Phytoestrogens and cardiovascular disease

Abstract

The most extensively studied class of phytoestrogens, isoflavones, occur in soybeans and other legumes. Six systematic reviews have assessed the effects of soy isoflavones on lipid levels, and suggested that a diet supplemented with soy protein isolate (ISP) containing isoflavones reduces low-density lipoprotein (LDL) cholesterol by around 0.15 mmol/L, but without clear effects on triglycerides or high-density lipoprotein (HDL) cholesterol. However, no review has suggested that purified soy isoflavones or soy protein without isoflavones (where the isoflavones have been removed by an alcohol wash) have statistically significant effects. It remains unclear which are the active components of soy. They may include soy protein which has not been denatured by alcohol wash, interaction of isoflavones within the intact soy matrix, or other compounds removed in the alcohol-extracted fraction. The reduction in total cholesterol may be greater in men than in postmenopausal women. There is little evidence that the effectiveness of soy varies with baseline serum lipid levels, or the amount of isoflavone or soy protein consumed. However, changes in triglycerides may be related to baseline levels. While there is no evidence of beneficial effects of phytoestrogens on blood pressure, arterial compliance or oxidation of LDL cholesterol, there may be beneficial effects on endothelial function in postmenopausal women, and on homocysteine concentrations. There is little suggestion of adverse effects of soy or isoflavones at physiological doses, although those taking soy isoflavone supplements do appear to have higher levels of gastro intestinal and menstrual complaints. There have been no published trials on the effects of phytoestrogens on mortality or cardiovascular events, so studies currently rely on the above bio markers of risk. Most evidence relates to soy isoflavones, but there is some evidence for lignans. Further robust studies assessing the effects of whole soy foods on cardiovascular outcomes are needed.