Soy protein reduces the arterial low-density lipoprotein (LDL) concentration and delivery of LDL cholesterol to the arteries of diabetic and nondiabetic male cynomolgus monkeys

Soy and the risk of type 2 diabetes mellitus: A systematic review and meta-analysis of observational studies

BACKGROUND

Increasing studies have focused on the relationship between soy intake and type 2 diabetes mellitus risk, but the results are inconsistent. We conduct a meta-analysis to evaluate the relationship.

METHODS

The databases of PubMed, Web of Science and Embase were searched up to Dec 2016. A random-effect model was used to pool the results of included studies.

RESULTS

Eight studies with 19 reports met the inclusion criteria. A significant inverse association was shown between soy intake and type 2 diabetes mellitus risk with an overall RR of 0.77 (95% CI = 0.66-0.91) with high heterogeneity. Besides, there was an obvious relationship between soy protein and isoflavones intake and risk of T2DM with the summary RR was 0.88 (95% CI = 0.80-0.97) with no heterogeneity. In the subgroup analysis, a statistically significant protective effect of soy consumption was observed in women (RR = 0.65; 95% CI = 0.49-0.87), cross-sectional studies (RR = 0.45; 95% CI = 0.30-0.67), and Asian populations (RR = 0.73; 95% CI = 0.61-0.88).

CONCLUSIONS

Soy products and soy constituents (soy protein and soy isoflavones) may be associated with a lower risk of type 2 diabetes mellitus. Future studies should focus on the dose-response effect and the mechanism.

A BRIEF COMMUNICATION

Nutritional supplements containing soybean phytoestrogens, the isoflavones genistein (G) and daidzein (D), are increasingly used as alternative therapy for osteoporosis, cancer, and cardiovascular and other diseases with a frequency that increases with advancing age. In this study we examined the effects of subcutaneous administration of either G or D on serum lipid levels in orchidectomized (Orx) and intact (IA) middle-aged male rats, which are experimental models of andropause. Sixteen-month-old Wistar rats were treated with 10 mg/kg and 30mg/kg of either G or D. The control groups received testosterone, estradiol, or vehicle for 3 weeks, after which the total serum cholesterol (TC), low-density lipoprotein (LDL-C), high-density lipoprotein (HDL-C), and total triglycerides (TT) were measured. Compared with the matching vehicle-treated controls, the higher doses of G and D and testosterone treatment significantly ( P < 0.05) lowered the TC and lipoprotein cholesterol levels. The greatest effect was observed regarding LDL-C in both Orx and IA males after G and D treatments, in which LDL-C decreased by more than 30%. The lower isoflavone doses induced a significant cholesterol-lowering effect ( P < 0.05) only in the Orx group. Like the estradiol treatment, the higher doses of G and D increased the TT levels in both rat models by more than 50% ( P < 0.05). The lower doses of isoflavones increased TT only in the Orx group. In male middle-aged rats, injections of higher doses of G and D decreased the serum cholesterol levels, as did testosterone injection, and brought about an increase in serum triglycerides similar to that observed after estradiol treatment.

Aggregation of soy protein-isoflavone complexes and gel formation induced by glucono-δ-lactone in soymilk

This study investigated the glucono-δ-lactone (GDL)-induced aggregation of isoflavones and soy proteins in soymilk. High-performance liquid chromatography (HPLC) analysis indicated that isoflavones mixed with β-conglycinin (7S) and glycinin (11S) proteins formed 7S-isoflavone and 11S-isoflavone complexes in soymilk supernatant fraction (SSF). Most of the soy protein-isoflavone complexes then precipitated into the soymilk pellet fraction (SPF) following the addition of 4 mM GDL, whereupon the pH value of the soymilk dropped from 6.6 to 5.9. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and HPLC analysis suggest that the addition of 4 mM GDL induced the aggregation of most 7S (α’, α and β subunits), 11S acidic and 11S basic proteins as well as isoflavones, including most aglycones, including daidzein, glycitein, genistein and a portion of glucosides, including daidzin, glycitin, genistin, malonyldaidzin and malonylgenistin. These results provide an important reference pertaining to the effects of GDL on the aggregation of soy protein-isoflavone complexes and could benefit future research regarding the production of tofu from soymilk.

