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Soy Isoflavones

This is a work in progress and is being updated regularly. Check back regularly, as I will be steadily improving the site and adding more information.

Soy & Detoxification

Investigation Into Specific UGT1A1 Substrates

UGTA1A Substrates: flavanone, flavonoids (but not the flavonoid tangeretin, although it is the strongest inhibitor in one test), anthraflavic acid, soy isoflavone daidzein and its metabolites (though soy isoflavone genistein inhibits it).

REFERENCE: Wikipedia - Flavonoid

The term flavonoid refers to a class of plant secondary metabolites based around a phenylbenzopyrone structure. Flavonoids are most commonly known for their antioxidant activity. Flavonoids are also commonly referred to as bioflavonoids in the media – these terms are equivalent and interchangeable, since all flavonoids are biological in origin.

Flavonoids are widely distributed in plants fulfilling many functions including producing yellow or red/blue pigmentation in flowers and protection from attack by microbes and insects. The widespread distribution of flavonoids, their variety and their relatively low toxicity compared to other active plant compounds(for instance alkaloids) mean that many animals, including humans, ingest significant quantities in their diet.

Flavonoids have been referred to as "nature's biological response modifiers" because of strong experimental evidence of their ability to modify the body's reaction to allergens, viruses, and carcinogens. They show anti-allergic, anti-inflammatory, anti-microbial and anti-cancer activity. In addition, flavonoids act as powerful antioxidants, protecting against oxidative and free radical damage.

Good sources of flavonoids include all citrus fruits, berries, onions, parsley, legumes, green tea, red wine, seabuckthorn, and dark chocolate (that with a cocoa content of seventy percent or greater).

REFERENCE: Wikipedia - Isoflavone

Isoflavones are flavonoids acting as phytoestrogens that are thought of by many as useful in treating cancer.

Isoflavones are polyphenolic compounds produced almost exclusively by the members of the Leguminosae family (bean-family). They are long known for their estrogen-like effect on mammals. Views on isoflavones differ. Supporters toute studies which provide evidence of significant cholesterol reducing effects and protection against certain types of cancers, as well as other benefits. They are also very strong antioxidants. Critics of the inclusion of isoflavones in food claim that they increase the incidence of epithelial hyperplasia, which precedes cancerous tumors, and that they cause goitre and hyperthyroidism.

Isoflavones are produced from a branch of the general phenylpropanoid pathway that produces all flavonoid compounds in higher plants. Soybeans are the most common source of isoflavones and the major isoflavones in soybean are genistein and daidzein. The phenylpropanoid pathway begins from the amino acid phenylalanine, and an intermediate of the pathway, naringenin, is sequentially converted in to the isoflavone genistein by two legume-specific enzymes isoflavone synthase and a dehydratase. Similarly, another intermediate naringenin chalcone is converted to the isoflavone daidzein by sequential action of three legume-specific enzymes chalcone reductase, type II chalcone isomerase and isoflavone synthase. Plants use isoflavones and their derivatives as phytoalexin compounds to ward off disease causing pathogenic fungi and other microbes.

Most members of the Fabaceae family contain significant quantities of isoflavones. Analysis of levels in various species found that the highest levels of genistine and daidzein were found in psoralea (Psoralea corylifolia). Various legumes including kudzu (Pueraria lobata), lupine (Lupinus spp), fava bean (Vicia faba), and soy (Glycine max) contained substantial amounts of isoflavones according to this analysis. Highly processed foods made from legumes, such as tofu, retained most of their isoflavone content, with the exception of fermented miso, which actually had increased levels.

Other dietary sources of isoflavones include chick pea (biochanin A), alfalfa sprouts (formononetin and coumestrol) and peanuts (genistein)

Note: Yeargh! Peanuts are bad!

REFERENCE: Wikipedia - Genistein

Genistein is one of several known isoflavones. Isoflavones compounds, such as genistein and daidzein, are found in a number of plants, but soybeans and soy products like tofu and textured vegetable protein are the primary food source.

Genistein has estrogenic and antioxidant activities. It may also have anticarcinogenic, anti-atherogenic and anti-osteoporotic activities.

Genistein has weak estrogenic activity as measured in in vivo and in vitro assays. In vivo, its estrogenic activity is one-third that of glycitein and four times greater than that of daidzein.

Genistein/genistin intake has been associated with hypothyroidism in some.

SCIENCE: National Library of Medicine

Identification of human UDP-glucuronosyltransferase isoform(s) responsible for the glucuronidation of 2-(4-chlorophenyl)- 5-(2-furyl)-4-oxazoleacetic acid (TA-1801A).

We characterized the hepatic and intestinal UDP-glucuronosyltransferase (UGT) isoform(s) responsible for the glucuronidation of 2-(4-chlorophenyl)-5-(2-furyl)-4-oxazoleacetic acid (TA-1801A) in humans through several in vitro mechanistic studies. Assessment of a panel of recombinant UGT isoforms revealed the TA-1801A glucuronosyltransferase activity of UGT1A1, UGT1A3, UGT1A7, UGT1A9, and UGT2B7. Kinetic analyses of the TA-1801A glucuronidation by recombinant UGT1A1, UGT1A3, UGT1A9, and UGT2B7 showed that the K(m) value for UGT2B7 was apparently consistent with those in human liver and jejunum microsomes. The TA-1801A glucuronosyltransferase activity in human liver microsomes was inhibited by bilirubin (typical substrate for UGT1A1), propofol (typical substrate for UGT1A9), diclofenac (substrate for UGT1A9 and UGT2B7), and genistein (substrate for UGT1A1, UGT1A3, and UGT1A9). The inhibition by bilirubin, propofol, and diclofenac of the TA-1801A glucuronidation was less pronounced in jejunum microsomes than liver microsomes, suggesting that the contribution of UGT1A1, UGT1A9, and UGT2B7 to the TA-1801A glucuronidation is smaller in the intestine than the liver. In contrast, genistein strongly inhibited the TA-1801A glucuronosyltransferase activity in both human liver and jejunum microsomes. These results suggest that the glucuronidation of TA-1801A is mainly catalyzed by UGT1A1, UGT1A9, and UGT2B7 in the liver, and by UGT1A1, UGT1A3, and UGT2B7 in the intestine in humans.

In Short: Glucuronidation of TA-1801A is inhibited by bilirubin, propofol, diclofenac, and genistein. Genistein is a substrate for UGT1A1, UGT1A3, and UGT1A9. Genistein was the strongest inhibitor.


Both herbimycin-C and genistein are tyrosine kinase inhibitors.

REFERENCE: Wikipedia - Tyrosine Kinase

A tyrosine kinase (EC is an enzyme that can transfer a phosphate group to a tyrosine residue in a protein; these enzymes are a subgroup of the larger class of protein kinases. Phosphorylation is an important function in signal transduction to regulate enzyme activity. The hormones that act on tyrosine kinase receptors are generally growth hormones and factors that promote cell division (e.g., insulin, insulin-like growth factor 1, epidermal-derived growth factor).

In Short: I dont really know what this means. It might be important later, so I included it. Note the insulin connection, which may be important.

Isoflavones show tremendous potential to fight disease on several fronts. They have been shown to help prevent the buildup of arterial plaque, which reduces the risk of coronary heart disease and stroke. Isoflavones may help reduce breast cancer by blocking the cancer-causing effects of human estrogen. They may also prevent prostate cancer by hindering cell growth. Isoflavones can fight osteoporosis by stimulating bone formation and inhibiting bone resorption. They may even relieve some menopausal symptoms as well.

Soy isoflavones have antioxidant properties which protect the cardiovascular system from oxidation of LDL (the bad) cholesterol. Oxidized LDL cholesterol accumulates in the arteries as patches of fatty buildup which blocks the flow of blood, resulting in atherosclerosis. Genistein inhibits the growth of cells that form this artery clogging plaque. Arteries damaged by atherosclerosis usually form blood clots. This can lead to a heart attack if the clot goes to the heart, or a stroke if it goes to the brain.

Being a weak form of estrogen, isoflavones can compete at estrogen receptor sites, blocking the stronger version naturally produced by the body from exerting its full effect. Since high blood levels of estrogen are an established risk factor for breast cancer, weaker forms of estrogen may provide protection against this disease. Genistein has been found to hinder breast cancer as well as prostate cancer. Results from a new University of California study show that genistein slowed prostate cancer growth and caused prostate cancer cells to die. It acts against cancer cells in a way similar to many common cancer-treating drugs.

The highest amounts of isoflavones and soy protein are found in tempeh, whole soybeans (such as edamame), textured soy protein, soynuts, tofu and soy milk. Researchers recommend consuming at least one to two servings per day. A serving is equal to 1 ounce of soynuts; 4 ounces of tempeh, textured soy protein (cooked), or edamame; or 8 ounces of soymilk.

Genistein imitates, in some manner, estrogen (and other sexual hormones). It is thought that it “competes for estrogen receptors” and thus protects against the negative effects of estrogen. (Though there is some controversy about this) it does not seem to block the necessary functions of the sex hormones (though one paper speaks of a lengthening of the menstrual cycle, others argue this is a normalising and not a surpression). Genistein seems to be particularly helpful in all the “hormone responsive cancers”- breast, ovarian, uterine, prostate - and also with colon cancer.

Note: What happens when there is an overabundance of these helpful flavonoids in the body when they cant be processed out by the liver?

