Influence of ethnic origin (Asian v. Caucasian) and background diet on the bioavailability of dietary isoflavones

Traditional and Domestic Cooking Dramatically Reduce Estrogenic Isoflavones in Soy Foods

Soybean is a pulse which has considerable nutritional value due to its high protein, fibers and polyunsaturated fatty acid (PUFA) contents. It also contains phytoestrogenic compounds that definitely hinder its recommendation for general consumption. Contrary to ancient times, when soybeans were boiled, modern commercial soy foods can contain up to 150 mg/100g of estrogenic isoflavones. Interestingly, current estimations of isoflavone intake in the literature do not distinguish between the origins of soy food, i.e., whether it is homemade or commercial. As a result, the isoflavone exposure in Asian countries may well be overestimated. This study aims to demonstrate, based on step-by-step monitoring of isoflavones, that traditional and domestic treatments, leveraging isoflavones water-solubility, can indeed significantly reduce their content in soy foods. Indeed, when compared to commercial foods, the isoflavone content was found to be 20, 2.6, 4.5 and 9.8 times lower in "homemade" soy juice, tofu, tempeh and miso, respectively. Additionally, water soaking was found to reduce the isoflavones levels in soy-textured proteins by more than 70%. Hence, this simple process has the potential to help drastically reduce overall xenoestrogens exposure. This study could serve as a basis for establishing the isoflavones Reference Dose and issuing food safety guidelines.

Effect of soy isoflavone supplementation on blood pressure: a meta-analysis of randomized controlled trials

BACKGROUND

Previous experimental studies have suggested that the consumption of soy isoflavones may have a potential impact on lowering blood pressure. Nevertheless, epidemiological studies have presented conflicting outcomes concerning the correlation between soy isoflavone consumption and blood pressure levels. Consequently, a comprehensive meta-analysis of all eligible randomized controlled trials (RCTs) was conducted to explore the influence of soy isoflavones on systolic blood pressure (SBP) and diastolic blood pressure (DBP) in adults.

METHODS

A thorough search of PubMed, Embase, and the Cochrane Library for relevant literature up to April 30, 2023 was conducted. RCTs involving adults that compared soy isoflavone supplementation with a placebo (the same matrix devoid of soy isoflavone) were included. The combined effect size was presented as the weighted mean difference (WMD) along with 95% confidence interval (CI), employing a fixed-effects model.

RESULTS

Our meta-analysis included a total of 24 studies involving 1945 participants. The results revealed a significant reduction in both SBP and DBP with soy isoflavone supplementation. Subgroup analyses suggested more pronounced reductions in SBP and DBP for interventions lasting ≥6 months, in individuals receiving mixed-type soy isoflavone, and among patients with metabolic syndrome or prehypertension. However, we did not detect significant nonlinear associations between supplementation dosage and intervention duration concerning both SBP and DBP. The overall quality of evidence was deemed moderate.

CONCLUSIONS

The current meta-analysis revealed that supplementation with soy isoflavones alone effectively reduces blood pressure. Additional high-quality studies are required to investigate the efficacy of blood pressure reduction through supplementation with an optimal quantity and proportion of soy isoflavone.

Intake of legumes and cardiovascular disease: A systematic review and dose-response meta-analysis

AIMS

To summarize the evidence on the association between the intake of legumes and the risk of cardiovascular disease (CVD) overall, coronary heart disease (CHD) and stroke, and to identify optimal intake levels for reduced disease risk through a systematic review and dose-response meta-analysis.

DATA SYNTHESIS

We have systematically searched PubMed, Scopus and Web of Science up to March, 2022 for the retrieval of intervention and observational studies (PROSPERO Reg. number: CRD42021247565). Pooled relative risks (RRs) comparing extreme categories of intake were computed using random-effects models. One-stage dose-response meta-analyses were also performed using random-effects models. 22 831 articles were screened resulting in 26 eligible observational studies (21 prospective cohort and 5 case-control studies). When comparing extreme categories of intake, the consumption of legumes was inversely associated with CVD (n = 25: RR = 0.94; 95%CI:0.89,0.99) and CHD (n = 16: RR = 0.90; 95%CI:0.85,0.96), but not with stroke (n = 9: RR = 1.00; 95%CI:0.93,1.08). We further found evidence for an inverse dose-response association with CHD, increasing in magnitude up to an intake of 400 g/week, after which the benefit seems to level-off.

