Isoflavone Levels Research Articles

The Apparent Absorptions of Isoflavone Glucosides and Aglucons Are Similar in Women and Are Increased by Rapid Gut Transit Time and Low Fecal Isoflavone Degradation

We hypothesized that there would be no difference in apparent absorption, as assessed by urinary excretion, between isoflavone sources rich in glucosides or aglucons and that subjects with rapid gut transit time (GTT) and low fecal isoflavone degradation phenotype would absorb more isoflavones. Women (n = 13) with a fecal daidzein degradation rate constant, D(k) > 0.30 h(-1) (high degraders) and GTT of 106 +/- 11 h and women (n = 12) with D(k) < 0.20 h(-1) (low degraders) and GTT of 71 +/- 12 h were randomly assigned to 3 treatments: soygerm (1.1 micromol/kg body weight, n = 5 high degraders, 4 low degraders), fermented soygerm (3.3 micromol/kg, n = 4 high and 4 low degraders) or Novasoy isoflavone extract (1.5 micromol/kg, n = 4 high and 4 low degraders) for 7 d. By HPLC analysis, 24-h urinary excretion of soygerm was greater than Novasoy (51 +/- 6 vs. 26 +/- 6% of ingested dose, P < 0.05). Women of the low daidzein degradation phenotype had greater urinary isoflavone excretion than did women of the high daidzein degradation phenotype (51.6 +/- 4.8 vs. 33.8 +/- 4.7%, P < 0.05, mean of d1 and 7). The plasma total isoflavone level (estimated as a percentage of the ingested amount, mean of d 1 and 7) differed between women who consumed fermented soygerm and soygerm 3 h after feeding (1.8 +/- 0.3 vs. 0.5 +/- 0.3%, P < 0.05). Urinary excretions of aglucons and glucosides did not differ. The study confirmed that rapid GTT and low fecal isoflavone degradation rate increased the apparent absorption of isoflavones.

Soy Isoflavone Intake Lowers Serum LDL Cholesterol: A Meta-Analysis of 8 Randomized Controlled Trials in Humans

Clinical trials have noted hypocholesterolemic effects of soy protein intake, but the components responsible are not known. This meta-analysis of 8 randomized controlled trials was conducted to more precisely evaluate the effects of isoflavones on blood LDL cholesterol concentration independently of soy protein level. PubMed was searched for English-language "randomized controlled trial" articles published from 1966 to 2003 that described the effects of soy protein isolate (SPI) intake with measured isoflavone levels on blood lipids in humans using the search terms "soy protein," "isoflavones," and "cholesterol." From 31 articles identified by the search, 8 articles (with 10 low vs. high isoflavone comparisons) were selected for the meta-analysis. Subjects in each comparison consumed similar dietary fat, cholesterol, and fiber; the reported body weight of subjects did not change significantly during treatment. Serum LDL cholesterol concentration in subjects who consumed SPI (mean 50 g/d) with high isoflavone content (mean intake 96 mg/d) decreased by 0.15 mmol/L (95% CI: 0.08 to 0.23 mmol/L; P < 0.0001) compared with those who consumed the same SPI level with low isoflavone content (mean intake 6 mg/d). Decreases in serum LDL cholesterol concentration in hypercholesterolemic and normocholesterolemic subjects were 0.18 mmol/L (95% CI: 0.01 to 0.35 mmol/L; P = 0.03) and 0.14 mmol/L (95% CI: 0.06, 0.23 mmol/L; P = 0.0008), respectively. With identical soy protein intake, high isoflavone intake led to significantly greater decreases in serum LDL cholesterol than low isoflavone intake, demonstrating that isoflavones have LDL cholesterol-lowering effects independent of soy protein.

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.

Breast and uterine effects of soy isoflavones and conjugated equine estrogens in postmenopausal female monkeys.

