Background: Soy consumption is known to reduce plasma total cholesterol and LDL cholesterol in hypercholesterolemic subjects, but the responsible soy components and the effects in normocholesterolemic subjects remain unclear.
Objective: The effects of soy isoflavone consumption on plasma total cholesterol, HDL-cholesterol, LDL-cholesterol, triacylglycerol, apolipoprotein A-I, apolipoprotein B, and lipoprotein(a) concentrations and on LDL peak particle diameter were examined in normocholesterolemic, premenopausal women.
Design: Thirteen healthy, normocholesterolemic, free-living, premenopausal female volunteers took part in this randomized, crossover-controlled trial. Each subject acted as her own control. Three soy isoflavone intakes (control: 10.0 +/- 1.1; low: 64.7 +/- 9.4; and high: 128.7 +/- 15.7 mg/d), provided as soy protein isolate, were consumed for 3 menstrual cycles each. Total cholesterol, HDL cholesterol, LDL cholesterol, and triacylglycerol were measured over the menstrual cycle. Apolipoprotein A-I, apolipoprotein B, lipoprotein(a), and LDL peak particle diameter were evaluated in the midluteal phase.
Results: Total cholesterol, HDL-cholesterol, and LDL-cholesterol concentrations changed significantly across menstrual cycle phases (P < 0.005). During specific phases of the cycle, the high-isoflavone diet lowered LDL cholesterol by 7.6-10.0% (P < 0.05), the ratio of total cholesterol to HDL cholesterol by 10.2% (P < 0.005), and the ratio of LDL to HDL cholesterol by 13.8% (P < 0.002).
Conclusions: Isoflavones significantly improved the lipid profile across the menstrual cycle in normocholesterolemic, premenopausal women. Although of small magnitude, these effects could contribute to a lower risk of developing coronary heart disease in healthy people who consume soy over many years.