CONCLUSIONS

The intake of legumes was associated with a reduced risk of CVD and CHD, but not with stroke, among individuals with the highest consumption levels. An intake level of 400 g/week seemed to provide the optimal cardiovascular benefit. Further research is needed to better understand the role of legumes in stroke subtypes.

Systematic Review of the Impact of Genistein on Diabetes Related Outcomes

Diabetes is the 8th leading cause of death in the world and the prevalence is rising in low-income countries. Cardiovascular diseases are the leading cause of death worldwide, especially for individuals with diabetes. While medications exist to treat symptoms of diabetes, lack of availability and high costs may deter their use by individuals with low incomes as well as those in low-income nations. Therefore, this systematic review was performed to determine whether genistein, a phytoestrogen found in soy products, could provide therapeutic benefits for individuals with diabetes. We searched PubMed and SCOPUS using the terms 'genistein', 'diabetes', and 'glucose' and identified 33 peer-reviewed articles that met our inclusion criteria. In general, preclinical studies demonstrated that genistein decreases body weight and circulating glucose and triglycerides concentrations while increasing insulin levels and insulin sensitivity. Genistein also delayed the onset of type 1 and type 2 diabetes. In contrast, clinical studies utilizing genistein generally reported no significant relationship between genistein and body mass, circulating glucose, A1C concentrations, or onset of type 1 diabetes. However, genistein was found to improve insulin sensitivity and serum triglyceride concentrations and delayed the onset of type 2 diabetes. In summary, preclinical and clinical studies suggest that genistein may help delay the onset of type 2 diabetes and improve several symptoms associated with the disease. Although additional research is required to confirm these findings, the results highlighted in this review provide some evidence that genistein may offer a natural approach to mitigating some of the complications associated with diabetes.

Soy isoflavones prevent bone resorption and loss, a systematic review and meta-analysis of randomized controlled trials

BACKGROUND

Osteoporosis is a common bone disease characterized by reduced bone mass resulting from continuous bone resorption.

METHODS

PubMed, Scopus, and Embase were searched to find published trials on the effect of soy isoflavones on bone mineral density (BMD) and bone turnover markers (bone-specific alkaline phosphatase, osteocalcin, osteoprotegerin, pyridinoline, deoxypyridinoline, C-telopeptide, and N-telopeptide). Random-effects inverse-variance model was used to calculate the pooled effects.

RESULTS

A total of 5313 articles were found, screened, and assessed for eligibility, and finally 52 trials were included in the meta-analysis. Consumption of soy isoflavones caused significant improvement in BMD of lumbar spine (mean difference (MD) = 0.76%; 95% CI: 0.09, 1.42%; p = 0.03), hip (MD = 0.22%; 95% CI: 0.02, 0.42%; p = 0.04), and femoral neck (MD = 2.27%; 95% CI: 1.22, 3.31%; p < 0.001). Subgroup analysis showed that in all 3 sites, the improvement was significant in normal weight subjects and interventions longer than a year, although trial location and dosage were also factors influencing isoflavones' impact on BMD. Among markers of bone turnover, osteoprotegerin (MD = 5.79; 95% CI: 3.08, 8.51 pg/ml; p < 0.001), pyridinoline (MD = -5.13; 95% CI: -7.76, -2.50 nmol/mmol; p < 0.001), and C-telopeptides (MD = -0.08; 95% CI: -0.16, -0.00 ng/ml; p = 0.04) were favorably affected by isoflavones while osteocalcin and bone alkaline phosphatase did not change. Subgroup analysis of bone markers showed that in overweight/obese individuals and dosages <90 mg/day, isoflavones are more effective.