Sorafenib inhibits glucuronidation by the UGT1A1 (K ivalue: 1 µM) and UGT1A9 pathways (K ivalue: 2 µM). Systemic exposure to substrates of UGT1A1 and UGT1A9 may increase when co-administered with NEXAVAR.

In Short: Meaning that inhibitors of UGT1A1 (and any other enzyme) cause increased exposure to substrates of that enzyme, as expected.

The effects of the phytoestrogenic isoflavone genistein on the hepatic disposition of preformed and hepatically generated gemfibrozil 1-O-acyl glucuronide in the isolated perfused rat liver
Foods and complementary medicines contain phytoestrogenic isoflavones such as genistein, which undergo hepatic glucuronidation and excretion into bile and can potentially interfere with the hepatic elimination of other compounds. To investigate this potential, livers from Sprague-Dawley rats were perfused in single-pass mode with preformed gemfibrozil 1-O-acyl glucuronide (GG) (1 µM, n = 12) for 60 min followed by a 30-min washout phase, or with gemfibrozil (1 µM, n = 10) for 120 min. Half of each group of livers were co-perfused with genistein (10 µM) throughout the experiment. Perfusate and bile were analyzed for GG and gemfibrozil by HPLC. Co-perfusion with genistein significantly (P< 0.05) decreased the biliary extraction ratio of preformed GG from a mean of 0.82 to 0.65 and the first-order rate constant for transport of GG into bile from 0.054 ± 0.010 to 0.032 ± 0.008 min-1, but increased the first-order rate constant for sinusoidal efflux of GG from 0.128 ± 0.023 to 0.227 ± 0.078 min-1. Co-perfusion with genistein also significantly decreased the biliary extraction ratio of hepatically generated GG from 0.95 ± 0.01 to 0.83 ± 0.05. The findings confirm that genistein increases the potential for hepatic and systemic exposure to hepatically generated glucuronides, which may be important for patients on conventional drugs who consume isoflavones.

In Short: Genistein reduces the liver's ability to glucuronidate its substrates, therefore causing increased systemic exposure to them.

Modulation of liver canalicular transport processes by the tyrosine-kinase inhibitor genistein: Implications of genistein metabolism in the rat

Genistein affects transport in liver mainly through competition with other substrates at the sites of glucuronidation and transport via cmoat.

A number of studies already are under way or in the planning stages now. In one study, Barry Delclos, Ph.D., a researcher at FDA's National Center for Toxicological Research (NCTR), is overseeing a long-term, multigeneration study in rats of the soy component genistein. Early data using rats suggest that genistein alone may prompt undesirable effects such as the growth of breast tissue in males. The study will analyze the relationship between dosage and any adverse outcomes.

Sheehan also expresses concern about the effects soy may have on the function of the thyroid gland. Animal study results, some of which date back to 1959, link soy isoflavones to possible thyroid disorders, such as goiter. A 1997 study in Biochemical Pharmacology identified genistein and daidzein as inhibitors of thyroid peroxidase, which data suggest may prompt goiter and autoimmune disorders of the thyroid. Critics of these studies suggest that iodine deficiency may be a factor that needs to be considered when evaluating study results.

Tangeretin is one of the Citrus bioflavonoids. Tangeretin may play a role, like many flavonoids, in reducing the risk for certain cancers. Tangeretin has also shown promise in protecting nerve cells.

Note: Investigate what about soy may cause hypothyroidism. With decreased glucoronidation of isoflavones, they must circulate in the body a lot longer than usual, doing whatever they do to the thyroid a lot longer. Thus, Gilbert's relationship to hypothyroidism. Or at least one path to it.


Isoflavone Metabolism

Absorption and Metabolism of Isoflavones

Isoflavones represent one of the classes of the so-called "phytoestrogens." These bioactive non-nutrients are strikingly similar in chemical structure to estradiol, the main female hormone (1). Indeed, one can superimpose almost exactly the structures of estradiol and isoflavones so they become indistinguishable, and therefore they fit beautifully into the pocket representing the binding domain of the estrogen receptor. It is therefore not surprising that isoflavones share many of the properties of endogenous estrogens. Isoflavones have the ability to behave as estrogen mimics, but also have other important non-hormonal properties that have attracted the attention of many investigators.

The chemical form in which isoflavones occur is an important consideration since it can dramatically influence the biological activity, the bioavailability, and therefore the physiological effects of these dietary constituents. We showed almost two decades ago that intestinal microflora play a key role in the metabolism and bioavailability of phytoestrogens (2).

After ingestion, soybean isoflavones are hydrolyzed by intestinal glucosidases, which releases the aglycones: daidzein, genistein and glycitein. These may be absorbed or further metabolized to many specific metabolites, including equol and p-ethylphenol (3,4). The extent of this metabolism appears to be highly variable among individuals and is influenced by other components of the diet. A high carbohydrate milieu, which causes increased intestinal fermentation, results in more extensive biotransformation of phytoestrogens, with greatly increased formation of equol, a mammalian isoflavone metabolite.

This metabolic pathway may be clinically relevant to the efficacy of soybean isoflavones, because the estrogenic potency of equol is an order of magnitude higher than that of its plant precursor, daidzein. The importance of the microflora in the metabolic handling of isoflavones is well illustrated from observations that antibiotic administration blocks metabolism, germfree animals do not excrete the metabolites, and infants fed soy infant formulas in the first four months of life cannot form appreciable amounts of equol (5,6).

Like endogenous estrogens (7), isoflavones undergo an enterohepatic circulation; they are secreted in bile. This has been shown in rats (6,8,9), and our pharmacokinetic studies in humans (unpublished) indicate that absorption takes place along the entire length of the intestine, presumably by nonionic passive diffusion. There is no evidence, to my knowledge, that the glycoside conjugates can be absorbed, and this would be consistent with observations for flavonoids. Conjugation of isoflavones to glucuronic acid, a reaction catalyzed by one of the UDP-glucuronyltransferase isozymes, occurs on first-pass. Whether this takes place exclusively in the liver, or in the intestine is uncertain. Studies in rats suggest glucuronidation takes place during transport across the intestinal wall (6,9). Isoflavone glucuronide concentrations in portal venous blood of rats are high, and older studies of sheep showed that intestinal epithelia had a higher capacity for glucuronidation of equol than hepatocytes. Like estradiol, isoflavones are found in plasma mostly in the form of glucuronide conjugates, and to a lesser extent as sulfates (10); there also occur double conjugates.

Estrogens are strongly bound to the serum proteins, albumin and sex hormone binding globulin, so that <5 percent is circulating unbound, or free. The extent of protein binding is a major factor in governing the availability of estrogen for occupancy of nuclear receptor sites. Interestingly, phytoestrogens are less avidly bound to serum proteins; equol for example shows 10-fold less affinity for serum proteins that estradiol, and therefore a greater proportion will be available to occupy the estrogen receptor, which hypothetically may bolster the effectiveness of isoflavones.

We have determined the plasma half-life of daidzein and genistein, measured from their plasma appearance and disappearance curves to be 7.9 hours in adults; peak concentrations occur 6-8 hours after ingestion. Consequently, adherence to a soy-containing diet will ultimately lead to high steady-state plasma concentrations. Plasma concentrations of 50-800 ng/mL are achieved for daidzein, genistein and equol in adults consuming modest quantities of soy-foods containing in the region of 50 mg/day of total isoflavones. These values are similar to those of Japanese consuming their traditional diet (11).

In infants fed soy formulas plasma concentrations are even higher (5). Overall, when soy is consumed on a regular basis, levels far exceed normal plasma estradiol concentrations which in men and women generally range between 40-80 pg/mL. It was this early observation that led us to the hypothesis that with such disproportional levels one could anticipate hormonal effects from phytoestrogens (2).

Elimination of isoflavones from the body occurs via the kidneys. In urine, isoflavones are found mainly as glucuronide conjugates (3). Studies in animals and humans have indicated that the urinary output of isoflavones accounts for no more than 50 percent of the ingested dose, and since fecal excretion is minimal, there is currently an unaccounted balance. It is probable that this is explained by intestinal biotransformation to metabolites which are not presently being measured by investigators, and therefore it leads to questions regarding the reliability of using urinary isoflavone excretion as an indicator of dietary intake. p-Ethyl phenol, a metabolite formed by a cleavage of the isoflavone molecule, is not being quantified by most investigators. There is also a significant proportion of the population that lack the capacity to biotransform isoflavones (3), and a very high variability in quantitative excretion among individuals. Clinical efficacy of isoflavones is almost certainly related to the plasma circulating concentration and it is this endpoint that is likely to be the most reliable one to measure in clinical studies.

In summary, considerable knowledge of the metabolism and absorption of phytoestrogens was gained during the course of their discovery, however there are still gaps in our knowledge. The optimal dose of isoflavone required to have clinical effects remains to be established. In general we believe that 50 mg per day of aglycones is sufficient to have a clinical/biological effect. This would be consistent with intakes in countries consuming soy as a staple, and is the level at which demonstrable endocrine effects occur in premenopausal women (12). Dose response relationships remain to be established and factors governing their absorption and metabolism, which will govern efficacy will no doubt be understood in the near future.