In this study we evaluated the long-term effects of soy isoflavones on intermediate markers of cancer risk in the normal postmenopausal monkey breast and uterus. Ovariectomized female cynomolgus monkeys were randomized to receive one of three diets for 36 months: 1) isoflavone-depleted soy protein isolate (SPI-) (n = 57); 2) soy protein isolate with the equivalent of 129 mg/d isoflavones (SPI+) (n = 60); or 3) isoflavone-depleted soy protein isolate with conjugated equine estrogens at a dose scaled to approximate 0.625 mg/d in women (n = 62). End points included breast and uterine proliferation markers, sex steroid receptor expression, and serum estrogens. Epithelial proliferation and progesterone receptor expression in the breast and uterus were significantly higher in the conjugated equine estrogen group, compared with SPI+ and SPI- groups, whereas no significant differences were detected between the SPI+ and SPI- groups. SPI+ treatment resulted in significantly lower serum concentrations of estrone (P < 0.01) and estradiol (P < 0.05) vs. SPI-. Within the SPI+ group, serum isoflavone concentrations were inversely correlated with serum estrone and mammary glandular area. These findings suggest that high dietary levels of soy isoflavones do not stimulate breast or uterine proliferation in postmenopausal monkeys and may contribute to an estrogen profile associated with reduced breast cancer risk.

Increased serum and testicular androgen levels in F1 rats with lifetime exposure to soy isoflavones

The consequences of dietary soy isoflavones on serum and testicular androgen levels were examined in F1 male rats from a multigeneration study investigating the effects of diets varying in isoflavone content. Rats were fed either a soy-free casein based diet (AIN93G) or a diet in which alcohol-washed soy protein replaced casein as the protein source and to which increasing amounts of Novasoy, a commercially available isoflavone supplement were added. Analysis of these diets showed that the isoflavone content in each diet was 0 (diet 1; casein based control), 31.7 (diet 2; alcohol-washed soy-based diet control), 36.1 (diet 3), 74.5 (diet 4), 235.6 (diet 5) and 1046.6 (diet 6) mg total isoflavones/kg pelleted diet. The levels of isoflavones in diet 1 would represent a daily intake level of 0 mg isoflavones, diets 2 and 3 estimate a low soy-containing human diet (e.g. North American), diet 4 would correspond to Asian diets (e.g. Japanese) or adult humans taking isoflavone supplements, diet 5 approximates the isoflavone intake by babies fed soy based infant formula and diet 6 approximates fivefold the intake levels by babies or 10-fold the intake levels of adults consuming high isoflavone containing diets. Serum testosterone (T) from F1 male rats sacrificed on postnatal days (PND) 28, 70, 120, 240 and 360 were low at PND 28 (0.4 ng/ml), increased approximately five to sixfold at PND 70 (2.5–3.0 ng/ml) and thereafter declined to a steady state level of ∼1 ng/ml by PND 120. However, rats on diets 5 and 6 demonstrated altered serum testosterone profiles such that at days 120, testosterone levels remained significantly elevated at ∼3 ng/ml ( P<0.05). Serum dihydrotestosterone levels exhibited similar profiles and the levels in PND 120 rats on diet 5 or 6 were also significantly elevated (two to threefold, P<0.05). The intra-testicular testosterone concentration in rats on diet 5 was also elevated at PND 120 compared with diet 1 ( P<0.05). These findings show that F1 male rats continuously exposed to a mixture of dietary soy isoflavones from conception onwards exhibit altered serum and testicular androgen profiles.

Not All Soy Products Are Created Equal: Caution Needed in Interpretation of Research Results

Interest in the health benefits of soy foods has been intense among the research community, health professionals, and the public. At the same time, potential concerns associated with soy consumption, especially as related to soy isoflavones, have tempered the enthusiasm for making public health recommendations. On both accounts, the primary soybean isoflavone, genistein, has received the most attention. Because consumers are becoming increasingly confused by the often conflicting dietary messages, a balanced and accurate view of the risks and benefits of soy foods and soy food components is essential. Even among health professionals, confusion exists about proper nomenclature and about the precise composition of the agents under investigation. Levels of isoflavones are frequently assumed to be constant within categories of soy foods, and intakes are estimated rather than being directly analyzed. Furthermore, all too often research dealing singularly with genistein is interpreted by both health professionals and the media as equating directly with soy. Researchers often fail to fully understand the implications of their research outcomes and the context in which those outcomes should be placed. With the hundreds of publications yearly on soy and isoflavones, it is especially important to consider the literature in its entirety when making pronouncements about health effects. Efforts are needed by all to reduce the public confusion by adapting standardized approaches to the reporting of data. This paper provides a framework for both standardization of nomenclature and appropriate interpretation of data.

