Phytoestrogens in human biomatrices including breast milk

The health effects of soy: A reference guide for health professionals

Soy is a hotly debated and widely discussed topic in the field of nutrition. However, health practitioners may be ill-equipped to counsel clients and patients about the use of soyfoods because of the enormous, and often contradictory, amount of research that has been published over the past 30 years. As interest in plant-based diets increases, there will be increased pressure for practitioners to gain a working knowledge of this area. The purpose of this review is to provide concise literature summaries (400-500 words) along with a short perspective on the current state of knowledge of a wide range of topics related to soy, from the cholesterol-lowering effects of soy protein to the impact of isoflavones on breast cancer risk. In addition to the literature summaries, general background information on soyfoods, soy protein, and isoflavones is provided. This analysis can serve as a tool for health professionals to be used when discussing soyfoods with their clients and patients.

Neither soyfoods nor isoflavones warrant classification as endocrine disruptors: a technical review of the observational and clinical data

Soybeans are a rich source of isoflavones, which are classified as phytoestrogens. Despite numerous proposed benefits, isoflavones are often classified as endocrine disruptors, based primarily on animal studies. However, there are ample human data regarding the health effects of isoflavones. We conducted a technical review, systematically searching Medline, EMBASE, and the Cochrane Library (from inception through January 2021). We included clinical studies, observational studies, and systematic reviews and meta-analyses (SRMA) that examined the relationship between soy and/or isoflavone intake and endocrine-related endpoints. 417 reports (229 observational studies, 157 clinical studies and 32 SRMAs) met our eligibility criteria. The available evidence indicates that isoflavone intake does not adversely affect thyroid function. Adverse effects are also not seen on breast or endometrial tissue or estrogen levels in women, or testosterone or estrogen levels, or sperm or semen parameters in men. Although menstrual cycle length may be slightly increased, ovulation is not prevented. Limited insight could be gained about possible impacts of in utero isoflavone exposure, but the existing data are reassuring. Adverse effects of isoflavone intake were not identified in children, but limited research has been conducted. After extensive review, the evidence does not support classifying isoflavones as endocrine disruptors.

Soy-based renoprotection

Chronic kidney disease (CKD) is a significant public health problem as risk factors such as advanced age, obesity, hypertension and diabetes rise in the global population. Currently there are no effective pharmacologic treatments for this disease. The role of diet is important for slowing the progression of CKD and managing symptoms in later stages of renal insufficiency. While low protein diets are generally recommended, maintaining adequate levels of intake is critical for health. There is an increasing appreciation that the source of protein may also be important. Soybean protein has been the most extensively studied plant-based protein in subjects with kidney disease and has demonstrated renal protective properties in a number of clinical studies. Soy protein consumption has been shown to slow the decline in estimated glomerular filtration rate and significantly improve proteinuria in diabetic and non-diabetic patients with nephropathy. Soy’s beneficial effects on renal function may also result from its impact on certain physiological risk factors for CKD such as dyslipidemia, hypertension and hyperglycemia. Soy intake is also associated with improvements in antioxidant status and systemic inflammation in early and late stage CKD patients. Studies conducted in animal models have helped to identify the underlying molecular mechanisms that may play a role in the positive effects of soy protein on renal parameters in polycystic kidney disease, metabolically-induced kidney dysfunction and age-associated progressive nephropathy. Despite the established relationship between soy and renoprotection, further studies are needed for a clear understanding of the role of the cellular and molecular target(s) of soy protein in maintaining renal function.

Absorption, distribution, metabolism, and excretion of isoflavonoids after soy intake