Korean traditional Chungkookjang improves body composition, lipid profiles and atherogenic indices in overweight/obese subjects: a double-blind, randomized, crossover, placebo-controlled clinical trial

BACKGROUND/OBJECTIVES

Chungkookjang is a Korean representative fermented soybean food. In this study, we investigated the effect of Korean traditional Chungkookjang compared with placebo on body composition, dyslipidemia and risk factors for atherosclerosis in overweight/obese subjects.

SUBJECTS/METHODS

This double-blind, randomized, controlled crossover trial was conducted on 120 overweight/obese subjects, aged 19-29 years. Subjects were randomly divided into a Chungkookjang (n=60) or a placebo (n=60) group. After 12 weeks, the groups were crossed over for an additional 12 weeks. During the intervention period, subjects were asked to maintain their usual diet and activity and not to take any functional foods or dietary supplements. The anthropometric measures, lipid profiles and atherogenic indices were determined at baseline and at the end of each 12-week period.

RESULTS

The anthropometry measurements, percentage body fat, lean body mass, waist circumference and waist-to-hip ratio of women in the Chungkookjang group were significantly improved compared with the placebo group. Lipid profiles and high-sensitivity C-reactive protein of women in Chungkookjang were significantly improved. The atherogenic indices of apolipoprotein B/apolipoprotein A1 decreased in both the placebo and the Chungkookjang group, and it also decreased below 0.55 for all the men and women in the Chungkookjang group.

CONCLUSIONS

In conclusion, these results suggest that supplementation with Chungkookjang may improve body composition and risk factors for cardiovascular disease in overweight and obese adults.

The Soybean Peptide Vglycin Preserves the Diabetic β-cells through Improvement of Proliferation and Inhibition of Apoptosis

Replenishment of insulin-producing pancreatic β-cells would be beneficial in diabetes. The number of β-cells is maintained primarily by self-neogenesis to compensate for β-cell failure, loss or dedifferentiation. We present here a polypeptide vglycin, which was isolated and purified from germinating pea seeds. Vglycin exhibited positive effects in our diabetic models by promoting the proliferation and suppressing the apoptosis and dedifferentiation of β-cells. Vglycin promoted the restoration of β-cells in both young streptozotocin (STZ)-induced type 1 diabetic SD rats and in aged high-fat diet with (or without) STZ-induced type 2 diabetic C57BL/6 mice. We demonstrated that vglycin triggers this positive signaling by activating the insulin receptor and corresponding transcription factors. Impaired insulin sensitivity and glucose tolerance in aged T2DM mice were dramatically improved after long-term vglycin treatment, consistent with the altered level of inflammatory factor IL-1β/6. In addition, energy expenditure and body weights were significantly decreased in the mouse models after vglycin therapy. These results provide insight into the protective effects of vglycin on ameliorating β-cell function in standing glucolipotoxicity. Thus, vglycin may represent a new therapeutic agent for preventing and treating diabetes by replenishing endogenous insulin-positive cells.

Short-term hyperglycemia increases arterial superoxide production and iron dysregulation in atherosclerotic monkeys

The incidence and severity of atherosclerotic vascular disease are increased in diabetic patients, in part because of increased production of reactive oxygen species (ROS). Previously, we found both increased atherosclerosis and arterial protein oxidation 6 months after streptozotocin-induced diabetes in monkeys fed an atherogenic diet, the pattern of which was indicative of redox-active transition metal involvement. The goal of this study was to determine if short-term (1 month) hyperglycemia increases oxidative stress and dysregulates iron metabolism before differences in atherosclerosis. Cynomolgus monkeys with preexisting atherosclerosis were stratified by dietary history and plasma lipids and received either streptozotocin (STZ-DM; n = 10) or vehicle (control; n = 10). One month after diabetes induction, blood and artery samples were collected. There were no differences in plasma lipoprotein cholesterol, arterial cholesterol, and atherosclerosis between control and STZ-DM. However, plasma lipid peroxides were elevated 137% (P < .01); arterial superoxide was increased 47% (P < .05); plasma ferritin, an indicator of whole-body iron stores, was 46% higher (P < .05); and iron deposition within aortic atherosclerotic lesions was more prevalent in STZ-DM compared with controls. Arterial levels of the antioxidant enzymes, superoxide dismutase, catalase, and heme oxygenase-1 were not higher in STZ-DM, although superoxide was higher, suggesting impaired antioxidant response. The increase in ROS before differences in atherosclerosis supports ROS as an initiating event in diabetic vascular disease. Further studies are needed to determine if increases in iron stores and arterial iron deposition promote hydroxyl radical formation from superoxide and accelerate diabetic vascular damage.