Biochemical Response of Soybean Roots to Fusarium solani f. sp. glycines Infection

The soil‐borne fungus Fusarium solani (Mart.) Sacc. f. sp. glycines (FSG) infects soybean [Glycine max (L.) Merr.] roots and causes the disease sudden death syndrome (SDS). The biochemical response of soybean roots to FSG infection, which has not been studied before, was investigated by comparing FSG‐inoculated and noninoculated roots of two partially resistant (‘PI 520733’ and ‘PI 567374’) and susceptible (‘Spencer’) genotypes. Activity of phenylalanine ammonia‐lyase (PAL), the first enzyme in the phenylpropanoid biosynthetic pathway, was increased in inoculated roots of all three genotypes. The phytoalexin glyceollin increased to much higher levels in inoculated roots of the partially resistant cultivars PI 520733 and PI 567374 than in the susceptible Spencer. The changes in phenolic metabolism were localized in lesion‐containing areas of roots rather than in the new portion growing under the FSG inoculum. No clear correlation was found between the glyceollin precursor daidzein (4′,7‐dihydroxyisoflavone) and its conjugates and glyceollin levels in root tissues; however, isoflavone levels increased only in roots of inoculated plants of partially resistant lines, even though constitutive isoflavone levels were higher in the susceptible control. The FSG growth on potato dextrose agar medium was inhibited by increasing concentrations of glyceollin. Induction of lignin synthesis was found in the inoculated roots of all three lines, with the highest rate of lignification observed in roots of the partially resistant genotypes, especially PI 567374. These studies show for the first time that FSG inoculation of soybean roots in soil induces the phenylpropanoid pathway to synthesize isoflavones, the phytoalexin glyceollin, and lignin, indicating that these compounds may be involved in the partial resistance response.

Limited Lipid-Lowering Effects of Regular Consumption of Whole Soybean Foods

Aim: To examine cardiovascular health benefits of foods containing a whole soybean extract. Methods: The study design was a randomized, placebo-controlled crossover trial of consuming soy-based milk and yoghurt (treatment) or equivalent dairy products (control) for 5 weeks each. Twenty-six mildly hypercholesterolaemic and/or hypertensive volunteers were recruited from the community as study volunteers, of which 23 completed. Main outcome measures included clinic and ambulatory blood pressure, arterial compliance, lipids, fatty acids and isoflavones in fasted blood and 24-hour urinary isoflavone excretion. Nutrient intakes were assessed initially and after each 5-week period. Multiple regression analyses were used to determine predictor variables in statistical models; order effects were tested by repeated measures ANOVA. Changes in Lp(a) were determined by Wilcoxon signed ranks tests; other differences between treatment and control were assessed by t tests. Results: Plasma and urinary isoflavones were markedly increased by whole soy supplementation but there were no overall differences in plasma lipids, blood pressure or arterial compliance between the soy and dairy diets. However, in 8 equol-positive subjects (equol detected in either plasma or urine), retrospective analysis revealed significant reductions in total cholesterol (8.5%), LDL cholesterol (10%), LDL:HDL ratio (13.5%), plasma triglycerides (21%) and lipoprotein(a) (11%) with the soy diet. These reductions were independent of changes in polyunsaturated fat and other macronutrient intakes. Conclusions: Regular consumption of whole soybean milk and yogurt products had no effect on plasma lipids, blood pressure or arterial compliance in at-risk subjects, despite substantially increasing isoflavone levels in blood and urine. Retrospective analysis suggests that improvement of plasma lipids may have been limited to equol-positive subjects.

