Effects of Equol Supplement on Bone and Cardiovascular Parameters in Middle-Aged Japanese Women: A Prospective Observational Study

Production of equol, dehydroequol, 5-hydroxy-equol and 5-hydroxy-dehydroequol in soy beverages by the action of dihydrodaidzein reductase in Limosilactobacillus fermentum strains

Equol and 5-hydroxy-equol, and their analogous compounds dehydroequol and 5-hydroxy-dehydroequol, are bioactive isoflavones formed by microbial metabolism. The aims of this work were to elucidate the formation of dehydroequol and 5-hydroxy-dehydroequol, to identify the role of dihydrodaidzein reductase (DHDR) in the production of equol, dehydroequol, 5-hydroxy-equol and 5-hydroxy-dehydroequol and to develop soy beverages enriched in these compounds through engineered lactic acid bacteria. DHDR was responsible for the production of equol and dehydroequol from dihydrodaidzein (DHD), and of 5-hydroxy-equol and 5-hydroxy-dehydroequol from dihydrogenistein (DHG), even in the absence of tetrahydrodaidzein reductase (THDR). The combination of DHDR with dihydrodaidzein racemase (DDRC), and/or THDR, allowed the production of soy beverages enriched in equol (241.34 ± 34.56 μM), dehydroequol (31.23 ± 5.78 μM), 5-hydroxy-equol (125.54 ± 7.90 μM) and 5-hydroxy-dehydroequol (292.34 ± 14.67 μM). Beverages fortified with high concentrations of equol, 5-hydroxy-dehydroequol and 5-hydroxy-equol could provide significant health benefits for consumers.

Polyphenol-Derived Microbiota Metabolites and Cardiovascular Health: A Concise Review of Human Studies

Polyphenols, plant-derived secondary metabolites, play crucial roles in plant stress responses, growth regulation, and environmental interactions. In humans, polyphenols are associated with various health benefits, particularly in cardiometabolic health. Despite growing evidence of polyphenols' health-promoting effects, their mechanisms remain poorly understood due to high interindividual variability in bioavailability and metabolism. Recent research highlights the bidirectional relationship between dietary polyphenols and the gut microbiota, which can influence polyphenol metabolism and, conversely, be modulated by polyphenol intake. In this concise review, we summarized recent advances in this area, with a special focus on isoflavones and ellagitannins and their corresponding metabotypes, and their effect on cardiovascular health. Human observational studies published in the past 10 years provide evidence for a consistent association of isoflavones and ellagitannins and their metabotypes with better cardiovascular risk factors. However, interventional studies with dietary polyphenols or isolated microbial metabolites indicate that the polyphenol-gut microbiota interrelationship is complex and not yet fully elucidated. Finally, we highlighted various pending research questions that will help identify effective targets for intervention with precision nutrition, thus maximizing individual responses to dietary and lifestyle interventions and improving human health.

Effect of Fermented Soy Beverage on Equol Production by Fecal Microbiota

Soy consumption is associated with health benefits, mainly linked to the ability of the intestinal microbiota to metabolize the glycosylated isoflavones into more bioactive compounds, such as equol. Because Bifidobacterium pseudocatenulatum INIA P815 is able to efficiently deglycosylate daidzin into daidzein, the aim of this work was to confirm the influence of soy beverages fermented by B. pseudocatenulatum INIA P815 for enhancing equol production by fecal microbiota. Firstly, fecal samples from 17 participants were characterized in vitro, and we observed that 35.3% of them were able to produce equol from daidzein. In addition, the kinetics of equol production and degradation by fecal microbiota were evaluated, determining that 30-85% of equol is degraded after 24 h of incubation. Finally, the influence of fermented soy beverage on improving the production of equol by selected equol-producing fecal samples and by the equol-producing strain Slackia isoflavoniconvertens was analyzed through a colonic model. Fermented soy beverage enhanced the equol production from S. isoflavoniconvertens as well as the fecal samples whose microbiota showed high rates of equol degradation. The results obtained confirm that the fermentation of soy beverages with selected bacterial strains improves the functional properties of these beverages in terms of isoflavone metabolism and equol production.

Comparison of the five different definitions of equol producers: The relationship between blood and urine equol concentrations and blood parameters in 466 healthy men and women

BACKGROUND AND AIMS

No studies have compared various definitions of "equol producers" until now. Therefore, we aimed to explore the accuracy of five different definitions of equol producers (EQP) and their associations with health benefits.