CONCLUSIONS

Soy isoflavones prevent osteoporosis-related bone loss in any weight status or treatment duration. They increase BMD in normal weight subjects and diminish bone resorption in overweight/obese individuals. Although bone resorption may be decelerated over short-term isoflavone consumption, periods longer than a year are probably needed to affect BMD. Isoflavones also appear benefits on bone in any dose or subjects' ethnicity.

Beyond the Cholesterol-Lowering Effect of Soy Protein: A Review of the Effects of Dietary Soy and Its Constituents on Risk Factors for Cardiovascular Disease

The hypocholesterolemic effect of soy is well-documented and this has led to the regulatory approval of a health claim relating soy protein to a reduced risk of cardiovascular disease (CVD). However, soybeans contain additional components, such as isoflavones, lecithins, saponins and fiber that may improve cardiovascular health through independent mechanisms. This review summarizes the evidence on the cardiovascular benefits of non-protein soy components in relation to known CVD risk factors such as hypertension, hyperglycemia, inflammation, and obesity beyond cholesterol lowering. Overall, the available evidence suggests non-protein soy constituents improve markers of cardiovascular health; however, additional carefully designed studies are required to independently elucidate these effects. Further, work is also needed to clarify the role of isoflavone-metabolizing phenotype and gut microbiota composition on biological effect.

Soy Food Intake and Biomarkers of Breast Cancer Risk: Possible Difference in Asian Women?

Soy foods may protect against breast cancer in Asian but not in Western populations. We examined if the levels of various markers of breast cancer risk and inflammation, as well as the effects of soy food consumption on these markers, differ between Asian and non-Asian premenopausal women in two soy intervention trials. One study randomized 220 women to a 2-yr intervention and the other one randomized 96 women in a crossover design to examine the effects of consumption of 2 daily soy servings on nipple aspirate fluid (NAF) volume; estrogens in serum, NAF, and urine; insulin-like growth factor-1 (IGF-1), IGF-binding protein 3, and inflammatory markers in serum; and mammographic densities. Mixed linear models were applied to assess ethnic differences in biomarkers and response to the soy diet. Serum C-reactive protein, serum leptin, NAF volume, and NAF estrone sulfate were lower, while urinary isoflavones were higher in Asian than in non-Asian women. A significant interaction (p_interaction = 0.05) between ethnicity and soy diet was observed for IGF-1 but not for other biomarkers. The current findings suggest possible ethnic differences in levels of biomarkers for breast cancer risk but little evidence that Asian women respond differently to soy foods than non-Asian women.

Prevalence and severity of menopause symptoms and associated factors across menopause status in Korean women

OBJECTIVE

The present study investigated the prevalence and severity of menopause symptoms experienced by Korean women aged 44 to 56 years and their associated factors.

METHODS

A cross-sectional study was performed on 2,201 women aged 44 to 56 years in health checkup centers between November 2012 and March 2013. The 29-item Menopause-Specific Quality of Life Questionnaire was used to assess vasomotor, psychosocial, physical, and sexual symptoms related to menopause. The guidelines for the classification of reproductive aging stages proposed at the Stages of Reproductive Aging Workshop were used. Multivariable linear regression analyses were performed to identify factors associated with severity of menopause symptoms.

RESULTS

Among participants, 42.6% were premenopausal, 36.7% were perimenopausal, and 20.7% were postmenopausal. Although physical symptoms were the most severe menopause symptoms experienced by premenopausal and perimenopausal women, postmenopausal women reported sexual symptoms as the most bothersome. The mean scores for each domain increased from the premenopausal period through the postmenopausal period (P for trend < 0.001). The regression model revealed that age (for vasomotor and sexual symptoms) and obesity (for vasomotor and physical symptoms) were significantly associated with severity of menopause symptoms (P < 0.05). Physically active women had fewer severe physical symptoms related to menopause than inactive women.