Isoflavone Content of Kansas Soybeans

Isoflavones occurring in soybean seed have been thought to have a positive effect on the health of humans, especially in cancer prevention. This positive impact may be a result of their antioxidant properties, estrogenic activity, or a combination of mechanisms. The purpose of this study was to quantify and compare different levels of isoflavones in various Kansas soybean cultivars. Seeds of four different cultivars grown in 2001 at three different locations were analyzed. There were significant differences in total and individual amounts of isoflavones across both cultivars and locations. These results demonstrated a large variation in isoflavone content in different cultivars grown in different locations, suggesting that selection of cultivar and growing location are important parameters in optimizing the isoflavone content of soybeans grown in Kansas.

Phyto-œstrogènes du soja : problèmes posés chez le nourrisson allergique au lait de vache et consommant des formules à base de soja

This work presents isoflavones levels in soy-based infant formulas commercialised in France. These compounds are known to be both estrogenic and anti-gonadotrophic compounds. A comparison is made with soy based food supplements for estrogen deprived menopausal women. This work gives the latest scientific data on the effects of isoflavones in humans and presents the actual controversy on the effect of soy based infant formulas on human health. It gives the actual data on cow milk allergy in infants and explains what to do when cow milk allergy is suspected in infants. This paper warns paediatrics and advises them to avoid soy based infant formulas for infant below 6 months or to prefer formula with low isoflavone content if they are commercially available.

Effect of Isoflavones on Reproductive Performance, Testosterone Levels, Lipid Peroxidation, and Seminal Plasma Biochemistry of Male Rabbits

The objective of this study was to determine the effect of either 2.5 mg/kg Body Weight or 5 mg/kg Body Weight (BW) doses of isoflavones on semen quality, testosterone levels, lipid peroxidation and semen biochemistry of male New Zealand White rabbits. Animals were given both 2.5 mg/kg BW and 5 mg/kg BW doses of isoflavones. The tested doses were given to rabbits orally every other day for 13 weeks. Treatment with isoflavones caused an increase (p < 0.05) in libido (by decreasing the reaction time), sperm concentration, sperm motility (%), total motile sperm per ejaculate (TMS), packed sperm volume (PSV), total functional sperm fraction (TFSF), total sperm output, initial fructose concentration and normal sperm, while dead sperm was reduced compared to control animals. On the other hand, ejaculate volume, initial hydrogen ion concentration (pH) and plasma testosterone levels did not change in treated animals with both doses of isoflavones as compared to control. Concentrations of thiobarbituric acid-reactive substances (TBARS), total lipids, and low density lipoprotein were significantly (p < 0.05) reduced in seminal plasma of rabbits treated with either 2.5 mg/kg BW or 5 mg/kg BW doses of isoflavones. While, the activities of glutathione S-transferase (GST), lactate dehydrogenase (LDH), aspartate aminotransferase (AST), alanine aminotransferase (ALT), acid phosphatase (AcP), and alkaline phosphatase (AlP) were significantly (p < 0.05) increased in seminal plasma of treated animals. Also, total cholesterol, percentage cholesterol (out of total lipids), and high density lipoprotein were significantly (p < 0.05) increased, while triglyceride did not change in seminal plasma of treated animals. Supplementation at either level of isoflavones did not cause changes in live body weight (LBW), dry matter intake (DMI), and relative weights of testes and epididymis. The present results showed that either 2.5 mg/kg BW or 5 mg/kg BW doses of isoflavones caused an improvement of some semen characteristics and did not have negative effects on male fertility.

Enzyme-linked immunosorbent assay for the determination of isoflavones in alimentary important plants

The development of polyclonal antibody-based enzyme-linked immunosorbent assays (ELISA) for the determination of individual isoflavones, i.e. daidzein, genistein and biochanin and their homologues, is presented in this work. Isoflavone conjugates with bovine serum albumin were used as immunogens, coupled at the position C 7 and C 4’ via a carboxy methyl spacer. The developed ELISAs are highly specific, I&lt;sub&gt;50&lt;/sub&gt; values of the standard curves range between 0.3–1.2 ng/ml. The cross reactivities to other isoflavones are in acceptable range and the interference of non-isoflavonoid molecules is negligible. The immunoassays have been used for monitoring of changes in isoflavone levels in alimentary important plants, such as Medicago sativa, during germination; and during different vegetation stages of the Rutaceae family plants.