METHODS

This is a cross-sectional study of 466 healthy Japanese men and women aged between 22 and 88 years. Equol producer proportions were calculated from their serum and urine isoflavone concentrations using five commonly used definitions. We then examined their accuracy, and associations with the blood parameters.

RESULTS

Proportions of equol ranged from 29 % in the most stringent definition to 47.6 % in the most sensitive definition. EQP identified under all definitions had significantly low serum PSA1 levels compared to nonequol producers (NEQP). The most stringent definition, which is defined as the urinary equol level of 1.0 μM and above, corresponded to the highest median serum equol level and was associated with better health outcomes. Male EQP identified by this definition seemed to have reduced risk of LDL2-hypercholesterolemia by 50 %, and female EQP identified by this definition seemed to have lower risk of high hs-CRP,3 compared to NEQP. Both the first and second stringent definition, which is defined as the serum equol level of 1.0 ng/mL and above, was associated with lower thyroid stimulating hormone level.

CONCLUSIONS

More stringent definitions were associated with better parameters in general. Combined with the dietary inquires, a reliable definition for equol producer is crucial to evaluate the health benefits of equol.

Mechanisms of gut bacterial metabolism of dietary polyphenols into bioactive compounds

The fruits and vegetables we consume as part of our diet are rich in bioactive metabolites that can prevent and ameliorate cardiometabolic diseases, cancers, and neurological conditions. Polyphenols are a major metabolite family that has been intensively investigated in this context. However, for these compounds to exert their optimal bioactivity, they rely on the enzymatic capacity of an individual's gut microbiota. Indeed, for most polyphenols, the human host is restricted to more basic metabolism such as deglycosylation and hepatic conjugation. In this review, we discuss the mechanisms by which gut bacteria metabolize the core scaffold of polyphenol substrates, and how their conversion into bioactive small molecules impacts host health.

A UPLC-MS/MS Based Rapid, Sensitive, and Non-Enzymatic Methodology for Quantitation of Dietary Isoflavones in Biological Fluids

Dietary isoflavones, a type of phytoestrogens, have gained importance owing to their health-promoting benefits. However, the beneficial effects of isoflavones are mediated by smaller metabolites produced with the help of gut bacteria that are known to metabolize these phytoestrogenic compounds into Daidzein and Genistein and biologically active molecules such as S-Equol. Identifying and measuring these phytoestrogens and their metabolites is an important step towards understanding the significance of diet and gut microbiota in human health and diseases. We have overcome the reported difficulties in quantitation of these isoflavones and developed a simplified, sensitive, non-enzymatic, and sulfatases-free extraction methodology. We have subsequently used this method to quantify these metabolites in the urine of mice using UPLC-MS/MS. The extraction and quantitation method was validated for precision, linearity, accuracy, recoveries, limit of detection (LOD), and limit of quantification (LOQ). Linear calibration curves for Daidzein, Genistein, and S-Equol were set up by performing linear regression analysis and checked using the correlation coefficient (r2 > 0.995). LOQs for Daidzein, Genistein, and S-Equol were 2, 4, and 2 ng/mL, respectively. This UPLC-MS/MS swift method is suitable for quantifying isoflavones and the microbial-derived metabolite S-Equol in mice urine and is particularly useful for large numbers of samples.

Equol and Resveratrol Improve Bone Turnover Biomarkers in Postmenopausal Women: A Clinical Trial

Estrogen deficiency is a major cause of loss of postmenopausal bone mineral density (BMD). This study aimed to evaluate the effects of equol and resveratrol on bone turnover biomarkers in postmenopausal women. Sixty healthy postmenopausal women were randomly assigned to receive 200 mg fermented soy containing 10 mg equol and 25 mg resveratrol or a placebo for 12 months. Whole-body BMD and bone turnover biomarkers, such as deoxypyridinoline (DPD), tartrate-resistant acid phosphatase 5b (TRACP-5b), osteocalcin, and bone-specific alkaline phosphatase (BAP), were measured at baseline and after 12 months of treatment. At the end of treatment, DPD, osteocalcin, and BAP significantly improved in the active group (p < 0.0001 for all) compared to the placebo group. Conversely, TRACP-5b levels were unaffected by supplementation (p = 0.051). Statistically significant changes in the concentrations of DPD (p < 0.0001), osteocalcin (p = 0.0001), and BAP (p < 0.0001) compared to baseline were also identified. Overall, the intervention significantly increased BMD measured in the whole body (p = 0.0220) compared with the placebo. These data indicate that the combination of equol and resveratrol may positively modulate bone turnover biomarkers and BMD, representing a potential approach to prevent age-related bone loss in postmenopausal women.