In Short: Estradiol is the main female hormone. Isoflavones are phyroestrogens, and have a strikingly similar chemical structure. Intestinal microflora play a key role in the metabolism and bioavailability of phytoestrogens. After ingestion, soybean isoflavones are hydrolyzed by intestinal glucosidases, which releases the aglycones: daidzein, genistein and glycitein. These may be absorbed or further metabolized to many specific metabolites, including equol and p-ethylphenol (3,4). The extent of this metabolism appears to be highly variable among individuals and is influenced by other components of the diet. A high carbohydrate milieu, which causes increased intestinal fermentation, results in more extensive biotransformation of phytoestrogens, with greatly increased formation of equol, a mammalian isoflavone metabolite. The estrogenic potency of equol is an order of magnitude higher than that of its plant precursor, daidzein. Like endogenous estrogens, isoflavones undergo an enterohepatic circulation; they are secreted in bile. Glycoside conjugates cannot be absorbed. Conjugation of isoflavones to glucuronic acid, a reaction catalyzed by one of the UGT isozymes, most likely via the intestines. Like estradiol, isoflavones are found in plasma mostly in the form of glucuronide conjugates, and to a lesser extent as sulfates. Estrogens are strongly bound to the serum proteins, albumin and sex hormone binding globulin, so that <5 percent is circulating unbound, or free. The extent of protein binding is a major factor in governing the availability of estrogen for occupancy of nuclear receptor sites. Interestingly, phytoestrogens are less avidly bound to serum proteins; equol for example shows 10-fold less affinity for serum proteins that estradiol, and therefore a greater proportion will be available to occupy the estrogen receptor. Elimination of isoflavones from the body occurs via the kidneys. In urine, isoflavones are found mainly as glucuronide conjugates (3). Studies in animals and humans have indicated that the urinary output of isoflavones accounts for no more than 50 percent of the ingested dose, and since fecal excretion is minimal, there is currently an unaccounted balance. There is a significant proportion of the population that lack the capacity to biotransform isoflavones. Effectiveness of isoflavones is almost certainly related to the plasma circulating concentration.

REFERENCE: Wikipedia - Equol

Equol (4',7-isoflavandiol) is an isoflavandiol[1] metabolized from Daidzein, a type of Isoflavone, by bacterial flora in the intestines[2]. While endogenous estrogenic hormones such as estradiol are steroids, equol is a nonsteroidal estrogen. However, only about 30-50% of people have intestinal bacteria that make equol[3]. Equol may have beneficial effects on the incidence of prostate cancer[4] and physiological changes after menopause[5]. Other benefits may be realized in treating male pattern baldness, acne, and other problems because it functions as a DHT blocker[6]. S-Equol preferentially activates estrogen receptor type β[2][7]

Metabolism of isoflavones
Formation of aglycones

Isoflavones occur in foods in the form of glucosides which means that the isoflavones are bound to sugar (conjugated isoflavones). These glycosides are very water soluble. These conjugated isoflavones have to undergo further changes. When ingested, these conjugated isoflavones undergo hydrolysis by ß-glucosidases in the intestine, releasing the principal bioactive aglycones (daidzein, genistein and glycitein). These aglycones may be absorbed and further metabolized to many specific metabolites such as equol.

Influence of diet on isoflavones metabolism

Further metabolism of aglycones seems to be strongly influenced by the diet. A high carbohydrate environment, which causes increased intestinal fermentation, results in more phytoestrogens being transformed in equol. This may be relevant because the potency of equol is higher than that of its plant precursor, daidzein. Also, the intestinal microflora has an effect on the metabolism of isoflavones. When intestinal flora is low (antibiotics, germfree animals, newborn babies) metabolism falls down too. When the dietary intake of fat is high, intestinal microflora has difficulty in synthesizing equol from isoflavones.

Like endogenous estrogens (estradiol), isoflavones are metabolized in the intestines and liver. Absorption happens along the entire length of the intestine and they are secreted in bile and urine. Excretion of isoflavones metabolites can vary strongly between individuals. This may be influenced by the fact that each person has his own specific intestinal microflora population.

Once absorbed equol shows less affinity to be bound to serum proteins and therefore has a greater availability than estradiol. When soy is consumed on a regular basis (50 mg isoflavones/day), plasma isoflavone levels far exceed normal estradiol concentrations. This observation led to the hypothesis that isoflavone would be biologically active, conferring health benefits that could explain the relatively low incidence of hormone-dependent diseases in countries in which soy is a dietary staple.

In Short: Isoflavones occur in foods in the form of glucosides, meaning they are bound to sugar (conjugated). They are very water soluble. When ingested, they undergo hydrolysis by glucosidates in the intestine and release the principle bioactive aglycones (daidzein, genistein and glycitein). These aglycones may be absorbed and further metabolized to many specific metabolites such as equol. This further metabolism is strongly influenced by the diet. A high carb environment will cause more physoestrogens being transformed into equol, which is more potent that daidzien. Increased intake of fat works against this equol synthesis. Like estrogens, isoflavones are metabolized in the intestines and liver. Absorption happens along the length of the intesting and they are secreted in bile and urine. Excretion of isoflavone metabolites can vary strongly between individuals, possibly influenced by individual microflora populations. Once absorbed, equol binds less to serum proteins and is more available than estradiol. Regular soy ingestion creates a state where isoflavone levels far exceed normal estradiol concentrations.,X

Disposition of flavonoids via recycling: comparison of intestinal versus hepatic disposition.
The purpose of this study was to compare intestinal versus hepatic disposition of six flavonoids to fully characterize their first-pass metabolism. The perfused rat intestinal model and microsomes prepared from rat liver, duodenum, jejunum, ileum, and colon were used. The results indicated that isoflavone (12.5 microM) glucuronidation was highly variable among different microsomes prepared from liver or intestine. Comparing to liver metabolism, the intestinal metabolism had higher K(m) values (>2-fold). Likewise, the hepatic intrinsic clearance (IC, or a ratio of V(max)/K(m)) values of isoflavones were generally higher than their intestinal IC values (200-2000% higher), except for prunetin, for which the jejunal IC value was 50% higher than its hepatic IC. When comparing intestinal metabolism, the results showed that intestinal metabolism rates and V(max) values of isoflavones were less when an additional A-ring electron-donating group was absent (i.e., daidzein and formononetin). In the rat perfusion model using the whole small intestine, genistein (10 microM) was well absorbed (77% or 352 nmol/120 min). The first-pass metabolism of genistein was extensive, with 40% of absorbed genistein excreted as conjugated metabolites into the intestinal lumen. In contrast, the bile excretion of genistein conjugates was much less (6.4% of absorbed genistein). In conclusion, intestinal glucuronidation is slower in isoflavones without an additional A-ring substitution. Perfusion studies suggest that intestine is the main organ for genistein glucuronide formation and excretion in rats and may serve as its main first-pass metabolism organ.

In Short: Genistein is 77% absorbed in the small intestine. 40% of this absorbed genistein is excreted as conjugated metabolites into the intestinal lumen.Bile excretion of genistein conjugates was only 6.4% of absorbed genistein. Daidzein is glucuronidating more via the liver.

Plasma and urinary kinetics of the isoflavones daidzein and genistein after a single soy meal in humans
The aim of this study was to determine the pharmacokinetics and urinary excretion patterns of the soy isoflavones daidzein and genistein in humans. Six healthy men with a mean age of 37 y and a mean body mass index (in kg/m2) of 24 consumed a soybean flour-based meal on two occasions approximately 6 d apart. Blood samples and total urine were collected at intervals for the measurement of daidzein and genistein with HPLC. Isoflavone concentrations rose slowly and reached maximum values of 3.14 +/- 0.36 micromol/L at 7.42 +/- 0.74 h for daidzein and 4.09 +/- 0.94 micromol/L at 8.42 +/- 0.69 h for genistein. Elimination half-lives were 4.7 +/- 1.1 and 5.7 +/- 1.3 h for daidzein and genistein, respectively. The slow increase in plasma concentrations is consistent with the facilitation of absorption by hydrolysis in the small and large intestines of the glycosidic forms of the isoflavones present in soybean-containing foods to their corresponding aglycones. The rate of urinary excretion of daidzein was greater than that of genistein throughout the postmeal period, with mean recoveries of 62 +/- 6% and 22 +/- 4% (P < 0.001) for daidzein and genistein, respectively. However, the ratio of the areas under the plasma concentration versus time curves for genistein and daidzein was equal to the ratio of the concentrations of the respective isoflavones in the soy meal. It is concluded that the bioavailabilities of daidzein and genistein are similar, not withstanding the difference in urinary excretion.

In Short: Isoflavone concentrations reach their peak around 7-8 hours after ingestion. This slow absorption is due to intestinal hydrolysis. The glycosidic forms are transformed via hydrolysis into their corresponding aglycones. Bioavailabilities of diadzein and genistein are similar.