Biochemical Response of Soybean Roots to f. sp. Infection

The soil-borne fungus Fusarium solani (Mart.) Sacc. f. sp. glycines (FSG) infects soybean [Glycine max (L.) Merr.] roots and causes the disease sudden death syndrome (SDS). The biochemical response of soybean roots to FSG infection, which has not been studied before, was investigated by comparing FSG-inoculated and noninoculated roots of two partially resistant (‘PI 520733’ and ‘PI 567374’) and susceptible (‘Spencer’) genotypes. Activity of phenylalanine ammonia-lyase (PAL), the first enzyme in the phenylpropanoid biosynthetic pathway, was increased in inoculated roots of all three genotypes. The phytoalexin glyceollin increased to much higher levels in inoculated roots of the partially resistant cultivars PI 520733 and PI 567374 than in the susceptible Spencer. The changes in phenolic metabolism were localized in lesion-containing areas of roots rather than in the new portion growing under the FSG inoculum. No clear correlation was found between the glyceollin precursor daidzein (4′,7-dihydroxyisoflavone) and its conjugates and glyceollin levels in root tissues; however, isoflavone levels increased only in roots of inoculated plants of partially resistant lines, even though constitutive isoflavone levels were higher in the susceptible control. The FSG growth on potato dextrose agar medium was inhibited by increasing concentrations of glyceollin. Induction of lignin synthesis was found in the inoculated roots of all three lines, with the highest rate of lignification observed in roots of the partially resistant genotypes, especially PI 567374. These studies show for the first time that FSG inoculation of soybean roots in soil induces the phenylpropanoid pathway to synthesize isoflavones, the phytoalexin glyceollin, and lignin, indicating that these compounds may be involved in the partial resistance response.

Blood Isoflavone Levels during Intake of a Controlled Hospital Diet

Isoflavones are reported to have an estrogenic activity to prevent prostate cancer. Therefore, it is necessary to analyze the factors influencing the absorption and metabolism of isoflavones using detailed and precise dietary information. We evaluated the relationship between the amount of intake of soybean isoflavones in the diet and its serum levels in 88 hospitalized patients (22 with prostate cancer, 66 without cancer) with a mean age of 67.0+/-9.3 y. The intake amount of genistein and daidzein was significantly lower in the hospital diet than that in the ordinary daily diet. The serum levels of isoflavones were related to the amount of intake consumed during the day before blood collection (r=0.27 for genistein, r= 0.33 for daidzein), but not to the last meal before blood collection. While little relationship was observed between the amount of intake and serum levels of isoflavones in the equol producers, a marked relationship was noted in the non-producers (r=0.52 for genistein, r=0.67 for daidzein). Blood isoflavone levels decreased when the duration of the hospitalization was longer than 1 wk. These observations indicate that the serum isoflavone levels are correlated with the amount of intake of isoflavones during the preceding 2 wk and serve as an effective biomarker in individuals during the intake of the hospital diet. Further investigations, including the mechanism of the metabolism on isoflavones, are necessary for the evaluation of the preventive effect of isoflavones.