Advances in the Metabolic Mechanism and Functional Characteristics of Equol

Equol is the most potent soy isoflavone metabolite and is produced by specific intestinal microorganisms of mammals. It has promising application possibilities for preventing chronic diseases such as cardiovascular disease, breast cancer, and prostate cancer due to its high antioxidant activity and hormone-like activity. Thus, it is of great significance to systematically study the efficient preparation method of equol and its functional activity. This paper elaborates on the metabolic mechanism of equol in humans; focuses on the biological characteristics, synthesis methods, and the currently isolated equol-producing bacteria; and looks forward to its future development and application direction, aiming to provide guidance for the application and promotion of equol in the field of food and health products.

Soy isoflavone-specific biotransformation product S-equol in the colon: physiological functions, transformation mechanisms, and metabolic regulatory pathways

Epidemiological data suggest that regular intake of soy isoflavones may reduce the incidence of estrogen-dependent and aging-associated disorders. Equol is a metabolite of soy isoflavone (SI) produced by specific gut microbiota and has many beneficial effects on human health due to its higher biological activity compared to SI. However, only 1/3 to 1/2 of humans are able to produce equol in the body, which means that not many people can fully benefit from SI. This review summarizes the recent advances in equol research, focusing on the chemical properties, physiological functions, conversion mechanisms in vitro and vivo, and metabolic regulatory pathways affecting S-equol production. Advanced experimental designs and possible techniques in future research plan are also fully discussed. Furthermore, this review provides a fundamental basis for researchers in the field to understand individual differences in S-equol production, the efficiency of metabolic conversion of S-equol, and fermentation production of S-equol in vitro.

Potential Protective Mechanisms of S-equol, a Metabolite of Soy Isoflavone by the Gut Microbiome, on Cognitive Decline and Dementia

S-equol, a metabolite of soy isoflavone daidzein transformed by the gut microbiome, is the most biologically potent among all soy isoflavones and their metabolites. Soy isoflavones are phytoestrogens and exert their actions through estrogen receptor-β. Epidemiological studies in East Asia, where soy isoflavones are regularly consumed, show that dietary isoflavone intake is inversely associated with cognitive decline and dementia; however, randomized controlled trials of soy isoflavones in Western countries did not generally show their cognitive benefit. The discrepant results may be attributed to S-equol production capability; after consuming soy isoflavones, 40-70% of East Asians produce S-equol, whereas 20-30% of Westerners do. Recent observational and clinical studies in Japan show that S-equol but not soy isoflavones is inversely associated with multiple vascular pathologies, contributing to cognitive impairment and dementia, including arterial stiffness and white matter lesion volume. S-equol has better permeability to the blood-brain barrier than soy isoflavones, although their affinity to estrogen receptor-β is similar. S-equol is also the most potent antioxidant among all known soy isoflavones. Although S-equol is available as a dietary supplement, no long-term trials in humans have examined the effect of S-equol supplementation on arterial stiffness, cerebrovascular disease, cognitive decline, or dementia.

From Pre- and Probiotics to Post-Biotics: A Narrative Review

BACKGROUND AND AIMS

gut microbiota (GM) is a complex ecosystem containing bacteria, viruses, fungi, and yeasts. It has several functions in the human body ranging from immunomodulation to metabolic. GM derangement is called dysbiosis and is involved in several host diseases. Pre-, probiotics, and symbiotics (PRE-PRO-SYMB) have been extensively developed and studied for GM re-modulation. Herein, we review the literature data regarding the new concept of postbiotics, starting from PRE-PRO-SYMB.

METHODS

we conducted a search on the main medical databases for original articles, reviews, meta-analyses, randomized clinical trials, and case series using the following keywords and acronyms and their associations: gut microbiota, prebiotics, probiotics, symbiotic, and postbiotics.

RESULTS

postbiotics account for PRO components and metabolic products able to beneficially affect host health and GM. The deeper the knowledge about them, the greater their possible uses: the prevention and treatment of atopic, respiratory tract, and inflammatory bowel diseases.

CONCLUSIONS

better knowledge about postbiotics can be useful for the prevention and treatment of several human body diseases, alone or as an add-on to PRE-PRO-SYMB.