SCIENCE: National Library of Medicine

Analysis of soy isoflavone conjugation in vitro and in human blood using liquid chromatography-mass spectrometry.
Soybean products containing isoflavones are widely consumed in Western and Asian diets for putative health benefits, but adverse effects are also possible. The conjugated forms of isoflavones present in a soy nutritional supplement (predominately acetyl glucosides) and in blood from two human volunteers after consuming the supplement (7- and 4'-glucuronides and sulfates) were identified using liquid chromatography coupled with electrospray/tandem mass spectrometry. Circulating conjugates of genistein and daidzein were quantified using selective enzymatic hydrolysis and deuterated internal standards for liquid chromatography-electrospray/mass spectrometry. The levels of isoflavone glucuronides were much greater than the corresponding sulfates or aglycones. The substrate activities of genistein and daidzein were evaluated with recombinant human UDP glucuronosyl transferase (UGT) and sulfotransferase (SULT) by using enzyme kinetics. The SULTs 1A1*2, 1E, and 2A1 catalyzed formation of a single genistein sulfate; however, SULTs 1A2*1 and 1A3 had no observed activity. None of the SULTs showed activity with daidzein. Although several UGTs (1A1, 1A4, 1A6, 1A7, 1A9, and 1A10) catalyzed 7- and 4'-glucuronidation of genistein or daidzein, the UGT 1A10 isoform, which is found in human colon but not liver, was found to be specific for genistein. Glucuronidation of only genistein was observed in human colon microsomes, although nearly equal activity was observed for daidzein in human liver and kidney microsomes. These findings suggest a prominent role for glucuronidation of genistein in the intestine concomitant with absorption, although hepatic glucuronidation of absorbed genistein and daidzein aglycones is also likely.

In Short: Isoflavones are conjugated into 7-glucuronides, 4'-glucuronides, and sulfates. The levels of glucuronides were much greater than the corresponding sulfates of aglycones. SULTs 1A1*2, 1E, and 2A1 catalyzed formation of a single genistein sulfate, but had no effect on diadzein. Several UGTs (1A1, 1A4, 1A6, 1A7, 1A9, and 1A10) catalyzed 7- and 4'-glucuronidation of genistein or daidzein. The UGT1A10, which is in the colon but not the liver, was specific for genistein. Genestein glucuronidation takes place in both the intestine and the liver.

Long-Term Dietary Habits Affect Soy Isoflavone Metabolism and Accumulation in Prostatic Fluid in Caucasian Men
The soy isoflavones daidzein and genistein are believed to reduce prostate cancer risk in soy consumers. However, daidzein can be metabolized by the intestinal flora to form a variety of compounds with different bioactivities. In the current study, we investigated the influence of long-term dietary habits on daidzein metabolism in healthy Caucasian men (19–65 y old). A secondary goal was to compare plasma and prostatic fluid concentrations of 5 isoflavonoids: genistein, daidzein, equol, dihydrodaidzein, and O-desmethylangolensin. Baseline plasma levels of isoflavonoids were quantitated in 45 men by HPLC-electrospray ionization-MS. Participants then consumed a soy beverage daily for 1 wk, and post-soy isoflavonoid levels were quantitated in plasma and prostatic fluid. Equol was the only metabolite that appeared to be influenced by routine dietary habits. Stratified analyses revealed that men who had consumed 30 mg soy isoflavones/d for at least 2 y had 5.3-times the probability of producing equol than men who had consumed 5 mg/d (P = 0.014). Additionally, those men who consumed animal meat regularly had 4.7-times the probability of producing equol than men who did not consume meat. Last, the high concentrations of isoflavonoids in prostatic fluid increases the potential for these compounds to have direct effects in the prostate.

In Short: Equol is a metabolite of isoflavones. Men who consumed soy regularly for at least 2 years had 5.3x the probability of producing equol than those who had little or none. Men who consumed animal meat had 4.7x the probability of producing equol.

Health Effects of Gut Bacterial Metabolism of Daidzein
The indigenous microflora of the gastrointestinal tract have metabolic, trophic, and protective physiological functions within the human body. Metabolic functions include fermentation of nondigestible dietary ingredients and metabolism of endogenous mucous and dietary compounds.
Trophic functions include control of epithelial cell proliferation and differentiation. Protective functions include acting as a barrier against pathogens. Thus, individual differences in intestinal bacterial populations could potentially impact the health status and disease susceptibility of the host.

The relationship between phytoestrogen intake and human health are of interest in gut bacterial metabolism. These two fields intersect with investigation into the metabolism of the soy isoflavonoid daidzein. Daidzein is metabolized into equol and O-desmethylangolensin (O-DMA) by as yet unidentified intestinal bacteria. Evidence suggests that different bacteria are involved in these two pathways, and that there is considerable variation among individuals. In vitro and animal studies show that both of these metabolites are more biologically active than daidzein itself. Within the human population substantial differences in daidzein metabolism exist - 30-50% produce equol and 80-90% produce O-DMA. At the same time, observational and prospective studies indicate that protection against certain diseases, such as breast and prostate cancer, may be afforded by the ability to produce equol and O-DMA. This review explores the relationships (and potential mechanisms for these relationships) between human health and daidzein-metabolizing phenotypes.

In addition, research indicates that the equol- and O-DMA-producer phenotype is stable over time, suggesting that this ability may be under some degree of genetic control. These data leads to three hypotheses regarding the impact of isoflavones on human health; one, two or all three of these factors may be operating concurrently.

1) There may be four subpopulations among humans - equol producers and non-producers, and O-DMA producers and non-producers - each with a different physiological response to soy or isoflavone supplementation.
2) There is also evidence pointing to the ability to produce equol as a key factor, regardless of the amount of soy or daidzein consumed.
3) Genetic factors that are associated with, or responsible for, the equol-producer phenotype could have health consequences independent of soy or isoflavone consumption.

In Short: Daidzen is metabolised into equol and O-DMA by intestinal bacteria. Different bacteria produce each metabolite. These metabolites are more biologically active than the daidzen. 30-50% of people produce equol and 80-90% produce O-DMA.

In vitro Metabolism of Genistein and Tangeretin by Human and Murine Cytochrome P450s
Recombinant cytochrome P450 (CYP) 1A2, 3A4, 2C9 or 2D6 enzymes obtained from Escherichia coli and human liver microsomes samples were used to investigate the ability of human CYP enzymes to metabolize the two dietary flavonoids, genistein and tangeretin. Analysis of the metabolic profile from incubations with genistein and human liver microsomes revealed the production of five different metabolites, of which three were obtained in sufficient amounts to allow a more detailed elucidation of the structure. One of these metabolites was identified as orobol, the 3'-hydroxylated metabolite of genistein. The remaining two metabolites were also hydroxylated metabolites as evidenced by LC/MS. Orobol was the only metabolite formed after incubation with CYP1A2. Overall the presented observations suggest major involvement of CYP1A2 in the hepatic metabolism of these two flavonoids.

In Short: Genistein metabolites include Orobol, the 3'-hydroxylated metabolite, as well as two other hydroxylated metabolites. CYP1A2 has major involvement in the metabolism of genistein and tengeretin.

Soy Isoflavone Conjugation Differs in Fed and Food-Deprived Rats
An experiment clarifying the influence of food deprivation on the isoflavone conjugation pattern in rats was conducted. Food-deprived and fed rats were administered daidzein and genistein at 7.9 µmol/kg body, and changes in their plasma metabolites (i.e., free compounds, sulfates, glucuronides, sulfates/glucuronides) were measured quantitatively as a function of time. In the food-deprived group, total plasma daidzein and genistein reached maximum concentrations of 20.9 ± 4.4 and 11.4 ± 3.1 µmol/L, respectively, 10 min after administration, whereas in the fed group, the maxima were 2.4 ± 0.8 µmol/L for daidzein after 2 h and 1.8 ± 0.2 µmol/L for genistein after 4 h. In both groups, there were significantly more daidzein sulfates than genistein sulfates. Moreover, depriving rats of food before daidzein and genistein administration significantly increased plasma isoflavone sulfates with simultaneous significant decreases in plasma isoflavone glucuronides compared with fed rats. Additionally, nonconjugated daidzein and genistein appeared in plasma of food-deprived rats for 1 h after administration. Plasma concentrations of conjugates having both sulfate and glucuronide moieties were not significantly different between the groups.

In Short: Food-deprived rats fed daidzein and genistein had higher concentrations of these in their plasma than fed rats, as well as a higher ratio of sulfates to glucuronides.

Kinetics of Genistein and Its Conjugated Metabolites in Pregnant Sprague-Dawley Rats Following Single and Repeated Genistein Administration
Diets high in soy-based products are well known for their estrogenic activity. Genistein, the predominant phytoestrogen present in soy, is known to interact with estrogen receptors (ER) and ß and elicits reproductive effects in developing rodents. In the rat, genistein is metabolized predominantly to glucuronide and sulfate conjugates, neither of which is capable of activating ER. Therefore, it is critical to understand the delivery of free and conjugated genistein across the placenta to the fetus following maternal genistein exposure such that the potential fetal exposure to free genistein can be assessed... In maternal plasma, genistein glucuronide was the predominant metabolite.

In Short: Genistein is known to interact with estrogen receptors. In rats, genistein is metabolized predominantly to glucoronide and sulfate conjugates, neither of which is capable of activating estrogen receptors. Genistein glucuronide is the predominant metabolite.,1,7;journal,46,380;linkingpublicationresults,1:100462,1

A repeated 28-day oral dose toxicity study of genistein in rats, based on the 'Enhanced OECD Test Guideline 407' for screening endocrine-disrupting chemicals

We performed a 28-day repeated-dose toxicity study of genistein, which is known as a phytoestrogen.. Endocrine-disrupting effects of genistein were detected in females by histopathology. The changes included vacuolation and mucinification of the vaginal epithelium in the 400 and 1000 mg/kg groups; however, the incidences of the lesion were very low. Although increased serum prolactin levels were recorded in the males of the 1000 mg/kg group, we could not determine whether this was indeed induced by genistein. General toxicological effects of genistein were detected in blood chemistry, such as increased triglycerides and total protein and a decreased albumin/globulin ratio, as well as increased liver weight and glycogen deposition in the periportal hepatocytes.