CONCLUSIONS

Postmenopausal women experience the most severe symptoms. Obesity and physical activity are the main modifiable factors associated with symptom severity. Further studies are needed to examine the effects of physical activity promotion and weight control interventions on preventing menopause symptoms in Korean women.

Dietary Pattern Trajectories from 6 to 12 Months of Age in a Multi-Ethnic Asian Cohort

Little is known about the dietary patterns of Asian infants in the first year of life, nor of their associations with maternal socio-demographic factors. Based on the Growing Up in Singapore towards healthy Outcomes (GUSTO) mother-offspring cohort, cross-sectional dietary patterns were derived by factor analysis using 24-h recalls and food diaries of infants at 6-, 9- and 12-months of age. Dietary pattern trajectories were modeled by mapping similar dietary patterns across each age using multilevel mixed models. Associations with maternal socio-demographic variables, collected through questionnaires during pregnancy, were assessed using general linear models. In n = 486 infants, four dietary pattern trajectories were established from 6- to 12-months. Predominantly breastmilk: mainly breastmilk and less formula milk,

GUIDELINES

rice porridge, vegetables, fruits and low-fat fish and meat, Easy-to-prepare foods: infant cereals, juices, cakes and biscuits and Noodles (in soup) and seafood: noodle and common accompaniments. In adjusted models, higher maternal education attainment was correlated with higher start scores on Predominantly breastmilk, but lowest education attainment increased its adherence over time. Older mothers had higher start scores on Easy-to-prepare foods, but younger mothers had increased adherence over time. Chinese mothers had higher start scores on Predominantly breastmilk but greater adherence to GUIDELINES over time, while Indian mothers had higher start scores on Easy-to-prepare foods but greater adherence to Predominantly breastmilk with time (p < 0.05 for all). Changes in trajectories over time were small. Hence, dietary patterns established during weaning are strongly influenced by maternal socio-demographic factors and remain stable over the first year of life.

Perinatal exposure to genistein affects the normal development of anxiety and aggressive behaviors and nitric oxide system in CD1 male mice

Genistein is a phytoestrogen, particularly abundant in soybeans, that is able to bind estrogen receptors exerting both estrogenic and antiestrogenic activities. Genistein is largely present in the human diet even during pregnancy. Embryos and fetuses are therefore, commonly exposed to genistein during the development and after birth. In the present study, we used a murine model as a test end-point to investigate the effects of early exposure to genistein on adult male behavior and related neural circuits. Daily exposure of dams to genistein (100 μg/g of body weight) during late pregnancy and early lactation, produced in male offspring, when adults, significant changes in anxiety and aggressive behaviors. Moreover, we found statistically significant variations in the number of neuronal nitric-oxide synthase positive cells in the amygdala. In conclusions, these data indicate that early exposure to phytoestrogens may induce life-long effects on the differentiation of brain structures and behaviors.

Interactions of isoflavones and other plant derived estrogens with estrogen receptors for prevention and treatment of breast cancer-considerations concerning related efficacy and safety

Phytoestrogens are natural endocrine disruptors that interfere with estrogenic pathways. They insert directly within the hormone-binding domain of ERα and β, with a preference for the β isoform of which the concentration predominates in the normal mammary epithelium. Since ERβ antagonizes the growth promoting effect of ERα, which is mainly expressed in estrogen-sensitive tumor cells, a potential protective action against breast cancer incidence has been ascribed to phytoestrogens. The fact that Asian women living in far-east countries who consume isoflavone-rich food are less subjected to breast cancer emergence than their congeners in the USA as well as Caucasian women has been advocated to justify such a concept. Overview of data concerning the mechanism of action phytoestrogens reveals that such a view is an oversimplification: Such compounds interfere with a huge panel of regulatory proteins, giving rise to both promoting and antagonizing carcinogenic effects. Moreover, various physiological and pathological factors able to amplify these effects are not often sufficiently taken into account, which increases the difficulty to interpret data. Nevertheless, this overview of data established that chemical structures and concentrations modulate such effects: at the micromolar level, isoflavones activate ERα-mediated transcription and breast cancer cell proliferation while flavones fail to induce any significant promoting effects. At higher doses, both classes of compounds may display an antitumor activity. Reasons for such distinct behaviors as well as their potential impact in therapeutic applications are analyzed here. Ability of isoflavones and flavones to antagonize the association of calmodulin to ERα, which is required for its enhanced transcriptional activity is evoked to justify the antitumor activity ascribed to some flavones. Finally, a suspicion that peculiar classes of phytoestrogens may adopt a SERM-like conformation is addressed in a context of selection and synthesis of compounds with non-equivocal therapeutic value. This article is part of a Special Issue entitled "Phytoestrogens".

