大豆异黄酮微生物转化研究进展

大豆异黄酮是大豆在其生长过程中形成的一类次生代谢产物,具有抗氧化、抗癌、减少骨质流失、降低心脑血管发病率等多种生理功能。目前已知,被摄人机体的大豆异黄酮将被肠道微生物菌群转化为具有更高、更广生物学活性的不同产物。因此,大豆异黄酮对人体的有益调节作用强弱并不简单取决于摄人机体的净含量的多少,更在于被摄人机体的大豆异黄酮将如何被肠道菌群转化。本文从大豆异黄酮的组成与功能、大豆异黄酮体内吸收、代谢及微生物转化、转化产物的活性以及高效合成等方面进行了系统综述,对大豆异黄酮微生物生物转化研究现状和存在问题进行分析总结,并对今后发展趋势进行展望,旨在推动高活性大豆异黄酮微生物转化产物的研究与开发。     

The effects of soy isoflavones on obesity

Over the last decades, the prevalence of obesity and related diseases has increased rapidly in the Western world. Obesity is a disorder of energy balance and is associated with hyper-insulinemia, insulin resistance, and abnormalities in lipid metabolism, and it is one of the most important risk factors in the development of Type II diabetes, cardiovascular disease, atherosclerosis, and certain cancers. Because of the lower frequency of these diseases in Asian countries, attention has been turned toward the Asian diet, which consists highly of soy and soy-based products. The health benefits associated with soy consumption have been linked to the content of isoflavones, the main class of the phytoestrogens. As a result of their structural similarities to endogenous estrogens, isoflavones elicit weak estrogenic effects by competing with 17beta-estradiol (E2) for binding to the intranuclear estrogen receptors (ERs) and exert estrogenic or antiestrogenic effects in various tissues. The estrogenic activities of soy isoflavones are thought to play an important role in their health-enhancing properties. Additionally, the isoflavones have been proved to exert non-ER-mediated effects through numerous other pathways. Genistein, daidzein, and glycitein are the principal isoflavones in soy. Genistein is the most thoroughly examined of these, because it is the most prevalent isoflavone in soy and the most active of these compounds, because of its higher binding affinity for the ER. Genistein and daidzein can be obtained in high levels in humans under certain nutritional conditions, and epidemiologic and laboratory data suggest that these compounds could have health benefits in human obesity. This review will focus on the latest results of research on isoflavones and their effect on obesity in cell cultures, rodents, and humans.     

Inhibition of lipoxygenase by soy isoflavones: evidence of isoflavones as redox inhibitors

Hydroperoxides, the products of lipoxygenase mediated pathways, play a major role in the manifestation of chronic inflammatory diseases. Soy isoflavones act as antioxidants due to their ability to scavenge free radicals. Isoflavones inhibit the activity of soy lipoxygenase-1 and 5-lipoxygenase, from human polymorph nuclear lymphocyte in a concentration dependent manner. Spectroscopic and enzyme kinetic measurements have helped to understand the nature and mechanism of inhibition. Genistein is the most effective inhibitor of soy lipoxygenase 1 and 5-lipoxygenase with IC(50) values of 107 and 125 microM, respectively. Genistein and daidzein are noncompetitive inhibitors of soy lipoxygenase 1 with inhibition constants, K(i), of 60 and 80 microM, respectively. Electron paramagnetic resonance and spectroscopic studies confirm that isoflavones reduce active state iron to ferrous state and prevent the activation of the resting enzyme. A model for the inhibition of lipoxygenase by isoflavones is suggested.     

Dietary soy isoflavones inhibit activation of rat platelets

Isoflavones (isoflavonoids) have been proposed to be the active compounds that contribute to decreased mortality from chronic diseases in populations that consume large amounts of soy products. Diets containing soy protein with and without isoflavones were fed to rats to determine if these compounds could exert in vivo effects on physiologic markers of platelet activation. Three methods were employed to monitor platelet activation: measurement of electronic mean platelet volume, which is an indicator of shape change; monitoring of collagen-induced production of reactive oxygen signals (hydrogen peroxide); and determination of increases in phosphorylation of protein tyrosine residues after collagen stimulation. Apparent volumes were significantly smaller for platelets from rats fed isoflavones, suggesting that these platelets were in a more disc-like, quiescent state compared with platelets from rats fed the isoflavone-reduced diet (means +/- SEM, 5.37 +/- 0.08 vs. 5.70 +/- 0.06 fL, n = 6/group, P < 0.008). Results from the other functional tests were consistent with this finding. Platelet production of hydrogen peroxide was found be significantly lower 1, 3, and 5 minutes after addition of collagen for rats fed isoflavones versus rats fed the isoflavone-reduced diet (n = 6/group, P < 0.004). Phosphorylated tyrosine residues in platelet proteins after stimulation also were shown to be significantly lower in the platelets exposed to dietary isoflavones (n = 5/group, P < 0.047). These combined results indicate that soy isoflavones can alter early-event signaling networks that result in less activated platelets and may partially explain the beneficial effects of dietary soy against human heart disease.     