Decreased ovarian hormones during a soya diet: implications for breast cancer prevention.

Soybeans contain a significant amount of the isoflavones daidzein and genistein, which are weak estrogens. The purpose of this study was to determine whether soya feeding decreases circulating levels of ovarian hormones and gonadotropins... Daily consumption of the soya diet reduced circulating levels of 17ß-estradiol by 25% (P < 0.01, Wilcoxon signed rank test, two-tailed) and of progesterone by 45% (P < 0.0001) compared with levels during the home diet period but had no effect on luteinizing hormone or follicle-stimulating hormone.. Mean daily serum levels of daidzein and genistein (free and conjugated forms) 15 h after soymilk were 2.89 ± 0.53 µg/ml and 0.85 ± 0.22 µg/ml, respectively, indicating systemic bioavailability of these substances.

Increased levels of estrogens in blood and urine correlate with increased risk for breast cancer (22, 23, 24).. Large cohort studies, one involving women in New York (27) and another the nationwide Nurse's Health Study (28) , found a positive association of serum estrogens and androgens and breast cancer development. 17ß-Estradiol stimulates breast and endometrium cell proliferation (21) . Progesterone antagonizes the proliferative effect of 17ß-estradiol on the endometrium. However, the fact that breast cell proliferation increases during the luteal phase of the menstrual cycle, when progesterone concentrations are the highest, suggests that progesterone may enhance breast cell proliferation (21 , 29).

The soya diet on average provided more energy from carbohydrate than did the home diets (50.1 versus 45.3% of calories; P = 0.02), less energy from protein (14 versus 17%; P = 0.01), and less fiber (6 versus 18.3%; P = 0.001; Table 1 ). There was individual variation in these dietary differences... The decrease in 17ß-estradiol was also inversely associated with change in protein intake, either with or without adjustment for age or urinary isoflavone levels. This suggests that a greater decrease in energy intake from protein during the soya diet may blunt the inhibitory effect of isoflavones on 17ß-estradiol levels.

During the soya diet period, the average serum cholesterol decreased by 6% (P = 0.07, paired t test), triglyceride by 17% (P = 0.08), HDL by 6% (P = 0.23), and LDL by 4% (P = 0.32). The ratios of cholesterol to HDL did not change significantly (not shown).

Isoflavones in soy exist mostly as glucosides (glycones), and the hydrolysis of these glycones to aglycones (free forms) by intestinal flora is thought to be necessary prior to systemic absorption (55) . The large interindividual variability in urinary recovery of ingested isoflavones is attributable possibly to interindividual differences in composition of intestinal flora as discussed previously (41) . Thus, plasma or urinary levels of isoflavones may be better biomarkers of soya exposure than isoflavone intake per se.

Dose-response relationships for genistein are frequently biphasic or U-shaped in many biological systems. For example, the effects of genistein on progesterone synthesis (50) , cell proliferation (56 , 57) , pituitary responsiveness to the stimulation of gonadotropin-releasing hormone (58) , and bone loss (59) can be stimulatory or inhibitory, depending upon genistein dose.


Soy & Hypothyroidism

My Summary:

Soybeans contain very high levels of phytic acids, which block the absorption of many minerals, including calcium and zinc. They also contain enzyme-inhibitors which block uptake of protein.
It contains many anti-thyroid agents which depress thyroid activity.

Researchers have identified isoflavones as potent anti-thyroid agents, and are capable of suppressing thyroid function, and causing or worsening hypothyroidism.

Note: It is possible for manufacturers to remove isoflavones from soy products, but it is not the practice.

Soy phytoestrogens disrupt endocrine function and have the potential to cause infertility and to promote breast cancer in adult women. They are potent antithyroid agents that cause hypothyroidism and may cause thyroid cancer. In infants, consumption of soy formula has been linked to autoimmune thyroid disease.
Free glutamic acid or MSG, a potent neurotoxin, is formed during soy food processing and additional amounts are added to many soy foods.
Soy foods contain high levels of aluminum which is toxic to the nervous system and the kidneys.

Soy isoflavones have been reported to reduce thyroid function in some people. A preliminary trial of soy supplementation among healthy Japanese, found that 30 grams (about one ounce) per day of soybeans for three months, led to a slight reduction in the hormone that stimulates the thyroid gland. Some participants complained of malaise, constipation, sleepiness, and even goiter. These symptoms resolved within a month of discontinuing soy supplements. However, a variety of soy products have been shown to either cause an increase in thyroid function or produce no change in thyroid function. The clinical importance of interactions between soy and thyroid function remains unclear. However, in infants with congenital hypothyroidism, soy formula must not be added, nor removed from the diet, without consultation with a physician, because ingestion of soy may interfere with the absorption of thyroid medication.

From Dr. Jacobon at Emory Endocrinology during a visit:

* vegetarian men have lower blood testosterone than omnivore men
* soybeans contain haemagglutinin, a clot-promoting substance that causes red blood cells to clump together. Also contains trypsin inhibitors

I was diagnosed and treated for hypothyroidism in my 20s. In my mid-40s, I decided to add soy to my diet to replace some of the meat and dairy in my diet. I read all the media hype and was sucked in, especially since I was on a high protein/low carb diet. Even my doctor encouraged it as she used soy every day. I had no idea that I had been poisoning my body for 3 years with something everyone, doctor included, suggested was healthy for me. It's in every health magazine, every talk show, every infomercial, web site, etc. Dr. Weil likes it, Julia Roberts likes it.

The upshot of it is that I have never been so ill with hypothyroid symptoms in my life, except at my initial diagnosis 20 years before. This was before I started browsing the internet for information about soy. In April 1999 I came across Mary Shomon's article at the Thyroid website about the dangers of soy for those with hypothyroidism and bells and whistles went off in my head! I had been literally poisoning myself for over 3 years with increased amounts of soy. I didn't even like the stuff yet I was consuming it to keep my protein intake high. By the way, I couldn't lose any more weight on the high protein/low carbo diet at all after adding the soy and I was following the diet strictly. Before adding the soy, I had lost 40 pounds on this diet and was hoping to lose the next 40 by the soy replacing meats and dairy. As soon as I stopped eating soy, my TSH, which had been creeping up to the top of the normal range (hypo), suddenly dropped into the hyper range. Just by eliminating the phytoestrogens and other components in soy, I have restored my health. The revelation about what soy can do to thyroid hormones shocked both my doctor and me!

I insisted on blood tests every 3 months as symptoms changed. I learned what tests to ask for and how to interpret them. I showed the doctor charts of symptoms. In my research I found that my gynecological problems were affecting my thyroid in a big way. Three months after having an cystic ovary removed, I went severly hyper (loss of estrogen) and it was at this point I had decided to add soy to my diet. What a mistake!

The symptoms I experienced were typically hypothyroid: exhaustion, severe muscle pain and cramping, sleep problems, physical sensitivites like skin that was sore to the touch, glare senstivity and aversion to loud noises. Exercise became almost impossible because of the sharp pains in my legs. My menstrual cycles became constant PMS and periods with severe cramping and pain. Most disturbing, my mental acuity was lost, I had mental confusion and decreased word retrieval. My hair was falling out, my skin dry and cracked, my fingernails and hair barely grew at all. I was often found lost somewhere in space while the world continued on without me. My digestive system was a mess and my body temperature was often below 97F. I was so cold at times I had to jump in a hot shower just to raise my body temperature to normal. Living like this can only be described as a fate worse than death at times. All this was due to soy consumption.

When I moved in with my vegan boyfriend, I began consuming huge amounts of soy --using silken tofu as a dairy substitute in vegan desserts and soups, as well as drinking soy milk, eating soy burgers, and stir-frying tofu. After we'd been living together about eight months, I began experiencing alternating diarrhea and constipation, abdominal pain, low energy, lowered libido, and general "brain fog."

After months of trying various colon cleansers and such, I discovered through a lengthy elimination diet that I had developed a soy intolerance. A visit to a gastroenterologist shed no light on this (he said he'd never heard of soy intolerance in adults) but he did discover that I had hypothyroidism. I have since been diagnosed with a multinodular goiter as well.

I believe the soy intolerance is directly related to my hypothyroidism and goiter; soy contains large amounts of goitrogens, a goiter producing chemical! I don't know which came first -- whether over consumption of soy kicked a latent thyroid problem into active mode, or whether my already hypothyroid body developed an intolerance to a food that was exacerbating its problems.

A combination of levothyroxine and cutting out all soy (including soy oil and soy lecithin, which is in most processed foods-- chocolate, bread, cereal, cookies, soup, ice cream etc and in most restaurant deep fryers) has returned me to health.

SCIENCE: National Library of Medicine

Actual levels of soy phytoestrogens in children correlate with thyroid laboratory parameters.