Main drivers of (poly)phenol effects on human health: metabolite production and/or gut microbiota-associated metabotypes?

Despite the high human interindividual variability in response to (poly)phenol consumption, the cause-and-effect relationship between some dietary (poly)phenols (flavanols and olive oil phenolics) and health effects (endothelial function and prevention of LDL oxidation, respectively) has been well established. Most of the variables affecting this interindividual variability have been identified (food matrix, gut microbiota, single-nucleotide-polymorphisms, etc.). However, the final drivers for the health effects of (poly)phenol consumption have not been fully identified. At least partially, these drivers could be (i) the (poly)phenols ingested that exert their effect in the gastrointestinal tract, (ii) the bioavailable metabolites that exert their effects systemically and/or (iii) the gut microbial ecology associated with (poly)phenol metabolism (i.e., gut microbiota-associated metabotypes). However, statistical associations between health effects and the occurrence of circulating and/or excreted metabolites, as well as cross-sectional studies that correlate gut microbial ecologies and health, do not prove a causal role unequivocally. We provide a critical overview and perspective on the possible main drivers of the effects of (poly)phenols on human health and suggest possible actions to identify the putative actors responsible for the effects.

Potential Protective Effects of Equol (Soy Isoflavone Metabolite) on Coronary Heart Diseases-From Molecular Mechanisms to Studies in Humans

Equol, a soy isoflavone-derived metabolite of the gut microbiome, may be the key cardioprotective component of soy isoflavones. Systematic reviews have reported that soy isoflavones have no to very small effects on traditional cardiovascular disease risk factors. However, the potential mechanistic mode of action of equol on non-traditional cardiovascular risk factors has not been systematically reviewed. We searched the PubMed through to July 2021 by using terms for equol and each of the following markers: inflammation, oxidation, endothelial function, vasodilation, atherosclerosis, arterial stiffness, and coronary heart disease. Of the 231 records identified, 69 articles met the inclusion criteria and were summarized. Our review suggests that equol is more lipophilic, bioavailable, and generally more potent compared to soy isoflavones. Cell culture, animal, and human studies show that equol possesses antioxidative, anti-inflammatory, and vasodilatory properties and improves arterial stiffness and atherosclerosis. Many of these actions are mediated through the estrogen receptor β. Overall, equol may have a greater cardioprotective benefit than soy isoflavones. Clinical studies of equol are warranted because equol is available as a dietary supplement.

Application of Phytochemicals in Immune Disorders: Their Roles Beyond Antioxidants

We are witnessing increased global pressure on immune system function as a result of climate change, exposure to xenobiotics, poor quality diets, increased psycho-social stress, and exposure to new infectious agents. Understanding how various phytochemicals and their metabolic byproducts produced by the microbiome modulate immune-related signal transduction pathways has opened a new chapter in medical nutrition that moves far beyond that of generalized antioxidant effects. Not only is precision nutrition now possible, there is an urgent need for it.

Effects of an equol-containing supplement on advanced glycation end products, visceral fat and climacteric symptoms in postmenopausal women: A randomized controlled trial

INTRODUCTION

Equol, an isoflavone derivative whose chemical structure is similar to estrogen, is considered a potentially effective agent for relieving climacteric symptoms, for the prevention of lifestyle-related diseases, and for aging care in postmenopausal women. We investigated the effect of an equol-containing supplement on metabolism and aging and climacteric symptoms with respect to internally produced equol in postmenopausal women.

METHODS

A single-center, randomized controlled trial (registration number: UMIN000030975) on 57 postmenopausal Japanese women (mean age: 56±5.37 years) was conducted. Twenty-seven women received the equol supplement, while the remaining received control. Metabolic and aging-related biomarkers were compared before and after the 3-month intervention. Climacteric symptoms were assessed every month using a validated self-administered questionnaire in Japanese postmenopausal women.

RESULTS

Three months post-intervention, the treatment group showed significant improvement in climacteric symptoms compared to the control group (81% vs. 53%, respectively, p = 0.045). We did not observe any beneficial effect on metabolic and aging-related biomarkers in the intervention group. However, in certain populations, significant improvement in skin autofluorescence, which is a measurement of AGE skin products, and visceral fat area was observed, especially among equol producers.

CONCLUSION

Women receiving equol supplementation showed improved climacteric symptoms. This study offered a new hypothesis that there may be a synergy between supplemented equol and endogenously produced equol to improve skin aging and visceral fat in certain populations.