Soy is the major source of dietary exposure to isoflavonoids (IFLs). Accumulating evidence supports a role for soy and IFLs in the protection against many chronic diseases including cancer. After soy intake we found a biphasic IFL appearance pattern in plasma as well as in urine that we suggest to be due to IFL absorption in the small intestine (ca. 10%) during the first 2h after intake and IFL absorption in the large intestine (ca. 90%) 4-6 h after intake. While each IFL disappears from the circulation at different times excellent correlations between urinary and circulating IFL values were discovered and algorithms to convert urinary excretion values into circulating levels were established. We suggest the term 'apparent bioavailability' when using urinary data to describe IFL exposure. The IFL bioavailability was found to be influenced by gut bacteria, oral antibiotic treatment (OABX), and an individual's age and health status. While daidzein (DE) and genistein start to be absorbed minutes after intake, equol (EQ) appears in plasma only after a minimum of 8h following soy intake owing to the required transit time of DE to the colon where the conversion of DE to EQ takes place by intestinal microbiota. We have also shown that the apparent IFL bioavailability is higher in children than adults, higher in healthy versus non-healthy individuals, and decreased in children but increased in adults during OABX. Finally, we propose to use a urinary EQ/DE ratio of 0.018 with a DE threshold to identify EQ producers. With this cutoff definition we observed that EQ production is inconsistent over time in 5-30% of both premenopausal and postmenopausal women.

Application of HPLC coupled with ultraviolet-photodiode array detection for the analysis of phytoestrogens in biological samples

HPLC/PDA methodology was developed for phytoestrogen analysis in human blood, urine, and breast milk. Applications of this technique in four different observational studies showed that urinary excretion rates of isoflavonoids reflects soy consumption reliably. A case-control study in Shanghai showed a decrease in risk to develop breast cancer for women with high urinary isoflavone excretion. These findings support a potential breast cancer preventive effect achieved by soy consumption in populations that eat soy foods habitually.

Urinary phytoestrogen excretion and postmenopausal breast cancer risk: the multiethnic cohort study

The objective of this study was to examine the association of urinary phytoestrogens with the risk of postmenopausal breast cancer. Participants in the Multiethnic Cohort Study included 36,458 postmenopausal women who provided blood or urine specimens. A nested case-control study of breast cancer with biospecimens was created in which cases diagnosed after specimen collection were matched to two controls. Two hundred fifty-one women with breast cancer and 462 controls had urine available for analysis of urinary phytoestrogens. Odds ratios (OR) and 95% confidence intervals (CI) were obtained using conditional logistic regression. A nonmonotonic inverse trend (P = 0.04) in breast cancer risk was associated with increasing urinary excretion of genistein (OR 25th-75th percentile, 0.88; 95% CI, 0.78-0.99) and total isoflavones (OR 25th-75th percentile, 0.80; 95% CI, 0.65-0.99). A significant reduction in breast cancer risk in Japanese-American women was associated with the highest compared with the lowest quartile excretion of urinary daidzein (OR, 0.41; 95% CI, 0.19-0.89; P(trend), 0.005). The risk of breast cancer was reduced among White women with the highest compared with the lowest quartile excretion of equol (OR, 0.27; 95% CI, 0.08-0.95), although the trend in risk was not significant (P = 0.07). Our results provide some support to the hypothesis that a diet rich in isoflavones from soy products reduces the risk of postmenopausal breast cancer, particularly in populations with comparatively high excretion of phytoestrogens.

Apparent bioavailability of isoflavones after intake of liquid and solid soya foods

Isoflavone (IFL) intake may provide numerous health benefits, but IFL bioavailability differences among soya foods remains uncertain. Urinary IFL excretion (UIE) was shown to provide a reliable surrogate for systemic IFL exposure and therefore can be used as a measure of 'apparent bioavailability' (AB). We investigated the AB of IFL in fourteen healthy adults, consuming two liquid and two solid soya foods in a crossover designed study. Volunteers consumed the foods with a self-selected breakfast, which was kept identical for all four soya items (soya nuts, soya milk, soya protein bar and soya protein powder drink in water; average 23.7 mg IFL, 88-96 % glycosides, by HPLC analysis) and collected all urine up to 26 h. Liquid foods showed initially higher UIE values than solid foods, but this difference was considerably reduced or disappeared entirely after 24-26 h. Conclusive AB results were obtained only after 24-26 h; earlier collections were not reliable. At 26 h, adjusted UIE values for daidzein (DE) were 20 micromol in the milk and bar and 17 micromol for the nut and powder; urinary genistein excretion was the highest in the milk group (10 micromol) followed by the nut, bar (both 6 micromol) and powder groups (5 micromol); the UIE for glycitein was the highest for bars (4 micromol), followed by powder and nuts (3 micromol), and milk (2 micromol). DE makes the largest contribution to urinary total IFL. The AB of IFL was found to be variable depending on the analyte and soya food consumed.