Thyroid hormones and thyroid autoantibodies, along with serum concentrations of two phytoestrogens of the isoflavone series, daidzein and genistein, were measured in 268 children without overt thyroid diseases, screened for iodine deficiency in one region of the Czech Republic. Since both phytoestrogens have been reported to inhibit thyroid hormone biosynthesis and in high concentrations to exert goitrogenic effects, we investigated whether their presence in the circulation could influence thyroid hormone function in a population where soy consumption is not common. Correlation analysis revealed a significant positive association of genistein with thyroglobulin autoantibodies and a negative correlation with thyroid volume. Multiple regression analysis of the relationships between actual phytoestrogen levels and measured thyroid parameters revealed only a weak but significant association between genistein and thyroid variables. Higher levels of free thyroxine were found in a subgroup of 36 children who ate soy food in the previous 24 h. In conclusion, only modest association was found between actual phytoestrogen levels and parameters of thyroid function. On the other hand, even small differences in soy phytoestrogen intake may influence thyroid function, which could be important when iodine intake is insufficient.

In Short: Daidzein and genistein have been reported to inhibit thyroid hormone biosynthesis and in high concentrations to exhibit goitrogenic effects. Genistein significantly raised thyroglobulin antibodies and lowered thyroid volume. Higher levels of free thyroxine were found in children who ate soy food in the previous 24 hours.

SCIENCE: National Library of Medicine

Genistein, a natural product from soy, is a potent inhibitor of transthyretin amyloidosis.

The misfolding of transthyretin (TTR), including rate-limiting tetramer dissociation and partial monomer denaturation, is sufficient for TTR misassembly into amyloid and other abnormal quaternary structures associated with three amyloid diseases: senile systemic amyloidosis, familial amyloid polyneuropathy, and familial amyloid cardiomyopathy. Small molecules can bind to one or both of the unoccupied TTR thyroid hormone-binding sites, stabilizing the native tetramer more than the dissociative transition state, thereby raising the kinetic barrier for tetramer dissociation. Herein we demonstrate that genistein, the major isoflavone natural product in soy, works in this fashion and is an excellent inhibitor of transthyretin tetramer dissociation and amyloidogenesis, reducing acid-mediated fibril formation to <10% of that exhibited by TTR alone. Genistein also inhibits the amyloidogenesis of the most common familial amyloid polyneuropathy and familial amyloid cardiomyopathy mutations in TTR: V30M and V122I, respectively. Genistein additionally inhibits tetramer dissociation under physiological conditions thought to lead to slow amyloidogenesis in humans. Furthermore, this natural product exhibits highly selective binding to TTR in plasma over all of the other plasma proteins. Isothermal titration calorimetry shows that genistein binds to TTR with negative cooperativity (K(d1) = 40 nM, K(d2) = 1.4 microM). The benefits of using a nutraceutical such as genistein to treat orphan diseases such as the TTR amyloidoses include known oral bioavailability and safety data. It is conceivable that some patients could benefit from simply increasing their intake of soy products or supplements.

In Short: Transthyretin transports T4. Genistein also binds to Transthyretin, and does so before all over plasma proteins. This study is in relation to a disease caused by transthyretin misassembly.

What Is Transthyretin?

REFERENCE: Wikipedia - Transthyretin

Transthyretin (TTR) is a serum and cerebrospinal fluid carrier of the thyroid hormone thyroxine (T4). It functions in concert with two other proteins, thyroxine-binding globulin (TBG) and albumin in a system where TBG possesses the highest affinity, yet lowest plasma concentration, TTR has a lower affinity, yet higher concentration, and albumin is the poorest binder, but has a much higher plasma concentration. TTR also acts as a carrier of retinol (vitamin A) through an association with retinol binding protein (RBP).

Numerous other small molecules are known to bind in the thyroxine binding sites, including many natural products (such as resveratrol), drugs (diflunisal, flufenamic acid), and toxins PCB. Since TTR binds promiscuously to many aromatic compounds, and generally does not bind T4 in serum, there is speculation that TTR's "true function" is to generally sweep up toxic and foreign compounds in the blood stream.

In Short: Transthyretin transports T4 but also binds to many other things, including Genistein, drugs, toxins, and aromatic compounds. Meaning, possibly, that its effectiveness in transporting T4 is reduced when Genistein and other toxin levels are high.

SCIENCE: National Library of Medicine

Dietary isoflavones alter regulatory behaviors, metabolic hormones and neuroendocrine function in Long-Evans male rats.

BACKGROUND: Phytoestrogens derived from soy foods (or isoflavones) have received prevalent usage due to their 'health benefits' of decreasing: a) age-related diseases, b) hormone-dependent cancers and c) postmenopausal symptoms. However, little is known about the influence of dietary phytoestrogens on regulatory behaviors, such as food and water intake, metabolic hormones and neuroendocrine parameters. This study examined important hormonal and metabolic health issues by testing the hypotheses that dietary soy-derived isoflavones influence: 1) body weight and adipose deposition, 2) food and water intake, 3) metabolic hormones (i.e., leptin, insulin, T3 and glucose levels), 4) brain neuropeptide Y (NPY) levels, 5) heat production [in brown adipose tissue (BAT) quantifying uncoupling protein (UCP-1) mRNA levels] and 6) core body temperature. METHODS: This was accomplished by conducting longitudinal studies where male Long-Evans rats were exposed (from conception to time of testing or tissue collection) to a diet rich in isoflavones (at 600 micrograms/gram of diet or 600 ppm) vs. a diet low in isoflavones (at approximately 10-15 micrograms/gram of diet or 10-15 ppm). Body, white adipose tissue and food intake were measured in grams and water intake in milliliters. The hormones (leptin, insulin, T3, glucose and NPY) were quantified by radioimmunoassays (RIA). BAT UCP-1 mRNA levels were quantified by PCR and polyacrylamide gel electrophoresis while core body temperatures were recorded by radio telemetry. The data were tested by analysis of variance (ANOVA) (or where appropriate by repeated measures). RESULTS: Body and adipose tissue weights were decreased in Phyto-600 vs. Phyto-free fed rats. Food and water intake was greater in Phyto-600 animals, that displayed higher hypothalamic (NPY) concentrations, but lower plasma leptin and insulin levels, vs. Phyto-free fed males. Higher thyroid levels (and a tendency for higher glucose levels) and increased uncoupling protein (UCP-1) mRNA levels in brown adipose tissue (BAT) were seen in Phyto-600 fed males. However, decreased core body temperature was recorded in these same animals compared to Phyto-free fed animals. CONCLUSIONS: This study demonstrates that consumption of a soy-based (isoflavone-rich) diet, significantly alters several parameters involved in maintaining body homeostatic balance, energy expenditure, feeding behavior, hormonal, metabolic and neuroendocrine function in male rats.

In Short: Rats fed high levels of soy isoflavones showed lower insulin levels, higher thyroid (T3) levels, higher glucose levels, and decreased body temperature.

SCIENCE: National Library of Medicine

Endocrine active compounds affect thyrotropin and thyroid hormone levels in serum as well as endpoints of thyroid hormone action in liver, heart and kidney.

To assess interference with endocrine regulation of the thyroid axis, rats (female, ovariectomised) were treated for 12 weeks with the suspected endocrine active compounds (EAC) or endocrine disrupters (ED) 4-nonylphenol (NP), octyl-methoxycinnamate (OMC) and 4-methylbenzylidene-camphor (4-MBC) as well as 17beta-estradiol (E2) and 5alpha-androstane-3beta,17beta-diol (Adiol) on the background of a soy-free or soy-containing diet, and endpoints relevant for regulation via the thyroid axis were measured. Thyrotropin (TSH) and thyroid hormone (T4, T3) serum levels were altered, but not in a way consistent with known mechanisms of feedback regulation of the thyroid axis. In the liver, malic enzyme (ME) activity was significantly increased by E2 and Adiol, slightly by OMC and MBC and decreased by soy, whereas type I 5'-deiodinase (5'DI) was decreased by all treatments. This may be due rather to the estrogenic effect of the ED, as there is no obvious correlation with T4 or T3 serum levels. None of the substances inhibited thyroid peroxidase (TPO) in vitro, except for NP. In general, several endocrine active compounds disrupt the endocrine feedback regulation of the thyroid axis. However, there was no uniform, obvious pattern in the effects of those ED tested, but each compound elicited its own spectrum of alterations, arguing for multiple targets of interference with the complex network of thyroid hormone action and metabolism.

In Short: In tests on rats, malic enzyme and I 5'-deiodinase was decreased by soy. Deiodinases convert T4 into T3.

What is Deiodinase?

REFERENCE: Wikipedia - Deiodinase

In the tissues, deiodinases can either activate or inactivate thyroid hormones. Activation occurs by conversion of the prohormone thyroxine (T4) to the active hormone triiodothyronine (T3) through the removal of an iodine atom on the outer ring.

SCIENCE: National Library of Medicine

Effect of dietary soy on serum thyroid hormone concentrations in healthy adult cats.

OBJECTIVE: To compare effects of short-term administration of a soy diet with those of a soy-free diet on serum thyroid hormone concentrations in healthy adult cats. ANIMALS: 18 healthy adult cats. PROCEDURE: Cats were randomly assigned to receive either a soy or soy-free diet for 3 months each in a crossover design. Assays included CBC, serum biochemical profile, thyroid hormone analysis, and measurement of urinary isoflavone concentrations. RESULTS: Genistein, a major soy isoflavone, was identified in the urine of 10 of 18 cats prior to dietary intervention. Compared with the soy-free diet, cats that received the soy diet had significantly higher total thyroxine (T4) and free T4 (fT4) concentrations, but unchanged total triiodothyronine (T3) concentrations. The T3/fT4 ratio was also significantly lower in cats that received the soy diet. Although the magnitudes of the increases were small (8% for T4 and 14% for fT4), these changes resulted in an increased proportion of cats (from 1/18 to 4/18) that had fT4 values greater than the upper limit of the laboratory reference range. There was no significant effect of diet on any other measured parameter. CONCLUSIONS AND CLINICAL RELEVANCE: Short-term administration of dietary soy has a measurable although modest effect on thyroid hormone homeostasis in cats. Increase in T4 concentration relative to T3 concentration may result from inhibition of 5'-iodothyronine deiodinase or enhanced T3 clearance. Soy is a common dietary component that increases serum T4 concentration in cats.

