Soy isoflavone conjugation differs in fed and food-deprived rats

An experiment clarifying the influence of food deprivation on the isoflavon e conjugation pattern in rats was conducted. Food-deprived and fed rats wer e administered daidzein and genistein at 7.9 mu mol/kg body, and changes in their plasma metabolites (i.e., free compounds, sulfates, glucuronides, su lfates/glucuronides) were measured quantitatively as a function of time. In the food-deprived group, total plasma daidzein and genistein reached maxim um concentrations of 20.9 +/- 4.4 and 11.4 +/- 3.1 mu mol/L, respectively, 10 min after administration, whereas in the fed group, the maxima were 2.4 +/- 0.8 mu mol/L for daidzein after 2 h and 1.8 +/- 0.2 mu mol/L for genist ein after 4 h. In both groups, there were significantly more daidzein sulfa tes than genistein sulfates. Moreover, depriving rats of food before daidze in and genistein administration significantly increased plasma isoflavone s ulfates with simultaneous significant decreases in plasma isoflavone glucur onides compared with fed rats. Additionally, nonconjugated daidzein and gen istein appeared in plasma of food-deprived rats for 1 h after administratio n. Plasma concentrations of conjugates having both sulfate and glucuronide moieties were not significantly different between the groups.