Relationship between fractional pancreatic beta cell area and fasting plasma glucose concentration in monkeys

AIMS/HYPOTHESIS

We sought to establish the relationship between fasting plasma glucose concentrations and pancreatic fractional beta cell area in adult cynomolgus monkeys (Macaca fascicularis).

METHODS

Fasting plasma glucose and pancreatic fractional beta cell area were measured in 18 control and 17 streptozotocin-treated adult primates (17.0 +/- 1.2 vs 15.4 +/- 1.2 years old).

RESULTS

Fasting plasma glucose was increased (12.0 +/- 2.0 vs 3.4 +/- 0.1 mmol/l, p < 0.01) and fractional beta cell area was decreased (0.62 +/- 0.13% vs 2.49 +/- 0.35%, p < 0.01) in streptozotocin-treated monkeys. The relationship between fasting plasma glucose and pancreatic fractional beta cell area was described by a wide range of beta cell areas in controls. In streptozotocin-treated monkeys there was an inflection of fasting blood glucose at approximately 50% of the mean beta cell area in controls with a steep increase in blood glucose for each further decrement in beta cell area.

CONCLUSIONS/INTERPRETATION

In adult non-human primates a decrement in fractional beta cell area of approximately 50% or more leads to loss of glycaemic control.

Effects of soy vs. casein protein on body weight and glycemic control in female monkeys and their offspring

Nutritional interventions are important for reducing obesity and related conditions. Soy is a good source of protein and also contains isoflavones that may affect plasma lipids, body weight, and insulin action. Described here are data from a monkey breeding colony in which monkeys were initially fed a standard chow diet that is low fat with protein derived from soy. Monkeys were then randomized to a defined diet with a fat content similar to the typical American diet (TAD) containing either protein derived from soy (TAD soy) or casein-lactalbumin (TAD casein). The colony was followed for over two years to assess body weight, and carbohydrate and lipid measures in adult females (n=19) and their offspring (n=25). Serum isoflavone concentrations were higher with TAD soy than TAD casein, but not as high as when monkey chow was fed. Offspring consuming TAD soy had higher serum isoflavone concentrations than adults consuming TAD soy. Female monkeys consuming TAD soy had better glycemic control, as determined by fructosamine concentrations, but no differences in lipids or body weight compared with those consuming diets with TAD casein. Offspring born to dams consuming TAD soy had similar body weights at birth but over a two-year period weighed significantly less, had significantly lower triglyceride concentrations, and like adult females, had significantly lower fructosamine concentrations compared to TAD casein. Glucose tolerance tests in adult females were not significantly different with diet, but offspring eating TAD soy had increased glucose disappearance with overall lower glucose and insulin responses to the glucose challenge compared with TAD casein. Potential reasons for the additional benefits of TAD soy observed in offspring but not in adults may be related to higher serum isoflavone concentrations in offspring, presence of the diet differences throughout more of their lifespan (including gestation), or different tissue susceptibilities in younger animals.