In Short: Cats receiving a soy diet had significantly higher T4 and free T4 concentrations but unchanged T3 concentrations. The increase of T4 to T3 may result from the inhibition of 5'-iodothyronine deiodinase.

SCIENCE: National Library of Medicine

Soy formula complicates management of congenital hypothyroidism.

AIMS: To test the hypothesis that feeding soy formula to infants with congenital hypothyroidism (CH) leads to prolonged increase of thyroid stimulating hormone (TSH). METHODS: The study was a review of 78 patients seen during their first year of life between 1990 and 1998. Data regarding clinical diagnosis, date of treatment initiation, TSH, levothyroxine dose, weight, length, and diet information from each visit were collected from the charts. RESULTS: There were eight patients in the soy diet group and 70 in the non-soy diet group. There was no significant difference between the two groups in the starting dose of levothyroxine or the change in this dose over one year. There was a significant difference between the two groups in the following areas: time to TSH normalisation, first TSH on treatment, percentage with increased TSH at 4 months of age, percentage with increased TSH throughout the first year of life, and in the overall trend of TSH at each visit. CONCLUSIONS: Infants fed soy formula had prolonged increase of TSH when compared to infants fed non-soy formula. These infants need close monitoring of free thyroxine and TSH measurements, and they may need increased levothyroxine doses to achieve normal thyroid function tests.

In Short: Infants fed soy formula had higher levels of TSH.

SCIENCE: National Library of Medicine

Goitrogenic and estrogenic activity of soy isoflavones.

Soy is known to produce estrogenic isoflavones. Here, we briefly review the evidence for binding of isoflavones to the estrogen receptor, in vivo estrogenicity and developmental toxicity, and estrogen developmental carcinogenesis in rats. Genistein, the major soy isoflavone, also has a frank estrogenic effect in women. We then focus on evidence from animal and human studies suggesting a link between soy consumption and goiter, an activity independent of estrogenicity. Iodine deficiency greatly increases soy antithyroid effects, whereas iodine supplementation is protective. Thus, soy effects on the thyroid involve the critical relationship between iodine status and thyroid function. In rats consuming genistein-fortified diets, genistein was measured in the thyroid at levels that produced dose-dependent and significant inactivation of rat and human thyroid peroxidase (TPO) in vitro. Furthermore, rat TPO activity was dose-dependently reduced by up to 80%. Although these effects are clear and reproducible, other measures of thyroid function in vivo (serum levels of triiodothyronine, thyroxine, and thyroid-stimulating hormone; thyroid weight; and thyroid histopathology) were all normal. Additional factors appear necessary for soy to cause overt thyroid toxicity. These clearly include iodine deficiency but may also include additional soy components, other defects of hormone synthesis, or additional goitrogenic dietary factors. Although safety testing of natural products, including soy products, is not required, the possibility that widely consumed soy products may cause harm in the human population via either or both estrogenic and goitrogenic activities is of concern. Rigorous, high-quality experimental and human research into soy toxicity is the best way to address these concerns. Similar studies in wildlife populations are also appropriate.

In Short: Rats administered a genistein-fortified diet had a significant inactivation of thyroid peroxidase (TPO). The reduction was dose-dependent and was reduced by up to 80%. T3, T4, and TSH levels were normal. Thyroid peroxidase is necessary for the creation of T4 and T3. Iodine deficiency increased soy antithyroid effects, and iodine supplementation was protective.

What is Thyroid Peroxidase?

The recipe for making thyroid hormones calls for two principle raw materials:

* Tyrosines are provided from a large glycoprotein scaffold called thyroglobulin, which is synthesized by thyroid epithelial cells and secreted into the lumen of the follicle - colloid is essentially a pool of thyroglobulin. A molecule of thyroglobulin contains 134 tyrosines, although only a handful of these are actually used to synthesize T4 and T3.

* Iodine, or more accurately iodide (I-), is avidly taken up from blood by thyroid epithelial cells, which have on their outer plasma membrane a sodium-iodide symporter or "iodine trap". Once inside the cell, iodide is transported into the lumen of the follicle along with thyroglobulin.

Fabrication of thyroid hormones is conducted by the enzyme thyroid peroxidase, an integral membrane protein present in the apical (colloid-facing) plasma membrane of thyroid epithelial cells. Thyroid peroxidase catalyzes two sequential reactions:

1. Iodination of tyrosines on thyroglobulin (also known as "organification of iodide").
2. Synthesis of thyroxine or triiodothyronine from two iodotyrosines.

Through the action of thyroid peroxidase, thyroid hormones accumulate in colloid, on the surface of thyroid epithelial cells. Remember that hormone is still tied up in molecules of thyroglobulin - the task remaining is to liberate it from the scaffold and secrete free hormone into blood.

Thyroid hormones are excised from their thyroglobulin scaffold by digestion in lysosomes of thyroid epithelial cells. This final act in thyroid hormone synthesis proceeds in the following steps:

* Thyroid epithelial cells ingest colloid by endocytosis from their apical borders - that colloid contains thyroglobulin decorated with thyroid hormone.

* Colloid-laden endosomes fuse with lysosomes, which contain hydrolytic enzymes that digest thyroglobluin, thereby liberating free thyroid hormones.

* Finally, free thyroid hormones apparently diffuse out of lysosomes, through the basal plasma membrane of the cell, and into blood where they quickly bind to carrier proteins for transport to target cells.

Control of Thyroid Hormone Synthesis and Secretion

Each of the processes described above appears to be stimulated by thyroid-stimulating hormone from the anterior pituitary gland. Binding of TSH to its receptors on thyroid epithelial cells stimulates synthesis of the iodine transporter, thyroid peroxidase and thyroglobulin.

So just what are these goitrogenic agents?  In 1997 research from the FDA's National Center for Toxicological Research (NCTR) showed that the darling of the soy industry, the isoflavone genistein, was a potent inhibitor of Thyroid Peroxidase (TPO); in fact genistein is a more powerful inhibitor of TPO than common anti-thyroid drugs!  If genistein could inhibit TPO in vitro, it follows that it could result in an elevation of Thyroid Stimulating Hormone (TSH), and a subsequent decrease in thyroxine (T3) in vitro; in other words consumption of the soy isoflavone genistein might result in hypothyroidism and goitre.

Recent research leaves little doubt that dietary isoflavones in soy have a profound effect on thyroid function in humans. A study by Japanese researchers concluded that intake of soy by healthy adults for a long duration caused enlargement of the thyroid and suppressed thyroid function. These researchers studied the effects of feeding 30 g of soybeans per day on thyroid function and found that after one month there was a significant increase in thyroid stimulating hormone (TSH) levels in a group of 20 adults (group I) but no change in thyroxine levels.

Diffuse goitre and hypothyroidism appeared in some of these subjects and about half of another group of 17 adults (group II) that took soybeans for 3 months. This group also had increased TSH levels, especially in older subjects, but once again there was no significant change in plasma thyroxine. After three months of soy intake other relevant symptoms included constipation (in 53% of subjects), fatigue (in 53% of subjects), lethargy (in 41% of subjects). It should be noted that iodine intake (via seaweed) was normal in all subjects.

The goitre was a diffuse goitre (degrees I and II enlargement) and occurred in 3 of group 1 and 8 (47%) of group 2. One subject in group 1 developed sub-acute thyroiditis. Two of the 11 subjects with goitre showed no reduction in goitre size one month after cessation of soy but goitre size was reduced in the other 9 subjects. The two subjects received thyroxine treatment and their goiters reduced in size after two and six months respectively.

The combination of a moderately elevated TSH with a normal free thyroxine defines subclinical hypothyroidism, a condition which may evolve towards overt hypothyroidism especially in persons with anti-thyroid antibodies. The condition is defined as the state in which a reduction in thyroid hormone secretion is compensated for by an increased TSH production to order maintain a clinically euthyroid status. Subclinical hypothyroidism is of increasing importance and its prevalence appears to be growing such that studies to define both its evolution and strategies for its management are warranted. Thyroid experts have noted that dietary factors may well play a major role in the development of this condition since high goitrogen intake can increase TSH secretion.

In Short: Genistein is a potent inhibitor of Thyroid Peroxidase (TPO). Long-time intake of soy causes raised TSH but no change in T4. These subjects experienced constipation, fatigue, and lethargy. After cessation of soy intake, levels returned to normal, either naturally or after thyroxine treatment. This is known as subclinical hypothyroidism.

SCIENCE: National Library of Medicine

Use of soy protein supplement and resultant need for increased dose of levothyroxine.