Phytoestrogen Intake and Endometrial Cancer Risk

Certain plant foods such as soybeans, whole grains, seeds, and dried fruit contain phytoestrogens that have anti-estrogenic properties that lower endogenous estrogen levels and can offer women some protection against the development of endometrial cancer. This study investigated the association of 3 forms of phytoestrogens (isofavones, coumestrol, and lignans) with the risk of endometrial cancer. Study subjects were 500 women with a diagnosis of endometrial cancer who were identified in and recruited from the Greater Bay Area Cancer Registry and the California Cancer Registry. They were black, Latina, and white women 35 to 79 years of age. A control group, matched for age and ethnicity to participants, consisted of 470 women found through random-digit dialing. Subjects in both groups were interviewed about dietary habits using a food-frequency questionnaire adapted from Block's Health History and Habits Questionnaire. On average, study subjects and control subjects had similar consumption of phytoestrogens, including all isoflavones, coumestrol, and the lignan matairesinol, but primary lignan secoisolariciresinol consumption was higher in study subjects than control subjects (P = .05). When compared by quartiles, women in the highest quartile of intake of isoflavones and lignans had a lower risk of endometrial cancer compared with those in the lowest quartile (odds ratio, 0.68 vs. 5.9, respectively). A comparison of different compounds adjusting for age, ethnicity, and total caloric intake found that consumption of the major isoflavones genistein and daidzein and the lignan seciosolariciresinol was associated with lower risk of endometrial cancer (P = .08, 0.02, and 0.001, respectively). Postmenopausal status strengthened these associations (P ≤.05 for isoflavones and 0.05≤ P ≥.08 for lignans). Obese women (body mass index greater than 32.23 m 2 ) who consumed the lowest levels of isoflavones or lignans had the greatest risk of endometrial cancer (odds ratio 6.9 for isoflavones and 4.7 for lignans).

Plasma isoflavone levels versus self-reported soy isoflavone levels in Asian-American women in Los Angeles County.

In a case-control study conducted among Asian-American women in Los Angeles County, we reported that the risk of breast cancer was significantly reduced in association with soy intake [Wu,A.H., Wan,P., Hankin,J. et al. (2002) Carcinogenesis, 23, 1491-1496]. In a subset of cases (n = 97) and controls (n = 97) we investigated the relationship between self-reported usual adult intake of soy isoflavones which was determined from a food frequency questionnaire and levels of plasma isoflavones (genistein and daidzein) and isoflavone metabolites (equol, dihydrogenistein and dihydrodaidzein) from a randomly timed blood specimen. In analyses conducted in cases and controls separately, levels of plasma genistein, daidzein and total isoflavones increased with increasing levels of self-reported intake of soy isoflavones. Breast cancer cases and control subjects did not differ in their respective associations between total plasma isoflavone levels and self-reported intake (P = 0.48). Among all subjects, there was a 3-fold difference in geometric mean plasma levels of total isoflavones [81.8 (95% CI = 53.4, 125.1) versus 26.4 nmol/l (95% CI = 16.6, 41.8)] between women in the highest quartile of soy isoflavone intake (>12.68 mg isoflavones/1000 kcal) compared with those in the lowest quartile of intake (<or=1.79 mg isoflavones/1000 kcal), a difference that was statistically significant (P = 0.002). The present study provides independent corroboration that breast cancer cases and control subjects can reliably recall their usual soy intake and that there is no evidence of selective recall biases between breast cancer cases and controls. These results further strengthen our previous observation of an inverse association between soy intake and breast cancer risk in the Los Angeles Asian Breast Cancer Study.

The OECD program to validate the rat uterotrophic bioassay. Phase 2: dietary phytoestrogen analyses.

Many commercial laboratory diets have detectable levels of isoflavones (e.g., phytoestrogens such as genistein [GN]) that have weak estrogenic activity both in vitro and in vivo. During validation studies of the uterotrophic bioassay, diet samples from 20 participating laboratories were collected and analyzed for three major phytoestrogens: GN, daidzein (DN), and coumestrol (CM). Soy phytoestrogens GN and DN were found at total phytoestrogen levels from 100 to 540 microg/g laboratory diet; a forage phytoestrogen, CM, ranged from nondetectable to 4 microg/g laboratory diet. The phytoestrogen levels were compared with both baseline uterine weights of the control groups and with the relative uterine weight increase of groups administered two weak estrogen agonists: bisphenol A (BPA) and nonylphenol (NP). The comparison uses a working assumption of additivity among the phytoestrogens, despite several significant qualifications to this assumption, to estimate total genistein equivalents (TGE). Some evidence was found that phytoestrogen levels in the diet > 325-350 microg/g TGE could diminish the responsiveness of the uterotrophic bioassay to weak agonists. This was especially true for the case of the intact, immature female version of the uterotrophic bioassay, where higher food consumption relative to body weight leads to higher intakes of dietary phytoestrogens versus ovariectomized adults. This dietary level is sufficient in the immature female to approach a biological lowest observable effect level for GN of 40-50 mg/kg/day. These same data, however, show that low to moderate levels of dietary phytoestrogens do not substantially affect the responsiveness of the assay with weak estrogen receptor agonists such as NP and BPA. Therefore, laboratories conducting the uterotrophic bioassay for either research or regulatory purposes may routinely use diets containing levels of phytoestrogens < 325-350 microg/g TGE without impairing the responsiveness of the bioassay.