Role of soy isoflavones in the hypotriglyceridemic effect of soy protein in the rat

The present study was undertaken to determine whether isoflavones present in soy protein isolate contribute to the triglyceride-lowering effect of the protein relative to casein. Plasma triglyceride concentrations, their secretion rate into blood circulation, and post-heparin plasma lipoprotein lipase activity (a major determinant of intravascular catabolism of triglycerides) were measured in the fasted state in male Sprague-Dawley rats fed for 21 days one of three experimental diets varying in protein source (20% weight/weight): soy protein isolate, casein or casein to which 1.82 mg/g isoflavones (genistein and daidzein) were added to match the isoflavone content of soy protein isolate. Body weight gain was slightly lower in soy protein fed rats than in casein fed rats, but this effect was not statistically significant (P = 0.22). Casein plus isoflavones diet induced intermediary weight gain. A decrease in plasma total triglycerides was observed in rats fed soy protein and casein plus isoflavones compared with casein (P < 0.05), and there was a tendency to a positive correlation between weight gain and plasma triglyceride concentrations (r = 0.35, P = 0.06). However, no significant effect was observed on hepatic triglyceride concentrations, triglyceride secretion rate by the liver and post-heparin plasma lipoprotein lipase activity. These results show that soy protein isolate, in comparison with casein, has a hypotriglyceridemic effect in the rat and suggest that isoflavones may be responsible, at least in part, for this effect. The lowering effect of soy protein isolate and isoflavones on plasma triglyceride concentrations may be mediated by an alteration in energy balance, and possibly by the hepatic production of lipoproteins more susceptible to intravascular hydrolysis. Subtle but sustained changes in triglyceride secretion and post-heparin plasma lipoprotein lipase activity may also be implicated.     

Neutrophil myeloperoxidase chlorinates and nitrates soy isoflavones and enhances their antioxidant properties

Soy isoflavones and other polyphenolics have a number of potentially important beneficial effects on the pro-oxidant aspects of chronic inflammation. The impact of inflammatory cell-specific metabolism of polyphenolics, which can include halogenation and nitration, on the properties of these compounds has not been examined. Using either human neutrophils or differentiated human leukemia cells (HL-60) stimulated with phorbol ester to elicit a respiratory burst, the hypothesis that local generation of reactive oxygen and nitrogen species may metabolize and modify the biological properties of the soy isoflavones was examined. Coincubation of the stimulated cells with genistein or daidzein had no effect on the respiratory burst. Medium from stimulated cells in the presence of the isoflavones and NO(2)(-) increased the inhibition of copper-induced LDL oxidation. Mass spectrometry analysis of this medium revealed that monochlorinated, dichlorinated, and nitrated isoflavones, formed through a myeloperoxidase-dependent mechanism, were present. The consumption of genistein in the presence of cells was both extensive and rapid with > 95% of the genistein converted to either the chlorinated or nitrated metabolites within 30 min. Chemically synthesized 3'-chlorogenistein and 3'-chlorodaidzein increased the inhibition of LDL oxidation by approximately 4-fold and 2-fold over genistein and daidzein, respectively. These results lead to the hypothesis that inflammatory cell-specific metabolism of polyphenolics can modify the properties of these compounds at the local site of inflammation.     

Solvent extraction selection in the determination of isoflavones in soy foods

Acetonitrile is superior to acetone, ethanol and methanol in extracting the 12 phytoestrogenic soy isoflavone forms found in foods. At 53% organic solvent in water, raw soy flour, tofu, tempeh, textured vegetable protein and soy germ were evaluated for isoflavone extraction efficiency. The efficiency of acetonitrile extraction was demonstrated in mass balance evaluations of toasting of soy flour and soymilk heating.     