Soy and Frequent Dairy Consumption with Subsequent Equol Production Reveals Decreased Gut Health in a Cohort of Healthy Puerto Rican Women

The U.S. Hispanic female population has one of the highest breast cancer (BC) incidence and mortality rates, while BC is the leading cause of cancer death in Puerto Rican women. Certain foods may predispose to carcinogenesis. Our previous studies indicate that consuming combined soy isoflavones (genistein, daidzein, and glycitein) promotes tumor metastasis possibly through increased protein synthesis activated by equol, a secondary dietary metabolite. Equol is a bacterial metabolite produced in about 20-60% of the population that harbor and exhibit specific gut microbiota capable of producing it from daidzein. The aim of the current study was to investigate the prevalence of equol production in Puerto Rican women and identify the equol producing microbiota in this understudied population. Herein, we conducted a cross-sectional characterization of equol production in a clinically based sample of eighty healthy 25-50 year old Puerto Rican women. Urine samples were collected and evaluated by GCMS for the presence of soy isoflavones and metabolites to determine the ratio of equol producers to equol non-producers. Furthermore, fecal samples were collected for gut microbiota characterization on a subset of women using next generation sequencing (NGS). We report that 25% of the participants were classified as equol producers. Importantly, the gut microbiota from equol non-producers demonstrated a higher diversity. Our results suggest that healthy women with soy and high dairy consumption with subsequent equol production may result in gut dysbiosis by having reduced quantities (diversity) of healthy bacterial biomarkers, which might be associated to increased diseased outcomes (e.g., cancer, and other diseases).

Equol-producing status affects exercise training-induced improvement in arterial compliance in postmenopausal women

Central arterial compliance decreases drastically after menopause. Regular intake of soy isoflavone and aerobic exercise increase arterial compliance. The equol is a metabolite of isoflavone daidzein by gut microbiome. We determined whether the equol-producing status affects aerobic exercise-induced improvement in carotid arterial compliance. Forty-three postmenopausal women were assigned to two intervention groups: 1) exercise and isoflavone (Ex+Iso, n = 27 females) or 2) isoflavone interventions (Iso; n = 16 females). Participants of the Ex+Iso intervention group completed an 8-wk aerobic exercise training, and all participants were administered with oral isoflavone supplements during the interventions. The equol-producing status (equol producers or nonproducers) was determined from urine equol concentrations after a soy challenge. In the Ex+Iso intervention group, carotid arterial compliance increased in the equol producers (0.084 ± 0.030→0.117 ± 0.035 mm²/mmHg), but not in the nonproducers (0.089 ± 0.028→0.097 ± 0.026 mm²/mmHg) after the intervention (interaction effect; P < 0.05). The magnitude of increases in carotid arterial compliance was significantly greater in the equol producers than in the non-equol producers (P < 0.05). In the isoflavone intervention group, there were no changes in any parameters after the intervention irrespective of the equol status. These results suggest that equol-producing status is obligatory to aerobic exercise training-induced improvements in central arterial compliance in postmenopausal women.NEW & NOTEWORTHY Isoflavone intake and aerobic exercise increase central artery compliance. Equol, a metabolite of isoflavone daidzein by gut microbiome, has beneficial effects on vascular function. We demonstrated for the first time that the interaction of aerobic exercise and equol production status plays an essential role in improvements in central artery compliance in postmenopausal women. More specifically, the equol-producing status was obligatory to exercise training-induced improvements in central arterial compliance in postmenopausal women.

A Systematic Review of the Effects of Equol (Soy Metabolite) on Breast Cancer

Equol is a soy isoflavone metabolite that can be produced by intestinal bacteria. It is lipophilic and resembles natural oestrogens with an affinity to oestrogen receptors. This review is focused on how equol affects breast cancer, as evidenced by in vivo and in vitro studies. Equol is considered chemoprotective in specific endocrine-related pathologies, such as breast cancer, prostate cancer, cardiovascular diseases, and menopausal symptoms. In humans, not everyone can produce equol from gut metabolism. It is postulated that equol producers benefit more than non-equol producers for all the endocrine-related effects. Equol exists in two enantiomers of R-equol and S-equol. Earlier studies, however, did not specify which enantiomer was being used. This review considers equol's type and concentration variations, pathways affected, and its outcome in in vivo and in vitro studies.