Gastrointestinal absorption and metabolism of soy isoflavonoids in ileal-canulated swine

The relative contribution of the small intestine to absorption and microbial metabolism of ingested isoflavonoids (IFN) was investigated in swine with canulae in distal ilea to facilitate collection of chyme (canula open). Weaned swine were fed a single meal containing ground roasted soybean and corn with canulae open followed by a second test soy diet at 48 h with canulae closed to allow passage of chyme into the large intestine. All remaining feedings were soy-free (corn-casein diet). Ileal effluent and urine were collected for 16 and 48 h, respectively, and analyzed for IFN and microbial metabolites of IFN. IFN in ileal effluent were present entirely as aglycones. IFN equivalents excreted for 24 h after ingesting the soy diet were not significantly different when canulae were open or closed. Urinary IFN aglycone equivalents on day 2 were similar to those on day 1 when canulae remained closed, but less than 10% of that on day 1 when canulae were open for 16 h postfeeding. Urinary concentrations of dihydrodaidzein, dihydrogenistein, O-desmethylangolensin, and equol exceeded IFN aglycone equivalents. These findings suggest extensive preabsorptive conversion of IFN glucosides to aglycones in the small intestine and relatively efficient microbial metabolism of IFN in weaned swine.

Phytoestrogenic isoflavonoids in epidemiologic and clinical research

Isoflavones (IFLs) are natural products to which humans have been traditionally exposed predominantly through soy foods; more recently humans are also exposed to them through soy protein addition to processed foods or through supplements. They are structurally similar to steroidal estrogens and can exert estrogenic or antiestrogenic effects depending on their concentrations and on the tissue considered. These properties qualify IFLs to be classified as phytoestrogens and are believed to account for many of the biological effects observed for soy and/or IFL exposure including benefits for bone and heart health or prevention of menopausal symptoms and certain types of cancer. In order to evaluate the function of IFLs, alone or when exposure happens through soy intake, pharmacokinetics and bioavailability are critical issues to be considered in epidemiologic and clinical research. For this purpose precise, accurate, robust, fast, and affordable techniques for IFL analyses are required.

The key importance of soy isoflavone bioavailability to understanding health benefits

Research over the past two decades has provided significant epidemiological and other evidence for the health benefits of the consumption of soy-based foods. A large number of dietary intervention studies have examined the effects of soy isoflavones on risk factors for cardiovascular disease and hormone-dependent cancers. However, these report large variability in outcome measures, very limited reproducibility between studies, and in some cases, controversy between the results of clinical trials using dietary soy or soy protein and isoflavone supplementation. This highlights a major gap in our understanding of soy isoflavone uptake, metabolism, distribution, and overall bioavailability. There are many potential factors that may influence bioavailability and a better knowledge is necessary to rationalize the inconsistencies in the intervention and clinical studies. This review focuses attention on our current state of knowledge in this area and highlights the importance of metabolism of the parent soy isoflavones and the critical role of gut microbiota on the bioavailability of these compounds and their metabolites.

Isoflavonoid glucosides are deconjugated and absorbed in the small intestine of human subjects with ileostomies

BACKGROUND

Although soy isoflavonoids have a number of health-promoting benefits, information concerning the sites of their absorption and metabolism in humans remains limited. Isoflavonoid absorption from the gut requires deconjugation of glucosides to aglycones.

OBJECTIVE

The objective was to investigate the role of the small intestine in isoflavonoid absorption and metabolism in humans.

DESIGN

Human subjects with fully functional gastrointestinal tracts (n = 6) and ileostomy subjects (n = 6) were fed a single soy meal containing 64.8 mg isoflavonoid aglycone equivalents (95% as glucosides). Metabolism of isoflavonoids in the upper gastrointestinal tract was examined by analyzing ileal effluent from ileostomy subjects, and absorption was assessed indirectly by quantifying isoflavonoids and several metabolites in 24-h urine pools.