In-silico modeling studies of G-quadruplex with soy isoflavones having anticancerous activity

Telomere forms t-loop and G-quadruplex as the protective structure and the formation of these structures hinder the telomerase enzyme action. The binding affinities of ligand which stabilize the G-quadruplex represent good correlation with telomerase inhibition depicted in the anti-cancerous action. Most of the potent G-quadruplex stabilizing compounds suffer from the poor drug like properties. Herein, natural dietary compounds isoflavones were taken for the theoretical study to examine their stabilizing effect on G-quadruplex structure. The experimental G-quadruplex complexes were reproduced to obtain and validate the theoretical parameters. The obtained theoretical binding energies are in significant correlation with the experimental data. Analysis of binding shows isoflavones to be groove binders, and differential nature of quadruplex grooves might be beneficial in the selectivity aspects. Among all, derrubone was found to have better selectivity as well as affinity for the G-quadruplex comparable to well known ligand TMPyP4. The GBSA rescoring result enlightens the various interaction terms involved in the binding process. Cumulative stabilizing effects coming from VDW, ES, and GB energy terms attest to optimal binding of derrubone molecule which can be considered as a lead for the higher phases of drug designing. These findings are of great value in terms of unexplored groove binding modes and the studied natural compounds might be helpful to direct the focus of synthetic chemists in designing of new generation of antitumor agents.     

Enhanced bioavailability of soy isoflavones by complexation with beta-cyclodextrin in rats

In order to improve the solubility and bioavailability of a soy isoflavone extract (IFE), inclusion complexes (IFE-beta-CD) of the isoflavone extract with beta-cyclodextrin (beta-CD) were prepared and studied for their solubility and bioavailability. The aqueous solubility of the complexes of IFE with beta-CD (2.0 mg/ml) was about 26 times that of IFE itself (0.076 mg/ml). The same dosages of IFE and IFE-beta-CD were orally administered to SD rats (Sprague-Dawley) on an isoflavone glycoside (IFG) basis (daidzin, genistin and glycitin), and the plasma concentrations of daidzein, genistein and glycitein were measured over time to estimate the average AUC (area under the plasma concentration versus time curve) of the isoflavones. After the oral administration, the AUC values for daidzein, genistein and glycitein were 340, 11 and 28 microg x min/ml, respectively. In contrast, the respective AUC values after the administration of IFE-beta-CD were 430, 20 and 48 microg x min/ml. The bioavailability of daidzein in IFE-beta-CD was increased to 126% by the formation of inclusion complexes with beta-CD, compared with that in IFE. Furthermore, the bioavailability of genistein and glycitein in IFE-beta-CD formulation was significantly higher by up to 180% and 170%, respectively, compared with that of IFE p=0.008 and p=0.028, respectively). These results show that the absorption of IFE could be improved by the complexation of IFE with beta-CD (IFE-beta-CD).     

Influence of lifelong soy isoflavones consumption on bone mass in the rat

Soy isoflavones (IFs) have shown a bone-sparing effect through epidemiological studies in the Asian population. However, there is no evidence as to whether such protection would result from a lifelong exposure. We investigated the impact of an early exposure to IFs on bone status. Sixty female Wistar rats were fed either a standard diet (n=30) or the same food enriched with IFs (0.87 mg/g of diet) (n=30). After 1 month, they were allowed to mate, and were kept on the same regimen during the whole gestation and lactation periods. At weaning, female pups were each assigned to one of four nutritional groups; within each experimental group, animals were split into two groups, fed either the standard or the IF-rich diet. At 2, 3, 6, 12, 18, and 24 months after birth, 10 animals in each group were sacrificed. Femurs were collected for mechanical testing and bone mineral density (BMD) measurement. The rats perinatally or lifelong exposed to the IF-rich diet exhibited higher body weight and fat mass at 24 months of age. Peak bone mass was achieved between 6 and 12 months and did not differ between groups. In animals perinatally exposed to IF, BMD continued to increase. Thus, at 24 months, femoral total BMD (P<0.05), metaphyseal BMD (P<0.01), and failure load (P<0.05) were higher in the offspring born from mothers provided IF during pregnancy. Postnatal exposure alone did not improve bone parameters. This experiment provides evidence that perinatal exposure to phytoestrogens leads to a higher BMD later in life. It is suggested that these changes may have occurred as a consequence of programming effects, as has been shown for the endocrine and immune systems.     