Effects of soy protein and isoflavones on insulin resistance and adiponectin in male monkeys

Isoflavones may influence insulin action by means of their well-known receptor-mediated estrogenic activity. However, isoflavones also bind to peroxisome proliferator-activated receptors (PPARs) that are strongly associated with insulin action. Soy protein with its isoflavones has previously been shown to improve glycemic control in diabetic postmenopausal women and to improve insulin sensitivity in ovariectomized monkeys. The purpose of the current report was to extend our studies of dietary soy protein to male monkeys and determine effects of the soy isoflavones on insulin resistance. Two studies are reported here. Study one involved 91 male monkeys consuming 3 diets differing only by the source of protein (casein-lactalbumin, soy protein with a low isoflavone concentration, or soy protein with a high isoflavone concentration). Intravenous glucose tolerance tests were done, and plasma adiponectin and lipoprotein concentrations were determined after 25 months of study. Samples of visceral fat were obtained at 31 months for assessment of adiponectin and PPARgamma expression. The second study involved 8 monkeys in a Latin-square design that compared the effects of diets with casein/lactalbumin, soy protein with a high isoflavone concentration, or soy protein that was alcohol-washed to deplete the isoflavones. After 8 weeks of treatment, insulin sensitivity and plasma lipoproteins were assessed. At 10 weeks, a biopsy of the skeletal muscle was performed for determination of insulin receptor, PPARalpha, and PPARgamma content. The major findings were that consumption of isoflavone-containing soy protein dose-dependently increased insulin responses to the glucose challenge and decreased plasma adiponectin, whereas isoflavone-depleted soy protein decreased body weight and had no effect on plasma adiponectin concentrations. Muscle PPARalpha and gamma expression was also increased with the isoflavone-depleted soy relative to either casein or soy protein containing the isoflavones. Further studies are needed to determine the mechanisms involved in these effects of a high-soy isoflavone diet and to optimize dietary isoflavone content for maximal health benefits in male subjects.

Hypocholesterolemic effects of dietary soybean vs. casein proteins in a crossed over diets in rat

To investigate the effects of dietary proteins on the level of serum total cholesterol (TC), triglyceride (TG) and high density lipoprotein (HDL), 32 male Wistar rats were randomly divided in control and 3 experimental groups (El, E2 and E3). The feeding regimes of rats were as follow: control, standard diet; E1, a cholesterol free diet containing 20% soybean protein; E2, a cholesterol free diet containing 20% casein and E3, a cholesterol free diet containing 10% soybean protein and 10% casein. The experimental period was 11 weeks but at the end of 7th week the diets of E1 and E2 groups were crossed over for the next 4 weeks. Blood samples were collected weekly, via the ophthalmic sinus and the serum levels TC, TG and HDL were measured. In comparison with control group, the results show that at the end of 7th week TC levels in E1 and E2 groups were significantly (p<0.05) increased while HDL level unchanged and the TC value of E2 was bigger (not significant) than E1. However by crossing over the diets, the TC level was significantly (p<0.05) diminished in E2 while TG value remarkably (p<0.05) increased. These results indicate that soybean protein may insert its hypocholesterolemic effect in hypercholestrolemic condition than in normolipidemic condition.

Methods for nutrigenomics and longevity studies in Drosophila: effects of diets high in sucrose, palmitic acid, soy, or beef

Nutrigenomics is the study of gene-nutrient interactions and how they affect the health and metabolism of an organism. Combining nutrigenomics with longevity studies is a natural extension and promises to help identify mechanisms whereby nutrients affect the aging process, life span, and, with the incorporation of age-dependent functional measures, health span. The topics we discuss in this chapter are genetic techniques, dietary manipulations, metabolic studies, and microarray analysis methods to investigate how nutrition affects gene expression, life span, triglyceride levels, total protein levels, and live weight in Drosophila. To better illustrate nutrigenomic techniques, we analyzed Drosophila larvae or adults fed control diets (high sucrose) and compared these with larvae or adults fed diets high in the saturated fat palmitic acid, soy, or 95% lean ground beef. The main results of these studies are, surprisingly, that triglyceride and total protein levels are significantly decreased by the beef diet in all adults, and total protein levels are significantly increased in male flies fed the soy diet. Furthermore, and less surprisingly, we found that all three experimental diets significantly decreased longevity and increased the length of time to develop from egg to adult. We also describe preliminary microarray results with adult flies fed the different diets, which suggest that only about 2-3% of the approx 18,000 genes have significantly altered mRNA expression levels compared with flies fed a control sucrose diet. The significance of these results and other types of nutrigenomics and longevity analyses is discussed.

