Comparing the pharmacokinetics of daidzein and genistein with the use of 13C-labeled tracers in premenopausal women

Abstract

The serum pharmacokinetics of [(13)C]daidzein and [(13)C]genistein were reproducible among healthy women, and genistein was more bioavailable than was daidzein. Pharmacokinetics were unaffected by chronic exposure to soy foods. Urinary isoflavone concentrations correlated poorly with maximal serum concentrations, indicating the limitations of urine measurements as a predictor of systemic bioavailability. The bioavailability of both isoflavones was nonlinear at higher intakes, suggesting that uptake is rate-limiting and saturable.

Levels of urinary isoflavones and lignan polyphenols in Japanese women

“…Therefore, dietary intake of isoflavones was unlikely to differ between two groups. The half-life of daidzein is relatively shorter than that of equol, and the conversion of daidzein into equol is time-dependent and slow [21]. Therefore, daidzein could be excreted rapidly in urine before its conversion into equol.…”

The Soy Isoflavone Equol May Increase Cancer Malignancy via Up-regulation of Eukaryotic Protein Synthesis Initiation Factor eIF4G

“…Equol is a chiral molecule capable of existing in two enantiomeric forms: R-(ϩ) equol and S-(Ϫ) equol; the latter is the natural diasteromer produced by intestinal bacteria (6,11). Both equol enantiomers show better uptake and have higher bioavailability (65-83%) than the isoflavones daidzein (30 -40%) or genistein (7-15%) (57). Both enantiomers bind ERs, with R-equol showing a preference for ER␤ (13).…”

Estimating perchlorate exposure from food and tap water based on US biomonitoring and occurrence data

“…Urinary concentrations of daidzein and genistein did not correlate well with the ingested doses, possibly due to limited absorption of these isoflavones at higher doses (Setchell et al, 2003a). In contrast, plasma and urine lignan concentrations after flax seed consumption increased in a dose-dependent manner (Nesbitt et al, 1999).…”