Inactivation of thyroid peroxidase by soy isoflavones,in vitro and in vivo

Soy-containing foods and dietary supplements are widely consumed for putative health benefits (e.g. cancer chemoprevention, beneficial effects on serum lipids associated with cardiovascular health, reduction of osteoporosis, relief of menopausal symptoms). However, studies of soy isoflavones in experimental animals suggest possible adverse effects as well (e.g. enhancement of reproductive organ cancer, modulation of endocrine function, anti-thyroid effects). This paper reviews the evidence in humans and animals for anti-thyroid effects of soy and its principal isoflavones, genistein and daidzein.     

Multiple complexation of cyclodextrin with soy isoflavones present in an enriched fraction

In the present study we evaluated the complexation of daidzein/genistein/glycitein, present in an isoflavone enriched fraction (IEF), with β-cyclodextrin and 2-hydroxypropyl-β-cyclodextrin (HPβCD). Based on the increased solubility and higher complexation efficiency, IEF and HPβCD solid complexes were prepared by kneading, freeze-drying, co-evaporation, spray-drying and microwave. The solid complexes were characterized using Fourier transformed-infrared spectroscopy, differential scanning calorimetry, X-ray diffraction, scanning electron microscopy, and nuclear magnetic resonance spectroscopy, and the isoflavone content and solubility were determined by liquid chromatography. The results suggest that the isoflavones daidzein, genistein and glycitein may be externally associated to HPβCD as well as that isoflavones/HPβCD inclusion complexes are formed through the insertion of B-ring into the cyclodextrin cavity. Except for the freeze-dried IEF/HPβCD solid complex, all complexes showed similar content and solubility. In conclusion, the three isoflavones showed to be able to simultaneously complex with HPβCD.     

Molecular mechanisms of action of the soy isoflavones includes activation of promiscuous nuclear receptors. A review

Consumption of soy has been demonstrated to reduce circulating cholesterol levels, most notably reducing low-density lipoprotein (LDL) cholesterol levels in hypercholesterolemic individuals. The component or components that might be responsible for this effect is still a matter of debate or controversy among many researchers. Candidate agents include an activity of soy protein itself, bioactive peptides produced during the digestive process, or the soy isoflavones. Although soy intake may provide other health benefits including preventative or remediative effects on cancer, osteoporosis and symptoms of menopause, this review will focus on isoflavones as agents affecting lipid metabolism. Isoflavones were first discovered as a bioactive agent disrupting estrogen action in female sheep, thereby earning the often-used term 'phytoestrogens'. Subsequent work confirmed the ability of isoflavones to bind to estrogen receptors. Along with the cholesterol-lowering effect of soy intake, research that is more recent has pointed to a beneficial antidiabetic effect of soy intake, perhaps mediated by soy isoflavones. The two common categories of antidiabetic drugs acting on nuclear receptors known as peroxisome proliferator activated receptors (PPARs) are the fibrates and glitazones. We and others have recently asked the research question 'do the soy isoflavones have activities as either "phytofibrates" or "phytoglitazones"?' Such an activity should be able to be confirmed both in vivo and in vitro. In both the in vivo and in vitro cases, this action has indeed been confirmed. Further work suggests a possible action of isoflavones similar to the nonestrogenic ligands that bind the estrogen-related receptors (ERRs). Recently, these receptors have been demonstrated to contribute to lipolytic processes. Finally, evaluation of receptor activation studies suggests that thyroid receptor activation may provide additional clues explaining the metabolic action of isoflavones. The recent advances in the discovery and evaluation of the promiscuous nuclear receptors that bind many different chemical ligands should prove to help explain some of the biological effects of soy isoflavones and other phytochemicals.     

