A BENEO-Orafti Newsletter - Spring 2008 - Nr. 18:
Prebiotics and healthy ageing
Monitor
Inulin enhances blood isoflavones levels after soy intake in post-menopausal women
In post-menopausal women, soybean isoflavones are increasingly popular as alternative to conventional hormone replacement therapy because of their potential health benefits (effects on bone, hot flushes, etc). Bacterial glucosidases (e.g. from lactobacilli, bacteroides and bifidobacteria) metabolise isoflavones in the intestinal tract and thereby affect their absorption.
The aim of the study was to assess the effect of inulin on plasma isoflavone levels after intake of soybean isoflavones in post-menopausal women. Twelve healthy post-menopausal women (51-64 years of age) participated in this randomised, double-blind, cross-over study and consumed 40 mg of a conjugated form of soybean isoflavones with or without 3.66 g of inulin twice daily in two 21-day intervention periods (7-day washout period in between).
After 21 days of supplementation with the soy isoflavones, the area under the curve (AUC0-24) values for daidzein and genistein (blood levels) were higher than those at baseline (day 1) with both formulations (soy alone and soy plus inulin, P<0.05 vs. baseline for both). However, AUC0-24 values on day 21 for both isoflavones were significantly higher after the isoflavone plus inulin formulation than after the isoflavone alone. The increase was 38% for daidzein (P<0.01) and 91% for genistein (P<0.01). The maximum postprandial concentration in plasma (Cmax) of daidzein appeared to be higher after 21 days of supplementation with both formulations (P<0.05 vs. baseline for both). In contrast, plasma Cmax values of genistein appeared to be higher only after supplementation with the isoflavone plus inulin formulation (P<0.05 vs. baseline). The time for Cmax to be reached (tmax) was decreased for both genistein and daidzein after 21 days of both supplementations (P<0.05 vs. baseline for both), but was not different between both formulas. The pharmacokinetic parameters of daidzein and genistein are given in Figures 1 and 2, respectively.
To conclude, the results of this study show that supplementation with inulin increased plasma concentrations of soybean isoflavones most probably via its effect on the microflora (e.g. stimulation of bifidobacteria) thereby facilitating glucoside conversion and hence isoflavone absorption.
Piazza C, Giovanna M, Melilli B, Incognito T, Marano MR, Leggio GM, Roxas MA, Drago F (2007) Influence of inulin on plasma isoflavone concentrations in healthy postmenopausal women. Am. J. Clin. Nutr. 86: 775-780.
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