The effects of soy-derived phytoestrogens on serum lipids and lipoproteins in moderately hypercholesterolemic postmenopausal women. The effect of soy protein with or without isoflavones relative to milk protein on plasma lipids in hypercholesterolemic postmenopausal women. The effects of soy protein in women and men with elevated plasma lipids. Isoflavones and clinical cardiovascular risk factors in obese postmenopausal women: a randomized double-blind placebo-controlled trial.
Postmenopausal women are at an increased risk of developing coronary artery disease (CAD). This increase is due primarily to elevated cholesterol concentrations accompanying the loss of endogenous estrogen secretion. Recently, the consumption of soy foods has been shown to reduce serum cholesterol concentrations. Phytoestrogens (PE) have been proposed as the responsible agents of the hypocholesterolemic effect of soy foods. However, few studies have investigated the effect of PE supplementation on serum lipoproteins. The purpose of the present study is to investigate the effects of PE supplementation (150 mg) on serum lipids and lipoproteins in moderately hypercholesterolemic, elderly, postmenopausal women. Thirty-six subjects were randomized into two groups and received either a 150-mg PE supplement/d (n = 20) or a placebo (n = 16). Serum samples obtained at baseline and 2 months were analyzed for total triacylglycerol, total cholesterol, and high density lipoprotein cholesterol using standard Lipid Research Clinic procedures. In addition, total triacylglycerol and cholesterol were measured after 6 months of treatment. The t test and ANOVA were employed to compare the two groups. The results (mean +/- SEM) indicated no significant differences in total triacylglycerol (1.3 +/- 0.2 vs. 1.2 +/- 0.2 mmol/liter), total cholesterol (6.4 +/- 0.4 vs. 6.5 +/- 0.2 mmol/liter), or high density lipoprotein cholesterol (1.0 +/- 0.1 vs. 1.0 +/- 0.1 mmol/liter) between the placebo and the PE groups, respectively, after 2 months of treatment. Moreover, total triacylglycerol and cholesterol remained unchanged after 6 months. Our findings suggest that PE supplementation with 150 mg/d over a 6-month period does not significantly alter serum lipoproteins in postmenopausal women and, therefore, may not effectively reduce the risk of CAD in this population. Clinical trial data and the results of a meta-analysis suggest a hypocholesterolemic effect of soy protein. The effect may be partially attributable to the isoflavones in soy. Few studies have examined the separate effects of soy protein and isoflavones.
                The objective of this study was to determine the effect of soy protein and isoflavones on plasma lipid concentrations in postmenopausal, moderately hypercholesterolemic women.
                This was a randomized, double-blind, placebo-controlled clinical trial with 3 treatment groups. After a 4-wk run-in phase during which the women consumed a milk protein supplement, the subjects were randomly assigned to 12 wk of dietary protein supplementation (42 g/d) with either a milk protein (Milk group) or 1 of 2 soy proteins containing either trace amounts of isoflavones (Soy- group) or 80 mg aglycone isoflavones (Soy+ group).
                LDL-cholesterol concentrations decreased more in the Soy+ group (n = 31) than in the Soy- group (n = 33) (0.38 compared with 0.09 mmol/L; P = 0.005), but neither of these changes was significantly different from the 0.26-mmol/L decrease observed in the Milk group (n = 30). The results for total cholesterol were similar to those for LDL cholesterol. There were no significant differences in HDL-cholesterol or triacylglycerol concentrations between the 3 groups.
                The difference in total- and LDL-cholesterol lowering between the 2 soy-protein supplements suggests an effect attributable to the isoflavone-containing fraction. However, the unexpected LDL-cholesterol lowering observed in the Milk group, and the fact that there was no significant difference between either soy group and the Milk group, suggests that changes may have been due to other factors related to participation in the study. Fifty four postmenopausal women with elevated cholesterol were recruited for a randomised, double-blind controlled trial of soy protein containing isoflavones. (ISP+) or a soy protein with a low isoflavone content (ISP-), taken daily for 12 weeks. There was an overall reduction after 12 weeks in total cholesterol (TC), LDL cholesterol (LDL-C), sex hormone binding globulin (SHBG), and luteinizing hormone (LH). There were no significant differences between treatment groups. In a separate study 27 male subjects with a TC > 5.5 mmol/l were given ISP+ for 12 weeks. In this male study there was a significant increase in HDL cholesterol (HDL-C) and SHBG. Soy protein has a cholesterol lowering effect in both women and men. These studies suggest that this effect is independent of isoflavones. Soy protein also reduces SHBG levels in both sexes. To investigate whether 6 months of isoflavone supplementation, which has been shown to be sufficient to improve menopausal symptoms, could also improve clinical cardiovascular disease (CVD) risk factors in obese postmenopausal women, compared with a placebo.
                A randomized double-blind placebo-controlled trial in which 50 obese postmenopausal women were divided into two groups (isoflavones vs. placebo) to examine the effect of 6 months of isoflavone supplement (70 mg) on clinical CVD risk factors. Body composition (DXA), medical and social characteristics, daily energy expenditure (accelerometry), dietary intake (3-day dietary record), and blood biochemical analyses (lipid profile, insulin, glucose) were obtained.
                At baseline, no differences were found between groups except for fasting insulin level. Women were thus considered at risk of CVD based on body composition but not biochemical variables. After 6 months, we observed that isoflavones did not favorably affect risk factors predisposing to CVD (biochemical or body composition) compared with placebo.
                Isoflavones given for 6 months should not be considered protective against clinical CVD risk factors in obese postmenopausal women. Nevertheless, further research is needed to verify if isoflavones protect against CVD disease risk factors when administered for a longer duration or when combined with nutritional or exercise interventions. It would also be pertinent to study their effects in women with specific metabolic abnormalities.
We found no evidence for effects of isoflavones on patient-important outcomes or lowering of cholesterol levels in people with hypercholesterolaemia. Our findings have to be interpreted with caution due to high or unclear risk of bias in several risk of bias domains, and low number of participants in trials.