Hyperglycemia and loss of ovarian hormones mediate atheroma formation through endothelial layer disruption and increased permeability

The overall goal of this project was to examine the interactions of hyperglycemia and loss of ovarian hormones on the artery wall in a type I diabetic mouse model. Intact or ovariectomized (OVX) female BALB/C mice were fed a high-cholesterol diet. Half the animals were treated with steptozotocin to induce insulin-deficient diabetes mellitus, generating four treatment groups: control, intact; control, ovariectomized; diabetic, intact; diabetic, ovariectomized (DOVX). We examined arterial structure and function and found that 1) diabetes and ovariectomy additively increased endothelial layer permeability, 2) arterial stiffening was increased in DOVX, 3) DOVX synergistically increased atheroma formation, and 4) ultrastructural evaluation revealed that the basal lamina was often multilayered and formed convoluted aggregates separating endothelium from the internal elastic lamina in diabetic, but not control arteries or arteries from OVX mice. Endothelium overlying these regions formed thin cytoplasmic extensions between these aggregates and was often separated from the basal lamina by electron lucent spaces. Our studies showed that diabetes and loss of ovarian function have additive and synergistic effects to worsen arterial pathophysiology by disrupting the arterial endothelial layer with increased permeability and increased atheroma formation.

Phytoestrogens: end of a tale?

Phytoestrogens are plant-derived hormone-like diphenolic compounds of dietary origin that are present at high levels in plasma of subjects living in areas with low atherosclerosis and cancer incidence. The term phytoestrogen is commonly applied to the soy isoflavones genistein, daidzein and glycitein. As outlined in a previous review article in this journal by Adlercreutz and Mazur 1, these compounds are weakly estrogenic and appear to influence the cardiovascular system, the production, metabolism and biological activity of sex-hormones, as well as malignant cell proliferation, differentiation and angiogenesis. Recently skepticism has developed concerning the true potential of phytoestrogens to beneficially modify these processes. A critical analysis of the early findings from supplementing the diet with soy protein has failed to confirm phytoestrogens as the responsible agent for beneficial cardiovascular effects, be it by way of lipid reduction, vasodilation or lipoprotein oxidation. Furthermore, contrasting data have been reported on the potential of phytoestrogens to prevent hormone-dependent cancers (e.g. breast and prostate) and to successfully treat post-menopausal complaints, an indication for which they are widely used. These potentially negative findings have led health authorities in several countries to suggest maximum daily intake levels for phytoestrogens. There is now growing interest in the use of soy products containing low levels of phytoestrogens and in research on other phytoestrogen free legumes such as lupin.

Soy proteins reduce progression of a focal lesion and lipoprotein oxidiability in rabbits fed a cholesterol-rich diet

The effects of different dietary proteins on the progression of a focal atheromatous lesion and on lipoprotein oxidiability were studied in male New Zealand rabbits. Focal lesions were induced on common carotid arteries by applying an electric current, using a bipolar microcoagulator. After surgery, animals were fed for 90 days two different diets, both with 1% cholesterol, 15% saturated fatty acids and 20% protein: the protein source was constituted in one group (SOY) by 16% soy protein isolate plus 4% milk whey proteins, in the other (CASEIN) by 16% casein plus 4% milk whey proteins. Lower levels of plasma cholesterol and triglycerides (-47 and -65%, respectively) (P < 0.05) were detected in the SOY versus the CASEIN group at the end of treatment. Cryosection analyses of the carotids, indicated a highly significant reduction (-39%; P < 0.05) in the focal lesion progression in the SOY versus the CASEIN group. Copper-mediated oxidation of low-density lipoprotein (LDL) from rabbits fed the two different diets, performed in vitro by analysis of conjugated diene formation, showed a significantly longer lag phase in the SOY (150 +/- 5 min) versus the CASEIN animals (20 +/- 3 min) (P < 0.05). These data, while confirming the well-known lipid lowering properties of soy proteins, indicate, in this animal model, a remarkable activity on a focal atheromatous lesion, possibly also linked to a powerful antioxidant activity.