大豆异黄酮对大鼠乳腺癌细胞内cAMP/PKA信号途径的影响

本实验研究了大豆异黄酮对SHZ-88大鼠乳腺癌细胞内cAMP／PKA信号途径的影响。实验设3组：空白对照组、50μg／ml大豆黄酮及15μg／ml染料木素组。采用放射免疫测定法（RIA）检测了胞内cAMP的浓度、腺苷酸环化酶（adenylate cyclase,AC）和磷酸二酯酶（phosphodiesterase,PDE）的活性,用（γ-^32P）ATP掺入法测定cAMP依赖性PKA的活性,半定量RT-PCR法分析cAMP反应元件结合蛋白（cAMP response element binding protein,CREB）mRNA表达的变化。结果表明：在处理后5min,大豆黄酮组和染料木素组细胞的cAMP浓度分别比对照组升高了9．5％和11．0％（P〈0．05）：10min时,分别比对照组升高31．0％和40.3％（P〈0．01）。3组细胞的AC活性在处理时间内没有明显变化。但在处理后5min,大豆黄酮组和染料木素组细胞的PDE活性分别降至对照组的71．8％和71．6％（P〈0．05）。处理后20min,大豆黄酮组和染料木素组细胞PKA活性分别上升到对照组的125．8％和122．3％（P〈0．05）;到40min时仍维持在高水平。大豆黄酮组和染料木素组细胞CREB mRNA的表达量在处理后3h分别比对照组增加31．6％和51．1％（P〈0．05）;6h后开始下降。这些结果提示,大豆异黄酮能够激活大鼠乳腺癌细胞内cAMP／PKA信号途径;而且是通过抑制磷酸二酯酶的活性,导致胞内cAMP浓度升高而实现的。     

Effects of high-dose soy isoflavones and equol on reproductive tissues in female cynomolgus monkeys

Soy isoflavonoids have well-established estrogenic properties in cell culture and rodent models, raising concerns that high isoflavonoid intake may promote development of uterine and breast cancers. To address this concern we evaluated the effects of high-dose isoflavonoid supplements on reproductive tissues in a postmenopausal primate model. Thirty adult female ovariectomized monkeys (Macaca fascicularis) were randomized to receive a control diet 1) alone, 2) with 509 mg/day of the soy isoflavones genistein and daidzein (IF), or 3) with 1020 mg/day of racemic equol (EQ), an isoflavan, for approximately 1 mo. Doses are expressed in aglycone units as calorically scaled human equivalents. Total serum isoflavonoid levels 4 h postfeeding were <20 nmol/L, 2570.7 nmol/L, and 6944.8 nmol/L for control, IF, and EQ groups, respectively. Equol was the predominant serum isoflavonoid in both IF (72.5%) and EQ (99.7%) groups. Aglycones represented 0.9% (IF) and 0.5% (EQ) of total serum isoflavonoids. Histologically, uteri and mammary glands were diffusely atrophic in all groups. Uterine weight, endometrial thickness, glandular area, and epithelial proliferation in the uterus were not significantly different among treatment groups (ANOVA P > 0.1 for all). Endometrial progesterone receptor gene expression was significantly increased in the IF group (P = 0.02), while protein expression was not altered (ANOVA P > 0.1). Within the mammary gland, proliferation and indicators of estrogen exposure did not differ among treatment groups (ANOVA P > 0.1 for all). These findings indicate that high doses of dietary soy isoflavonoids have minimal uterotrophic or mammotrophic effects in an established primate model.     

Pharmacokinetics of isoflavones,daidzein and genistein,after ingestion of soy beverage compared with soy extract capsules in postmenopausal Thai women

Background  

Isoflavones from soybeans may provide some beneficial impacts on postmenopausal health. The purpose of this study was to compare the pharmacokinetics and bioavailability of plasma isoflavones (daidzein and genistein) after a single dose of orally administered soy beverage and soy extract capsules in postmenopausal Thai women.     

Revealing anti-inflammatory mechanisms of soy isoflavones by flow: modulation of leukocyte-endothelial cell interactions

The antiatherogenic effects of soy isoflavone consumption have been demonstrated in a variety of studies. However, the mechanisms involved remain poorly defined. Adhesion of monocytes to vascular endothelial cells is a key step within the inflammatory cascade that leads to atherogenesis. Many factors, including the physical forces associated with blood flow, regulate this process. Using an in vitro flow assay, we report that genistein, a principal component of most isoflavone preparations, inhibits monocyte adhesion to cytokine (TNF-alpha)-stimulated human vascular endothelial cells at physiologically relevant concentrations (0-1 microM). This effect is absolutely dependent on flow and is not observed under static conditions. Furthermore, this inhibition was dependent on activation of endothelial peroxisomal proliferator-activated receptor-gamma. No significant role for other reported properties of genistein, including antioxidant effects, inhibition of tyrosine kinases, or activation of estrogen receptors, was observed. Furthermore, the antiadhesive effects of genistein did not occur via modulation of the adhesion molecules E-selectin, ICAM-1, VCAM-1, or platelet-endothelial cell adhesion molecule-1. These data reveal a novel anti-inflammatory mechanism for isoflavones and identify the physical forces associated with blood flow and a critical mediator of this function.     