RESULTS

Chyme contained 36.7% of ingested isoflavonoid aglycone equivalents, primarily (95.8%) as aglycones. Qualitative profiles (x +/- SEM) of isoflavonoid excretion in urine (daidzein > glycitein > genistein) and the quantity of isoflavonoid equivalents were not significantly different between the control (18.4 +/- 2.2 mg) and ileostomy (13.5 +/- 3.2 mg) subjects. Dihydrodaidzein was present in the urine of all subjects, although the amount excreted by ileostomy subjects was less than that excreted by the control subjects. The percentage of producers and mean quantities of dihydrogenistein, equol, and O-desmethylangolensin in the urine of ileostomy subjects also were lower than those of control subjects.

CONCLUSIONS

Ileostomy subjects efficiently deglycosylate isoflavonoid glucosides in the small intestine and appear to absorb aglycones with an efficiency comparable with that of control subjects. However, the production of microbial metabolites of isoflavonoids is limited in ileostomy subjects.

Secoisolariciresinol and matairesinol of sea buckthorn (Hippophaë rhamnoides L.) berries of different subspecies and harvesting times

Sea buckthorn (Hippophaë rhamnoides) seeds, berries, and berry fractions are often used as sources of bioactive ingredients for health products. The aim of the present study was to analyze lignans in these fractions of sea buckthorn. Secoisolariciresinol and matairesinol in seeds, fruit pulp/peel, and whole berries of sea buckthorn of three subspecies were analyzed by isotope dilution gas chromatography-mass spectrometry. The total content of the two lignans secoisolariciresinol and matairesinol varied widely from 8 to 139 microg/100 g in fresh berries and from 51 to 319 microg/100 g in dry berries. The content of secoisolariciresinol varied in the range of 34-313 microg/100 g of dry mass in the fruit pulp/peel and 93-355 microg/100 g in dry seeds. The content of matairesinol fell within the range of 3-25 microg/100 g in dry pulp/peel and 1-13 microg/kg in dry seeds. Wild H. rhamnoides ssp. sinensis contained a significantly higher total level of secoisolariciresinol and matairesinol in dry seeds, dry berries, and fresh berries compared with wild ssp. rhamnoides (253 vs 135 microg/100 g, P < 0.01, in seeds; 224 vs 153 microg/100 g, P < 0.05, in dry berries; 71 vs 29 g/100 g, P < 0.01, in fresh berries) and the cultivar of ssp. mongolica (253 vs 112 microg/100 g in seeds, 71 vs 9 microg/100 g in fresh berries). Harvesting dates had a significant influence on the content of the two lignans in seeds, fruit pulp/peel, and whole berries. This is the first report of lignans in sea buckthorn.

Urinary phytoestrogen concentrations in the U.S. population (1999-2000)

We report population-based urinary concentrations of phytoestrogens stratified by age, sex, and composite racial/ethnic variables. We measured the isoflavones - genistein, daidzein, equol, and O-desmethylangolensin (O-DMA) - and the lignans - enterolactone and enterodiol - in approximately 2500 urine samples from individuals aged 6 years and older who participated in the National Health and Nutrition Examination Survey (NHANES) in 1999 and 2000. We detected all phytoestrogens in over 70% of the samples analyzed; enterolactone was detected in the highest concentrations, and daidzein was detected with the highest frequency. The geometric means for each phytoestrogen were as follows: genistein, 22.3 microg/g; daidzein, 68.6 microg/g; equol, 7.65 microg/g; O-DMA, 3.95 microg/g; enterolactone, 217 microg/g; and enterodiol, 24.3 microg/g creatinine. The 95th percentiles for each phytoestrogen were as follows: genistein, 380 microg/g; daidzein, 944 microg/g; equol, 50.3 microg/g; O-DMA, 217 microg/g; enterolactone, 2240 microg/g; and enterodiol, 240 microg/g creatinine. Multivariate analyses showed statistically significant differences among many of the demographic subgroups. Adolescents had higher concentrations of genistein and equol than adults. Non-Hispanic whites had higher concentrations of enterodiol and equol than Mexican Americans or non-Hispanic blacks. Non-Hispanic whites also had higher concentrations of enterolactone and O-DMA than Mexican Americans. Mexican Americans had higher concentrations of genistein than non-Hispanic blacks; however, the opposite was found for O-DMA. Determination of phytoestrogen exposure in the US population will help us to better understand phytoestrogen consumption in the US and will assist us in elucidating the potential role of phytoestrogens in protecting against cancer and heart disease.