Nutritional and health factors affecting the bioavailability of calcium: a narrative review

Calcium is responsible for the effectiveness of various processes, and its supply in the diet is necessary for the normal function of the human body. Apart from being an important component of the skeleton, calcium also helps maintain the structure of cell organelles and regulates intracellular and extracellular fluid homeostasis. This review presents the nutritional and health factors that affect the bioavailability of calcium. Physiological conditions and factors such as pregnancy, infancy, menopause, old age, hormones, growth factors associated with calcium metabolism, diseases limiting its absorption, and intestinal microbiota are distinguished among endogenous factors. Although the calcium supply in the body is genetically conditioned and specific to each person, its qualitative and quantitative composition can be modified by external factors. The exogenous factors include dietary modifications with particular nutrients and pharmacological treatment. Adequate calcium levels increase bone protection and prevent osteoporosis, a disease involving low mineral bone mass.

Insight into Polyphenol and Gut Microbiota Crosstalk: Are Their Metabolites the Key to Understand Protective Effects against Metabolic Disorders?

Lifestyle factors, especially diet and nutrition, are currently regarded as essential avenues to decrease modern-day cardiometabolic disorders (CMD), including obesity, metabolic syndrome, type 2 diabetes, and atherosclerosis. Many groups around the world attribute these trends, at least partially, to bioactive plant polyphenols given their anti-oxidant and anti-inflammatory actions. In fact, polyphenols can prevent or reverse the progression of disease processes through many distinct mechanisms. In particular, the crosstalk between polyphenols and gut microbiota, recently unveiled thanks to DNA-based tools and next generation sequencing, unravelled the central regulatory role of dietary polyphenols and their intestinal micro-ecology metabolites on the host energy metabolism and related illnesses. The objectives of this review are to: (1) provide an understanding of classification, structure, and bioavailability of dietary polyphenols; (2) underline their metabolism by gut microbiota; (3) highlight their prebiotic effects on microflora; (4) discuss the multifaceted roles of their metabolites in CMD while shedding light on the mechanisms of action; and (5) underscore their ability to initiate host epigenetic regulation. In sum, the review clearly documents whether dietary polyphenols and micro-ecology favorably interact to promote multiple physiological functions on human organism.

Postbiotics-A Step Beyond Pre- and Probiotics

As an imbalance in the intestinal microbiota can lead to the development of several diseases (e.g., type 1 diabetes, cancer, among others), the use of prebiotics, probiotics, and postbiotics to alter the gut microbiome has attracted recent interest. Postbiotics include any substance released by or produced through the metabolic activity of the microorganism, which exerts a beneficial effect on the host, directly or indirectly. As postbiotics do not contain live microorganisms, the risks associated with their intake are minimized. Here, we provided a critical review of postbiotics described in the literature, including their mechanisms of action, clinical characteristics, and potential therapeutic applications. We detailed the pleiotropic effects of postbiotics, including their immunomodulatory, anti-inflammatory, antioxidant, and anti-cancer properties. Although the use of postbiotics is an attractive strategy for altering the microbiome, further study into its efficacy and safety is warranted.

Where to Look into the Puzzle of Polyphenols and Health? The Postbiotics and Gut Microbiota Associated with Human Metabotypes

The full consensus on the role of dietary polyphenols as human-health-promoting compounds remains elusive. The two-way interaction between polyphenols and gut microbiota (GM) (i.e., modulation of GM by polyphenols and their catabolism by the GM) is determinant in polyphenols' effects. The identification of human metabotypes associated with a differential gut microbial metabolism of polyphenols has opened new research scenarios to explain the inter-individual variability upon polyphenols consumption. The metabotypes unequivocally identified so far are those involved in the metabolism of isoflavones (equol and(or) O-desmethylangolesin producers versus non-producers) and ellagic acid (urolithin metabotypes, including producers of only urolithin-A (UM-A), producers of urolithin-A, isourolithin-A, and urolithin-B (UM-B), and non-producers (UM-0)). In addition, the microbial metabolites (phenolic-derived postbiotics) such as equol, urolithins, valerolactones, enterolactone, and enterodiol, and 8-prenylnaringenin, among others, can exert differential health effects. The knowledge is updated and position is taken here on i) the two-way interaction between GM and polyphenols, ii) the evidence between phenolic-derived postbiotics and health, iii) the role of metabotypes as biomarkers of GM and the clustering of individuals depending on their metabotypes (metabotyping) to explain polyphenols' effects, and iv) the gut microbial metabolism of catecholamines to illustrate the intersection between personalized nutrition and precision medicine.

