The effect of supplementation with isoflavones on plasma lipids and oxidisability of low density lipoprotein in premenopausal women

Results of recent clinical studies have lead to the hypothesis that isoflavones are cardioprotective. The aims of this trial were to determine the effect of supplementation with isoflavonoid phytoestrogens on plasma cholesterol concentrations and its distribution among lipoproteins and whether supplementation with isoflavones influences oxidisability of low density lipoprotein (LDL) ex vivo. Fourteen healthy premenopausal women participated in a randomised cross-over trial lasting four menstrual cycles (approximately 4 months). The subjects were asked to consume 86 mg of isoflavones daily for the duration of two menstrual cycles followed by placebo for an equivalent period, or vice versa. Venous blood samples were collected initially and at the end of the second and fourth menstrual cycles for the determination of plasma lipid concentrations and the resistance of LDL to copper-induced oxidation ex vivo. Accustomed dietary intake of isoflavones and lignans during the placebo period were 6.87±3.0 and 1.80±0.22 mg/day (mean±S.E.M.), respectively, and these did not change during the supplementation period. The intake of other dietary components remained constant during the trial. Supplementation resulted in a 5-fold increase in urinary isoflavone excretion (12.2±14.2 versus 70.1±10.3 μmol/24 h, placebo and isoflavone periods, respectively, P=0.0001). No changes in the oxidisability of LDL (lag time of 32.9±3.1 versus 30.4±2.9 min) or the plasma concentrations of total cholesterol (4.03±0.21 versus 4.11±0.18 mmol/l) or triacylglycerol (0.67±0.04 versus 0.73±0.06 mmol/l) were observed following supplementation. However a significant period effect (P=0.024) was observed and a trend towards a carryover effect (P=0.086) was noted for the concentration of HDL3 cholesterol. Further studies are required to clarify the potential effect of isoflavones on HDL metabolism and the interaction with plasma steroid hormones during the menstrual cycle.