas chromatography-mass spectrometry. There was a highly linear dose response of urinary isoflavonoid excretion to soy consumption, which did not differ significantly between equol excreters and nonexcreters. There were no significant differences in lignan excretion between the two diet treatments. Our results indicate that urinary isoflavonoid excretion is dose dependent in humans at low to moderate levels of soy consumption.

Urinary isoflavonoid excretion is inversely associated with the ratio of protein to dietary fibre intake in young women

“…Some previous studies have reported a reciprocal relationship between excretion of equol and O-dma (Hutchins et al, 1995;Kelly et al, 1995;Arai et al, 2000) although this was not confirmed in the current study or other studies (Karr et al, 1997;Lampe et al, 1998;Rowland et al, 2000). Interest is focused on equol since this metabolite has greater oestrogenic potency than either daidzein or O-dma and therefore excretor status could have physiological implications.…”

“…A dose-dependent relationship has been reported between intake and mean excretion of isoflavonoids after 9-day treatments with four levels of soy protein (Karr et al, 1997). However, intervention studies with soy products have reported surprisingly wide, largely unexplained variation in the excretion of isoflavonoids between individuals ingesting the same dose (Kelly et al, 1993;Hutchins et al, 1995;Tew et al, 1996;Lampe et al, 1998;Slavin et al, 1998;Rowland et al, 2000).…”

Urinary isoflavone excretion as a compliance measure in a soy intervention among young girls: a pilot study

“…These conflicting results raise questions about the accuracy of the self-reported data and support the importance of having multiple compliance measures. Given the association between dietary soy intake and urinary isoflavone excretion observed in previous soy intervention studies in adults (Karr et al, 1997;Maskarinec et al, 2003), urinary isoflavone excretion likely provides a more objective measure than self-reported dietary data in children. On the other hand, the decline in urinary isoflavone excretion levels could also result from a longer time period between urine collection and soy food consumption.…”

Urinary phytoestrogen concentrations in the U.S. population (1999–2000)

“…About 30-50% of individuals consuming an isoflavone-rich diet excreted daidzein but little or no equol suggesting a significant interindividual variation in daidzein metabolism (Setchell et al, 1984;Kelly et al, 1995;Karr et al, 1997;Lampe et al, 1998;Rowland et al, 2000). Sex, antibiotic use, and basal diet composition have been identified as factors influencing phytoestrogen metabolism.…”