Equol: A Bacterial Metabolite from The Daidzein Isoflavone and Its Presumed Beneficial Health Effects

Epidemiological data suggest that regular intake of isoflavones from soy reduces the incidence of estrogen-dependent and aging-associated disorders, such as menopause symptoms in women, osteoporosis, cardiovascular diseases and cancer. Equol, produced from daidzein, is the isoflavone-derived metabolite with the greatest estrogenic and antioxidant activity. Consequently, equol has been endorsed as having many beneficial effects on human health. The conversion of daidzein into equol takes place in the intestine via the action of reductase enzymes belonging to incompletely characterized members of the gut microbiota. While all animal species analyzed so far produce equol, only between one third and one half of human subjects (depending on the community) are able to do so, ostensibly those that harbor equol-producing microbes. Conceivably, these subjects might be the only ones who can fully benefit from soy or isoflavone consumption. This review summarizes current knowledge on the microorganisms involved in, the genetic background to, and the biochemical pathways of, equol biosynthesis. It also outlines the results of recent clinical trials and meta-analyses on the effects of equol on different areas of human health and discusses briefly its presumptive mode of action.

Effect of S-equol and Soy Isoflavones on Heart and Brain

BACKGROUND

Observational studies in Asia show that dietary intake of soy isoflavones had a significant inverse association with coronary heart disease (CHD). A recent randomized controlled trial (RCT) of soy isoflavones on atherosclerosis in the US, however, failed to show their benefit. The discrepancy may be due to the much lower prevalence of S-equol producers in Westerners: Only 20-30% of Westerners produce S-equol in contrast to 50-70% in Asians. S-equol is a metabolite of dietary soy isoflavone daidzein by gut microbiome and possesses the most antiatherogenic properties among all isoflavones. Several short-duration RCTs documented that soy isoflavones improves arterial stiffness. Accumulating evidence shows that both atherosclerosis and arterial stiffness are positively associated with cognitive decline/dementia. Therefore, potentially, soy isoflavones, especially S-equol, are protective against cognitive decline/dementia.

METHODS/RESULTS

This narrative review of clinical and epidemiological studies provides an overview of the health benefits of soy isoflavones and introduces S-equol. Second, we review recent evidence on the association of soy isoflavones and S-equol with CHD, atherosclerosis, and arterial stiffness as well as the association of atherosclerosis and arterial stiffness with cognitive decline/ dementia. Third, we highlight recent studies that report the association of soy isoflavones and S-equol with cognitive decline/dementia. Lastly, we discuss the future directions of clinical and epidemiological research on the relationship of S-equol and CHD and dementia.

CONCLUSIONS

Evidence from observational studies and short-term RCTs suggests that S-equol is anti-atherogenic and improves arterial stiffness and may prevent CHD and cognitive impairment/ dementia. Well-designed long-term (≥ 2years) RCTs should be pursued.

Inverse association between soy food consumption, especially fermented soy products intake and soy isoflavone, and arterial stiffness in Japanese men

Studies on the associations between soy food consumption and arterial stiffness are rare. The aim of the present study was to evaluate their associations in Japanese men. A total of 652 eligible men, aged 35-69 years, who underwent the measurement of brachial-ankle pulse wave velocity (baPWV) as an index of arterial stiffness were evaluated in this cross-sectional study. Information on their lifestyle characteristics, including dietary behavior, was obtained from a structured self-administered questionnaire. The frequency of total soy products as well as fermented and non-fermented soy products intakes was calculated, and the amounts of soy protein and soy isoflavone intakes were also estimated; these were then divided into tertiles and their associations with baPWV values were evaluated using general linear models. Higher frequency of fermented soy products intake was associated with decreased baPWV after adjusting for the multivariable covariates (P value for trend was 0.002, in Model 3). This association did not alter after further adjustment with a biomarker of systemic inflammation (serum high-sensitivity C-reactive protein (hs-CRP)) (P value for trend was 0.001, in Model 4). Total soy isoflavone consumption was also inversely associated with baPWV even after adjusting for multivariable covariates including serum hs-CRP (P value for trend was 0.043, in Model 4); however total soy protein consumption was not. These results demonstrated that greater consumption of soy food, especially fermented soy products and soy isoflavone was associated with reduced arterial stiffness, independent of systemic inflammation, in Japanese men.