Determinants for urinary and plasma isoflavones in humans after soy intake

Consumption of soy foods leads to a biphasic appearance pattern of isoflavones (IFLs) in blood and urine, with peaks appearing at 1-2 h and 4-8 h after intake, but its causes are not understood. IFLs were measured repeatedly from plasma and/or urine after intake of soy foods, IFL glucosides, or aglycons without or with a mildly or radically reduced gut flora as a result of oral antibiotic (AB) treatment, or this combined with mechanical bowel preparation (AB+MBP). The typical biphasic IFL pattern in blood and/or urine was observed when a soy protein drink without (control) or with AB treatment or when IFL glucosides or aglycons were consumed. Soy intake combined with AB+MBP or consumption of puerarin led to a shift of the second peak to much later times. The first peak was absent after puerarin intake. Total urinary IFL recovery was more than 50% lower in the first 24 h, but overall 61% higher after AB+MBP vs. the control. When the area under the curves for corresponding time intervals were compared, individual or total urinary IFL excretion rates were highly correlated with individual or total plasma IFL levels (r=0.85-0.91; P <0.001). At the same urinary excretion rate three times more genistein than daidzein remained in the circulation. We conclude that urinary IFL excretion rates reflect circulating IFL levels, with daidzein appearing less in blood and more in urine than genistein. The first and second IFL peaks are due to uptake in the small and large intestine, respectively. The latter is the major locus of uptake (90%) at usual dietary IFL doses (0.15-1.5 mmol/kg body weight). A reduced gut flora delayed IFL uptake but led overall to increased urinary recovery because of less bacterial degradation in the intestine.

Reproductive toxicity assessment of chronic dietary exposure to soy isoflavones in male rats

Epidemiologic and experimental data suggest that consumption of diets that are rich in isoflavones may decrease cancer risk in the breast, prostate, and other tissues. Isoflavones such as genistein and daidzein are structurally similar to endogenous estrogens, and demonstrate both estrogenic and weak anti-estrogenic activities; these activities may underlie the impaired fertility and reproductive tract disorders reported in animals exposed to high doses of isoflavones. To identify possible effects of isoflavones on male fertility, we evaluated reproductive parameters in Wistar-Unilever rats receiving dietary exposure to PTI G-2535, a characterized mixture of soy-derived isoflavones containing 45% genistein, 23% daidzein, and 4% glycitein. Beginning at 10 weeks of age, rats received chronic dietary exposure to the soy isoflavone mixture (200 or 2000 mg/kg diet) for a minimum of 12 months. Controls received unsupplemented chow diet only for the same period. Dietary exposure to isoflavones induced no gross toxicity or alterations in body weight gain. Absolute and relative weights of the testis and epididymis in groups receiving high or low doses of isoflavones were comparable to those of controls, and histopathologic evaluations demonstrated that testicular morphology was similar in all study groups. Isoflavone exposure had no significant effects on spermatid count, sperm production, or sperm morphology in any group. These data suggest that the reproductive system of adult male rats is relatively insensitive to isoflavone toxicity at dose levels that demonstrate significant activity in cancer chemoprevention, and that male reproductive function is unlikely to be affected by long-term administration of isoflavones for cancer prevention or other purposes. The results of this study conducted in adult male rats differ from the significant alterations in reproductive parameters that have been reported in female rats receiving prenatal or juvenile exposure to isoflavones.