Soy infant formula and phytoestrogens.

Soy infant formula contains high levels of the isoflavones, genistein and daidzein, which are commonly referred to as phytoestrogens. These are non-steroidal chemicals with structural similarities to estrogen. Infants consuming soy formula have high levels of circulating isoflavones. These are an order of magnitude greater than the levels of isoflavones which have been shown to produce physiological effects in adult women consuming a high soy diet. There is conflicting evidence about the risks and benefits of soy phytoestrogens, with research presenting a contradictory picture. Some reviewers suggest that early exposure to soy may prevent cancer and heart disease. However, there is very little research on the effects of consumption of soy phytoestrogens by human neonates. Against this generally positive view there is an increasing number of recent reports that suggest that in experimental animals, phytoestrogens have adverse effects with respect to carcinogenesis, reproductive function, immune function, and thyroid disease. Despite the absence of adequate scientific research that quantifies the level of risk to infants, most would argue for a precautionary approach to be taken in situations where there are potential developmental effects from the consumption of pharmacologically active compounds in infancy and childhood.

Metabolic engineering to increase isoflavone biosynthesis in soybean seed

Isoflavone levels in Glycine max (soybean) were increased via metabolic engineering of the complex phenylpropanoid biosynthetic pathway. Phenylpropanoid pathway genes were activated by expression of the maize C1 and R transcription factors in soybean seed, which decreased genistein and increased the daidzein levels with a small overall increase in total isoflavone levels. Cosuppression of flavanone 3-hydroxylase to block the anthocyanin branch of the pathway, in conjunction with C1/R expression, resulted in higher levels of isoflavones. The combination of transcription factor-driven gene activation and suppression of a competing pathway provided a successful means of enhancing accumulation of isoflavones in soybean seed.

Food sources of phyto-oestrogens and their precursors in Europe.

Phyto-oestrogens are dietary components found in some plants, which act in vivo like weak oestrogens. They may reduce the risk of some degenerative diseases moderated by oestrogen, including breast cancer and osteoporosis. The most widely studied are the isoflavones genistein and daidzein from soyabeans, but lignans may be more prevalent in the European diet. Soya foods have traditionally been consumed in the Orient for millennia, and are now widely available to European consumers. Levels of isoflavone in soyabeans from published literature vary between 560 and 3810 mg/kg, depending on variety and growing conditions. Soya protein concentrates and isolates derived from soyabeans contain 466-615 mg isoflavones/kg. Traditional soya milk, bean curds, bean sprouts, etc. contain 13 to 2030 mg isoflavone/kg, depending on the starting raw material and final water content. Fermented foods have a different isoflavone conjugate profile, which may be important in absorption and metabolism. Soya analogues of European foods include dairy and meat products, which contain 38 to 3000 mg total isoflavones/kg, depending the source of soya and dilution with other ingredients. A wide range of foods contain low levels of soya-derived isoflavones, but such foods do not make a significant contribution to mean intakes in Europe. Flaxseed is by far the richest source of lignan precursors. However, foods such as cereal brans, legumes and some vegetables are a more important source in the diets of Europeans because they are more widely consumed. For similar reasons, compared with soya isoflavones, lignans may be a more important source of phyto-oestrogens in the diets of Europeans.