Protective actions of soy isoflavones and n-3 PUFAs on bone mass in ovariectomized rats

Ovariectomy (OVX) in female rats precipitates a marked reduction in endogenous estrogen concentrations and induces bone remodeling abnormalities that augment bone loss and increase the risk of developing osteopenia. This research examined the combined effects of two levels of soy isoflavones (IFs), trace (-IF) and high (+IF) (0.03 and 3.43 mg/g protein, respectively), and two levels of n-3 polyunsaturated fatty acids (PUFAs) on bone conservation in 2-month-old sexually mature OVX Sprague-Dawley rats. All dietary treatments provided 110.4 g/kg of fat from either safflower oil (N6) or a blend of safflower oil and menhaden oil (N3). OVX rats were randomly assigned to the N6-IF, N6+IF, N3-IF and N3+IF groups. The OVX and sham rats were euthanized after 12 weeks of feeding. Data for sequential femoral and tibial in vivo bone mineral density and bone mineral content (BMC) measurements were determined every 4 weeks. The hindlimb mineral data indicated a trend toward a positive bone mineral-sparing effect related to +IF. Among the OVX rats, those fed the N3+IF diet had a significantly higher value for tibial BMC. The concentration of serum pyridinoline cross-links was significantly lower in the N3+IF group. These findings indicate a complementary action of soy IFs and n-3 PUFAs for attenuating bone mineral reduction in OVX rats.     

Effect of circulating forms of soy isoflavones on the oxidation of low density lipoprotein

Soy isoflavones are thought to have a cardioprotective effect that is partly mediated by an inhibitory influence on the oxidation of low density lipoprotein (LDL). However, the aglycone forms investigated in many previous studies do not circulate in appreciable quantities because they are metabolised in the gut and liver. We investigated effects of various isoflavone metabolites, including for the first time the sulphated conjugates formed in the liver and the mucosa of the small intestine, on copper-induced LDL oxidation. The parent aglycones inhibited oxidation, although only 5% as well as quercetin. Metabolism increased or decreased their effectiveness. Equol inhibited 2.65-fold better than its parent compound daidzein and 8-hydroxydaidzein, not previously assessed, was 12.5-fold better than daidzein. However, monosulphated conjugates of genistein, daidzein and equol were much less effective and disulphates completely ineffective. Since almost all isoflavones circulate as conjugates, these data suggest that despite the increased potency produced by some metabolic changes, isoflavones may not be effective antioxidants in vivo unless they are deconjugated again.     

Growth performance,carcass characteristics and bioavailability of isoflavones in pigs fed soy bean based diets

A growth trial with 38 weaners (castrated male pigs) was designed to compare the growth performance and carcass quality of pigs fed diets containing either soy bean meal or soy protein concentrate in a pair-feeding design. Soy bean meal (SBM) and soy protein concentrate (SPC) differed in isoflavone (daidzein plus genistein) content (782?μg/g in SBM and 125?μg/g in SPC, respectively). During the experiment, all pigs were fed four-phases-diets characterized by decreasing protein concentrations with increasing age (weaner I, weaner II, grower, finisher diets). Rations of control and experimental groups were isoenergetic, isonitrogenous, and isoaminogen. The weanling pigs with an initial live weight of 8.4?±?1.1?kg were allotted to flat deck boxes. During the growing/finishing period (days 70?–?170 of age), the pigs were housed in single boxes. Both, the weaning and the grower/finishing performances (daily body weight gain, feed intake, feed conversion ratio) were similar in both groups. No differences were found between the groups in carcass composition (percentages of cuts, tissues, and protein/fat), and meat quality of pigs. Moreover, the IGF-1R mRNA expression in longissimus muscle was not influenced by the kind of soy product. However, circulating levels of isoflavones were clearly different between pigs fed SBM (genistein 239?±?44; daidzein 162?±?42; equol 12?±?4?ng/ml plasma) and animals fed SPC (genistein 22?±?9 and daidzein 8?±?3, and equol 10?±?3?ng/ml plasma). The results confirm the expected differences in the bioavailability of soy isoflavones, yet, there were no significant differences in performance of pigs fed either soy bean meal or soy protein concentrate.