Volume 89, Issue 4, April (2003), pp. 467-475 © The Author 2003
doi:10.1079/BJN2002807

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Effects of supplementation with purified red clover (Trifolium pratense) isoflavones on plasma lipids and insulin resistance in healthy premenopausal women

Sarah J. Blakesmith¹, Philippa M. Lyons–Wall¹, Caroline George¹, George E. Joannou¹, Peter Petocz² and Samir Samman^1,*
1Human Nutrition Unit, School of Molecular and Microbial Biosciences, University of Sydney, Australia
²School of Mathematical Sciences, University of Technology, Australia

 (Received 3 January 2002 –Revised 31 October 2002–Accepted 5 November 2002)

Consumption of isoflavone-rich soyabean protein is reported to reduce total and LDL-cholesterol, but the specific components responsible are undetermined. In a previous crossover trial we showed that purified isoflavones, derived from red clover (Trifolium pratense), raised HDL₃-cholesterol in premenopausal women; however, these findings were inconclusive due to period and carryover effects. In an attempt to overcome this problem, we utilised a parallel study designed to re-examine the effects of purified isoflavones on plasma lipoproteins and markers of insulin resistance in premenopausal women. Twenty-five healthy premenopausal women participated in a double-blind, randomised, parallel study. The treatment group (n 12) consumed a placebo for the first menstrual cycle and an isoflavone supplement (86 mg/d, derived from red clover) for three cycles, while the placebo group (n 13) consumed a placebo supplement for four menstrual cycles. Blood samples were collected weekly during cycles 1, 3 and 4. Supplementation with isoflavones resulted in a 15-fold increase in urinary isoflavone excretion (P<0·0001). There were no significant effects on total cholesterol, LDL- and HDL-cholesterol, HDL subfractions, triacylglycerol, lipoprotein(a), glucose or insulin concentrations. Our present results indicate that purified isoflavones derived from red clover have no effect on cholesterol homeostasis or insulin resistance in premenopausal women, a group which is at low risk of CHD.

Abbreviations: Lp(a); lipoprotein(a)
Corresponding Author: Associate Professor Samir Samman, fax +61 2 93516022, email s.samman@mmb.usyd.edu.au

Keywords:
Isoflavones: Lipids: Premenopausal women