Identification of phytoestrogens in bovine milk using liquid chromatography/electrospray tandem mass spectrometry

In an international context of promoting scientific research on food safety, the interest in molecules having potential hormonal disrupting effects is growing. While industrial endocrine disruptors (phthalates, alkylphenols, PCBs, etc.) have been studied for several years, natural compounds like phytoestrogens remain less investigated. Accordingly, a research project was initiated with its main objectives to develop efficient analytical methods for a wide range of phytoestrogens in various food matrices, and to evaluate their occurrence in food products. Electrospray ionization with tandem mass spectrometric (MS/MS) analysis of isoflavones (genistein, daidzein, equol, formononetin, biochanin A), lignans (enterolactone, enterodiol), and coumestans (coumestrol) was investigated. This study revealed the formation of a large number of fragment ions in both positive and negative modes, corresponding to specific cleavages of the hydroxyl, carbonyl, and/or methoxy groups, and to Retro-Diels-Alder reactions. An LC/ESI-MS/MS method was developed consistent with the 2002/657/EC European decision criteria. An extraction and clean-up method was developed for milk samples. The identification limit for the proposed method appears to be under 1 ng/mL. The developed methodology was applied to various milk samples, and the occurrence of isoflavones (particularly equol) was demonstrated in the concentration range 1-30 ng/mL. The efficiency of the proposed analytical method permitted evaluation of a new and promising approach to a global risk assessment of natural estrogenic active substances including phytoestrogens and their metabolites.

Pharmacokinetics of the glucuronide and sulfate conjugates of genistein and daidzein in men and women after consumption of a soy beverage

BACKGROUND

The soy isoflavones genistein and daidzein are found in blood and tissues as aglycones, glucuronides, and sulfates. Isoflavone conjugates may serve as sources of aglycones at specific target tissues and may have bioactivity. Yet, very little is known about the plasma pharmacokinetics of isoflavone conjugates after soy ingestion.

OBJECTIVE

The objective of this study was to determine the plasma pharmacokinetics of glucuronide and sulfate conjugates of genistein and daidzein in humans after the consumption of a drink made with soy-protein isolate.

DESIGN

Six men and 6 women ( +/- SD age: 40.8 +/- 3 y) consumed a soy-protein-isolate drink. The pharmacokinetics of isoflavone glucuronide and sulfate conjugates were studied with the use of beta-glucuronidase (EC 3.2.1.31) and sulfatase (EC 3.1.6.1) digestion and liquid chromatography-mass spectrometry.

RESULTS

Glucuronides of genistein and daidzein made up a significantly lower percentage (P < 0.05) of the total isoflavone concentration in plasma (48% and 33%, respectively) than in urine. The percentages of sulfates of genistein and daidzein in plasma (8% and 26%, respectively) were 2- to 6-fold those in urine (P < 0.05). Approximately 30% of the total genistein or daidzein was comprised of mixed conjugates (one glucuronide and one sulfate). For daidzein sulfate, genistein sulfate, daidzein glucuronide, and genistein glucuronide, the time to peak (t(max)) was 4.5, 4.5, 4.5, and 6.0 h, respectively, and the apparent half-life (t(1/2 lambdaz)) was 3.1, 5.7, 3.2, and 8.4 h, respectively.

CONCLUSIONS

These data suggest that there are significant differences in the pharmacokinetics of sulfate and glucuronide conjugates of isoflavones. This may have important implications for the meal frequency and maintenance of target tissue bioactivity required to elicit potential health benefits.

The therapeutic potential of phytoestrogens

Phytoestrogens, such as the soya isoflavones genistein and daidzein, are currently being extensively investigated through both molecular, preclinical and clinical studies to determine their potential health benefits. Phytoestrogens may protect against chronic diseases such as hormone-dependent cancer (e.g., breast and prostate cancer), cardiovascular disease and osteoporosis. Investigations of phytoestrogen metabolism and bioavailability are also of great relevance. Conversion by gut microflora of daizein to its isoflavan metabolite equol, which is a more potent oestrogen and anti-oxidant, occurs only in some individuals (about 35% of subjects tested are equol excretors). This has considerable implications for daidzein bioavailability and also for cancer risk. Oxidative damage has been implicated in the development of heart disease and cancer and soya phytoestrogens have been reported to decrease plasma F(2)-isoprostane concentrations (biomarker for in vivo lipid peroxidation) and increase low density lipoprotein oxidation resistance. This anti-oxidant action of phytoestrogens could potentially contribute to their therapeutic efficacy. The findings from the current ongoing studies are all likely to contribute to determining the potential use of phytoestrogens as therapeutic agents.