Soy Protein With Isoflavones, but not an Isoflavone-Rich Supplement, Improves Arterial Low-Density Lipoprotein Metabolism and Atherogenesis

OBJECTIVE

We sought to determine if arterial LDL metabolism contributes to the decreased atherosclerosis seen with soy and if isolated isoflavones would have similar effects.

METHODS AND RESULTS

Ovariectomized monkeys were fed an atherogenic diet for 20 weeks with a protein source of (1) casein/lactalbumin (CAS, n=20), (2) soy protein isolate (SOY, n=20), or (3) casein/lactalbumin with isolated soy isoflavones (ISO, n=17). Plasma lipoprotein concentrations were improved with SOY but not ISO. Arterial LDL metabolism was characterized with one subset (n=12/group) injected with dual-labeled tyramine-cellobiose (TC)-LDL (125I-TC-131I-LDL) 24 hours before necropsy to determine LDL degradation and accumulation, while another subset (n=8/group) was injected with 125I-TC-LDL 1 hour before necropsy to determine LDL permeability and delivery.

CONCLUSIONS

Coronary artery LDL degradation was reduced by 50% (P=0.02) with SOY but not with ISO compared with CAS. Neither treatment altered arterial permeability. Reduced LDL degradation with SOY was due to decreased arterial LDL delivery (P=0.02). Carotid artery cholesterol ester was also decreased with SOY, but not with ISO. Plasma isoprostanes or plasma markers of inflammation did not differ among treatment groups. Thus, the decreased arterial LDL delivery and subsequent LDL degradation may explain, in part, the atheroprotective effects of soy.

Soy protein with or without isoflavones, soy germ and soy germ extract, and daidzein lessen plasma cholesterol levels in golden Syrian hamsters

Dietary isolated soy protein (ISP, containing approximately equal amounts of daidzein and genistein), ethanol-extracted ISP (ISP (-)), soygerm or soygerm extract (containing large amounts of daidzein and glycitein and little genistein) and the isoflavone, daidzein, were hypothesized to lessen plasma cholesterol in comparison with casein. Sixty male and 60 female golden Syrian hamsters (6-8 weeks of age) were randomly assigned to six treatments fed for 10 weeks. Four of the experimental diets (ISP, daidzein, soygerm, and soygerm extract) contained 1.3 mmol total isoflavones/kg. The ISP (-) diet contained 0.013 mmol isoflavone/kg, whereas the casein diet contained no isoflavones. Hamsters fed ISP, ISP (-), daidzein, soygerm, and soygerm extract had significantly less plasma total cholesterol (by 16%-28%), less non-HDL cholesterol (by 15%-50%) and less non-HDL/HDL cholesterol ratios compared with hamsters fed casein (P < 0.01). For male hamsters, there were no differences among treatments in plasma HDL concentrations. Female hamsters fed ISP (-) had significantly greater HDL levels (P < 0.01) than females fed casein or daidzein. Triglyceride concentration was significantly less in hamsters fed ISP (-) compared with the casein-fed females. Because soy protein with or without isoflavones, soygerm and soygerm extract, and daidzein lessened plasma cholesterol to an approximately equal extent, soy protein alone, varying mixtures of isoflavones, and other extractable components of soy are responsible for cholesterol-lessening effects of soy foods, mainly due to their effects to lessen LDL cholesterol.

Soy foods and soybean isoflavones and menopausal health

Soybeans are a natural dietary source of isoflavones, which have estrogen-like properties. Therefore, it is worthwhile to consider the implications for soy of the recently published findings of the Heart and Estrogen/Progestin Replacement Study (HERS) I/II and the Women's Health Initiative (WHI). The WHI found coronary heart disease (CHD) risk to be increased in women receiving hormone replacement therapy, and both studies found increases in venous thromboembolic disease in such women. Additionally, stroke and breast cancer risk were increased in the WHI, although risk of colorectal cancer and fracture was decreased. Because research suggests that it is the combination of estrogen plus progestin, and not estrogen alone, that increases breast cancer risk, soy seems unlikely to increase risk because it has no progestin activity. Similarly, there is no evidence to suggest that soy will increase venous thromboembolic disease or stroke; however, only limited data are available in this area. There are promising data suggesting that soy may decrease CHD risk, although studies conducted thus far have examined only markers of risk and not actual CHD events. Similarly, short-term studies generally suggest that soy reduces bone loss in postmenopausal women; however, such effects have been noted primarily only at the spine, and longer-term studies are needed. Finally, very limited human research suggests that soy may decrease colon cancer risk, but this is highly speculative. The results of HERS I/II and WHI suggest that soy may have some of the advantages, but not the disadvantages, of combined hormone replacement therapy (at least with respect to the specific hormones and doses used in the HERS I/II and WHI), but that large, long-term intervention studies examining disease outcome are needed before definitive conclusions can be drawn. Nevertheless, the evidence warrants recommendations that menopausal women include soy in their diets.

