Effects of Isoflavone Dietary Supplementation on Cardiovascular Risk Factors in Type 2 Diabetes

Abstract

A diet supplemented with soy protein and isoflavones has been shown to reduce cardiovascular risk factors in postmenopausal women with type 2 diabetes. However, it remains unclear which component is responsible for these effects. Our aim was to determine whether the addition of isoflavones alone modifies cardiovascular disease risk markers in this group of patients. Cardiovascular disease (CVD) is the leading cause of mortality in women in developed countries (1), and women with diabetes are four times more likely to die from CVD than men (2). Among other factors, postmenopausal estrogen depletion, greater insulin resistance, and dyslipidemia (3,4) may contribute to high risk of accelerated CVD.Modification of lifestyle is important to reduce CVD risk factors and delay progression of type 2 diabetes-associated complications. In particular, the addition of oral supplements, such as soy products, as part of a healthy diet has attracted recent interest because of their beneficial effects on lipid profiles (5-10). However, scant information is available on the effects of soy in individuals with type 2 diabetes (11-13), who are at higher risk due to hyperlipidemia, lower HDL levels, and abnormalities in LDL/lipoprotein composition (14). It also remains unclear whether a beneficial effect can be attributed to the soy protein or isoflavones.We have shown that soy protein combined with isoflavones can improve glycemic control, insulin resistance, and lipids in patients with type 2 diabetes (11). Therefore, our aim was to determine if this effect was due to the isoflavone component alone. RESEARCH DESIGN ANDMETHODS -This was a randomized, double-blind, placebo-controlled, crossover study with a 4-week washout period separating the placebo and active phases (12 weeks each). Subjects provided informed consent. Randomization was performed using a random number generator. Thirty-two Caucasian, postmenopausal women with diet-controlled type 2 diabetes (according to World Health Organization criteria) (15) and amenorrhoa (for Ͼ1 year) were recruited. Exclusion criteria were breast/uterine cancer; uncontrolled hypothyroidism; and treatment with oral hypoglycemic agents, insulin, estrogens, or statins initiated Ͻ4 months before the trial.Baseline characteristics are included in Table 1. Six subjects withdrew from the study: one required a cholecystectomy and one a coronary angioplasty, one had an acute attack of polymyalgia rheumatica requiring steroids, and three were unable to comply with study requirements. InterventionThe soy preparation (Essential Nutrition) contained 132 mg isoflavones (53% genistein, 37% daidzein, and 10% glycitein). It was devoid of soluble fiber. The placebo was an identical tablet of microcrystalline cellulose. Compliance was monitored by counting returned medication. Study measurementsVenous blood samples were collected at each visit after a 12-h overnight fast. A1C, glucose, and lipid levels were measured using standard methods. LDL cholesterol was calculated using the Friedewald equation and insulin...

Soy Reduces Bone Turnover Markers in Women During Early Menopause: A Randomized Controlled Trial

“…(25) A recent meta-analysis suggested that soy isoflavones significantly reduced total cholesterol and LDL-C but do not change HDL-C. (27) These differences may be attributed to the basal lipid profile or different study designs and isoflavones composition with glucoside instead of aglycone forms. There was a significant reduction in systolic blood pressure within 6 months of SPI supplementation but no change with SP supplementation.…”

“…(32) These data suggests that a synergistic matrix of soy protein and isoflavones is needed to maximize the effects rather than either soy protein or isoflavone alone. (25,33) In the current study, where all patients had normal thyroid function tests at baseline, none of the patients developed subclinical or overt hypothyroidism. There was also no significant change in fT3 with either SPI or SP supplementation.…”

“…(24) In addition, soy has been shown to inhibit insulin secretion from pancreatic b cells. (25) This study is the first to use a control soy preparation that was truly isoflavone-free and as it showed no treatment effects it suggests soy protein alone is inert in relation to bone health. There were no changes in body weight after 24 weeks of soy, suggesting that the reduction in insulin resistance was independent of the action of soy fiber that might enhance satiation and hence induce weight loss.…”

Raloxifene, soy phytoestrogens and endothelial function in postmenopausal women

“…Whereas some investigators have reported neutral effects of soy on serum lipids 36,37 , beneficial effects have been reported by others 35,[38][39][40] . Recently, favorable effects of soy supplementation on metabolic control in diabetes were reported by Jaygopal and colleagues 41,42 . Thus, despite the neutral effects of soy observed in this study, the possibility of cardioprotective effects, at least in certain population subgroups, still exists.…”

Scientific Opinion on the substantiation of health claims related to soy isoflavones and protection of DNA, proteins and lipids from oxidative damage (ID 1286, 4245), maintenance of normal blood LDL cholesterol concentrations (ID 1135, 1704a, 3093a), reduction of vasomotor symptoms associated with menopause (ID 1654, 1704b, 2140, 3093b, 3154, 3590), maintenance of normal skin tonicity (ID 1704a), contribution to normal hair growth (ID 1704a, 4254), “cardiovascular health” (ID 3587), treatment of prostate c

“…A meta-analysis of randomised controlled trials (RCTs) (Taku et al, 2008), which assessed the effects of consumption of extracted soy isoflavones vs. placebo on blood LDL-cholesterol concentrations, included the individual studies of this type which were provided in the consolidated list (Cheng et al, 2007;Gonzalez et al, 2007) except three Lissin et al, 2004;Nahas et al, 2007).…”