Bioavailability of glycitein relatively to other soy isoflavones in healthy young Caucasian men

Glycitein is a Selective Estradiol Receptor Modulator (SERM) from soy. The study reports plasma bioavailability and urine excretion of glycitein compared to other soy isoflavones after a unique intake of food supplement based on soy germ containing 55.24mg isoflavones. Eighteen plasma and urinary sampling profiles collected over 48h from healthy young Caucasian men were analysed using specific ELISAs. Eight profiles contained equol. Glycitein T(max), C(max), AUC(0→24h) and T(½) in plasma were calculated. Urine T(max), % of excretion at 24h and clearance were assessed. Glycitein is one of the best absorbed flavonoids. Plasma steady-state level can be achieved by several intakes a day. Glycitein bioavailability is similar to that of daidzein and its urinary excretion is significantly higher than that of genistein. Equol does not affect glycitein bioavailability. Knowing glycitein bioavailability in man is essential for the development of soy-germ-based food supplements for health applications.

The role of soy isoflavones in menopausal health: report of The North American Menopause Society/Wulf H. Utian Translational Science Symposium in Chicago, IL (October 2010)

OBJECTIVES

If and to what extent soy protein, soy isoflavones, and their metabolites, including S(--)-equol, have beneficial effects on women's health is currently unclear. The North American Menopause Society (NAMS)/Utian Translational Science Symposium on Soy and Soy Isoflavones convened October 9-10, 2010, to clarify basic and clinical research findings as they relate to the risk and benefits of soy products for peri- and postmenopausal women.

METHODS

A working group of faculty and panelists composed of clinical and research experts in the fields of women's health and botanicals met during a 2-day translational symposium to cover the latest evidence-based science on isoflavones as they affect menopausal symptoms, breast and endometrial cancer, atherosclerosis, bone loss, and cognition. Full descriptions of the bioavailability and pharmacokinetics of isoflavones were also presented. Subspecialty groups then broke off with the goal of translating the information into a report for general medical practice and identifying further research areas. All faculty and panelists reviewed the final report, which was then approved by the NAMS Board of Trustees.

RESULTS

From the hundreds of studies reviewed in this report, there are mixed results of the effects on midlife women. Soy-based isoflavones are modestly effective in relieving menopausal symptoms; supplements providing higher proportions of genistein or increased in S(--)-equol may provide more benefits. Soy food consumption is associated with lower risk of breast and endometrial cancer in observational studies. The efficacy of isoflavones on bone has not been proven, and the clinical picture of whether soy has cardiovascular benefits is still evolving. Preliminary findings on cognitive benefit from isoflavone therapy support a "critical window" hypothesis wherein younger postmenopausal women derive more than older women.

CONCLUSIONS

Several areas for further research have been identified on soy and midlife women. More clinical studies are needed that compare outcomes among women whose intestinal bacteria have the ability to convert daidzein to equol (equol producers) with those that lack that ability (equol nonproducers) in order to determine if equol producers derive greater benefits from soy supplementation. Larger studies are needed in younger postmenopausal women, and more research is needed to understand the modes of use of soy isoflavone supplements in women. The interrelations of other dietary components on soy isoflavones consumed as a part of diet or by supplement on equol production also require further study, as do potential interactions with prescription and over-the-counter medications. And finally, greater standardization and documentation of clinical trial data of soy are needed.