Beneficial effects of soy phytoestrogen intake in postmenopausal women with type 2 diabetes

OBJECTIVE

Phytoestrogen consumption has been shown to reduce risk factors for cardiovascular disease. Type 2 diabetes confers an adverse cardiovascular risk profile particularly in women after menopause. The aim of this study was to determine whether a dietary supplement with soy protein and isoflavones affected insulin resistance, glycemic control, and cardiovascular risk markers in postmenopausal women with type 2 diabetes.

RESEARCH DESIGN AND METHODS

A total of 32 postmenopausal women with diet-controlled type 2 diabetes completed a randomized, double blind, cross-over trial of dietary supplementation with phytoestrogens (soy protein 30 g/day, isoflavones 132 mg/day) versus placebo (cellulose 30 g/day) for 12 weeks, separated by a 2-week washout period.

RESULTS

Compliance with the dietary supplementation was >90% for both treatment phases. When compared with the mean percentage change from baseline seen after 12 weeks of placebo, phytoestrogen supplementation demonstrated significantly lower mean values for fasting insulin (mean +/- SD 8.09 +/- 21.9%, P = 0.006), insulin resistance (6.47 +/- 27.7%, P = 0.003), HbA(1c) (0.64 +/- 3.19%, P = 0.048), total cholesterol (4.07 +/- 8.13%, P = 0.004), LDL cholesterol (7.09 +/- 12.7%, P = 0.001), cholesterol/HDL cholesterol ratio (3.89 +/- 11.7%, P = 0.015), and free thyroxine (2.50 +/- 8.47%, P = 0.004). No significant change occurred in HDL cholesterol, triglycerides, weight, blood pressure, creatinine, dehydroepiandrosterone sulfate, androstenedione, and the hypothalamic-pituitary-ovarian axis hormones.

CONCLUSIONS

These results show that dietary supplementation with soy phytoestrogens favorably alters insulin resistance, glycemic control, and serum lipoproteins in postmenopausal women with type 2 diabetes, thereby improving their cardiovascular risk profile.

Risks and benefits of soy phytoestrogens in cardiovascular diseases, cancer, climacteric symptoms and osteoporosis

Phytoestrogens, plant chemicals classified as isoflavones, coumestans and lignans, display estrogen-like activity because of their structural similarity to human estrogens and exhibit high affinity binding for the estrogen receptor beta. They are common components of food items such as grains, beans, fruits and nuts. Isoflavones are primarily found in soybeans and foods made from soy. In particular, significant therapeutic properties have been generally attributed to soy isoflavones, but most of the claims have been poorly, or not at all, confirmed by well designed clinical trials. Such is the case of the purported role of soy isoflavones in reducing plasma cholesterol levels. This link is now not supported by many authors or by appropriately designed clinical studies. The role of isoflavones in cancer prevention, particularly of tumours under endocrine control (breast, prostate and others) is again only supported by weak to nonexisting clinical evidence. A similarcase is that of the prevention/treatment of postmenopausal symptoms and osteoporosis. Disturbing data have been reported on potential negative effects of soy isoflavones on cognitive function in the aged, particularly relating to tofu intake. Recent studies have finally indicated a potential role for soy isoflavones in inducing chromosomal changes in cells exposed in vitro and potentiating chemical carcinogens. These findings may not, however, be extrapolated to clinical conditions. Available data do not appear to unequivocally support beneficial effects of soy isoflavones, and warn against their wide use, in the absence of satisfactory clinical findings.