Isoflavone intake is associated with various properties beneficial to human health which
are related to their antioxidant activity, for example, to their ability to increase LDL
oxidation resistance. However, the distribution of isoflavones among plasma lipoproteins
has not yet been elucidated in vivo. Therefore, the objective of the
present study was to investigate the association between daidzein (DAI) and lipoproteins
in human plasma upon administration of the aglycone and glucoside form. Five men aged
22–30 years participated in a randomised, double-blind study in cross-over
design. After ingestion of DAI and
daidzein-7-O-β-d-glucoside (DG) (1 mg DAI
aglycone equivalents/kg body weight) blood samples were drawn before isoflavone
administration as well as 1, 2, 3, 4·5, 6, 8, 10, 12, 24 and 48 h
post-dose. Concentrations of DAI in the different lipoprotein fractions (chylomicrons,
VLDL, LDL, HDL) and in the non-lipoprotein fraction were analysed using isotope dilution
capillary GC/MS. The lipoprotein fraction profiles were similar for all subjects and
resembled those obtained for plasma in our previously published study. The lipoprotein
distribution based on the area under the concentration–time profiles from
0 h to infinity in the different fractions were irrespective of the administered
form: non-lipoprotein fraction (53 %) > LDL (20 %) > HDL
(14 %) > VLDL (9·5 %) > chylomicrons
(2·5 %). Of DAI present in plasma, 47 % was associated to
lipoproteins. Concentrations in the different lipoprotein fractions as well as in the
non-lipoprotein fraction were always higher after the ingestion of DG than of DAI. Taken
together, these results demonstrate an association between isoflavones and plasma
lipoproteins in vivo.