OBJECTIVE: To report a case of difficulty in achieving suppressive serum levels of thyroid hormone because of malabsorption of exogenous levothyroxine attributable to daily ingestion in close temporal relationship to the intake of a soy protein-containing food supplement. METHODS: We present the relevant history and laboratory data of the current case and provide supportive documentation from the literature. RESULTS: A 45-year-old woman who had hypothyroidism after a near-total thyroidectomy and radioactive iodine ablative therapy for papillary carcinoma of the thyroid required unusually high oral doses of levothyroxine to achieve suppressive serum levels of free thyroxine (T(4)) and thyrotropin (thyroid-stimulating hormone or TSH). She had routinely been taking a "soy cocktail" protein supplement immediately after her levothyroxine. Temporal separation of the intake of the soy protein cocktail from the administration of the levothyroxine resulted in attainment of suppressive serum levels of free T(4) and TSH with use of lower doses of levothyroxine. CONCLUSION: Administration of levothyroxine concurrently with a soy protein dietary supplement results in decreased absorption of levothyroxine and the need for higher oral doses of levothyroxine to attain therapeutic serum thyroid hormone levels.

In Short: Ingestion of soy proteins caused a T4 supplement to become less effective, thereby needing higher doses to get the same effect.

SCIENCE: National Library of Medicine

Energy metabolism and thyroid hormone levels of growing rats in response to different dietary proteins--soy protein or casein.

Energy balances were measured by indirect calorimetry in four experiments on male growing rats, fed restrictively on isoenergetic and isonitrogenous (10% CP) diets based on either casein supplemented with methionine, or soy protein isolate (experiments 1, 2 and 3) and soy protein isolate supplemented with methionine (experiment 0), respectively. At the end of experiments the rats were killed for body analysis and determination of thyroid hormones and lipids in blood as well as mitochondrial respiration in liver and heart. Feeding of non-supplemented soy protein resulted in a lower efficiency of energy utilisation as well as a lower protein utilisation compared to casein-fed and supplemented soy protein-fed rats. Chemical body composition was not markedly different between the dietary groups. After long-term feeding of soy protein (experiment 3) mass and mitochondrial protein content of the interscapular brown adipose tissue were increased compared to casein-fed rats. Serum thyroid hormone levels were not changed (T3 and free T3) or were significantly lowered (T4 and free T4) following soy protein feeding in comparison with casein feeding (except for experiment 2). Cholesterol and triglycerides were decreased on an average in response to soy protein or supplemented soy protein feeding. In two of three experiments a significant lower efficiency of hepatic mitochondrial respiration with succinate as substrate, expressed by the ratio of added ADP to oxygen consumed, was observed in soy protein-fed rats compared to casein-fed rats.

In Short: Feeding of soy protein isolate to rats caused a lower efficiency of energy and protein utilisation . T3 and free T3 levels were not changed but T4 and free T4 were significantly lower.

"As little as a 5- to 8-ounce serving of soy milk a day has been proven to suppress thyroid function," says soy researcher and nutritionist Michael Fitzpatrick. Drs. Daniel Sheehan and Daniel Doerge, former senior researchers at the Food and Drug Administration, have strongly opposed the soy industry's proclamation that this humble bean is king. In a 1999 letter, the two scientists stated that rather than tout its health benefits, the FDA should attach a warning label to soy products. "The possibility that widely consumed soy products may cause harm in the human population via either or both estrogenic and [thyroid] activity is of concern," said Sheehan in a recently published study.
The culprit in a high soy diet lies in the isoflavones found in the bean, in particular, genistein.
Gillespie speaks from firsthand experience. She first tried soy supplements at the recommended dose of 40 milligrams. "I went into full-blown hypothyroidism within 72 hours," she said. Next she experimented with tofu. "Same results as before, but this time it took me five days to get there."

Thirty milligrams of soy isoflavones can be found in:
• 7 ounces of soybeans
• 4 ounces of tofu
• 8 ounces of soy milk
• 1.6 ounces of miso
• 2.8 ounces of soybean sprouts

1,000 Faces of Soy

A great many foods already in your kitchen cupboard contain products that contain some type of soy food. Listed below are the terms associated with soy foods:

SCIENCE: National Library of Medicine

The ratio of genistein to daidzein isoflavone forms was higher in isolated soy protein-based versus "whole bean" soy milks (2.72 +/- 0.24 vs 1.62 +/- 0.47, respectively, p < 0.0001).

Common Phytoestrogens and Their Sources


Soybeans and soy products:

Soy flour, 1.65 - 130.92
Soybeans, raw, 9.89 - 124.20
   (A different assay measured 10.5 - 56.0)1
Soy protein isolate, 7.70 - 68.89
Miso, 7.10 - 36.64
Tempeh, 4.67 - 27.30
Tofu, 8.00 - 25.80
Soy cheese, 0.20 - 21.10
Soy milk, 1.14 - 9.84
Infant formulas, 0.75 - 9.65
Soy dog, 3.40
Shoyu, 0.60 - 1.40
Soy sausage, 0.75
Commercial soy sauce, 0.10
Soy oil, 0

Other sources:

Kudzu root, 1851
Split peas, raw, 0 - 7.26
   (A different assay measured 0.007 - 0.036)1
Red clover leaf** 4.25
Mung bean sprouts, 0.701
Kudzu leaf, 0.3751
Red clover seed, 0.1781
Sesame seed, 0.1401
Chick peas, raw, 0 - 0.08
   (A different assay measured 0.011 - 0.192)1
Alfalfa (mature) 0.0629
Peanuts, raw, 0.01 - 0.05
   (A different assay measured 0.058)1
Black-eyed peas, raw, 0 - 0.03
Pinto beans, raw, 0 - 0.02
Fenugreek seed, 0.01
Lentils, raw, 0 - 0.01
Alfalfa sprouts, 0
Black beans, raw, 0***
Kidney beans, cooked, 0
   (A different assay measured 0.007 - 0.040)1
Red clover sprouts, 0


Soybeans and soy products:

Soy flour, 2.75 - 145.23
Soybeans, raw, 13.00 - 138.24
   (A different assay measured 26.8 - 84.1)1
Soy protein isolate, 27.17 - 105.10
Miso, 11.70 - 52.39
Tofu, 11.10 - 42.15
Tempeh, 1.11 - 39.77
Soy cheese, 0.50 - 38.20
Infant formulas, 1.58 - 15.43
Soy milk, 1.12 - 11.28
Soy dog, 8.20
Soy sausage, 2.70
Shoyu, 0.30 - 1.54
Commercial soy sauce, 0
Soy oil, 0

Other sources:

Red clover leaf** 56.05
Kudzu root, 12.601
Kudzu leaf, 2.521
Mung bean sprouts, 2.001
Pinto beans, raw, 0.52
Peanuts, raw, 0.08 - 0.39
   (A different assay measured 0.064)1
red clover Sprouts, 0.35
Split peas, raw, 0 - 0.10
   (A different assay measured 0 - 0.023)1
Chick peas, raw,  0 - 0.12
   (A different assay measured 0.069 - 0.214)1
Black-eyed peas, raw,  0 - 0.03
Fenugreek seed, 0.01
Lentils, raw, 0 - 0.01
Alfalfa (mature), trace9
Alfalfa sprouts, 0
Black beans, raw, 0***
Kidney beans, cooked, 0
   (A different assay measured 0.018 - 0.518)1


Red clover (mature plant) - rich source; content varies by variety; used for commercial extraction. One group reported 1322 mg/100 g.4 A more recent analysis* detected 647 mg/100 g.5

One commercial red clover extract contains 40 mg mixed isoflavones/tablet (including 8 mg formononetin).6

Kudzu Root, 7.0901
Red clover sprouts, 2.281
Red clover seed, 1.2701
Alfalfa sprouts, 0.3410
Chickpeas, 0.094 - 0.2151
Soybeans, 0.018 - 0.1211
Kudzu Leaf, 0.0871
Alfalfa (mature), trace11
Red clover tea (flowering tops), trace7


Soybeans and soy products:

Soy protein isolate, 5.40 - 26.40
Soy flours, 3.95 - 28.8
Soy beans, raw, 6.72 - 20.40
Soy cheese, 2.70 - 4.10
Soy dogs, 3.40
Miso, 2.30 - 3.80
Infant formulas, 0.28 - 3.45
Tempeh, 0.90 - 3.20
Tofu, 1.70 - 2.90
Soymilk 0.36 - 0.86
Shoyu, 0.45
Soy sausage, 0.30
Soy oil, 0
Commercial soy sauce, 0

Soy protein also has concentrates and isolates. These refer to the process by which the proteins are produced, and the quality of the protein. Isolate is always a higher quality protein.

Soy protein concentrate are made from defatted soy beans, by removing most of the water soluble, non-protein ingredients. Most of the carbohydrates remain in soy protein concentrate, so it tends to have some soy bean flavors.

Soy protein isolates are the most pure and refined soy protein available. Soy protein isolates are made from defatted soy beans, with most other ingredients removed leaving almost all protein. Usually, soy protein isolates contain 90% + protein on a moisture free (dry) basis. Soy protein isolates will also be more 'neutral' flavored, compared to soy concentrates, mainly because almost everything else is removed except the protein. Unlike soy concentrate, the carbohydrates are also removed, so the soy bean taste is also removed.

Soy protein concentrate is made by removing a portion of the carbohydrates (sugars) from dehulled and defatted soybeans. There are different soy protein production methods. The most frequent method used is alcohol extraction although this method results in most loss of the soy isoflavones. However, when the water extraction method is used to remove the sugars, there is a good retention of the isoflavones in the final product.

REFERENCE: Wikipedia - Soy Protein

Soybeans are processed into three kinds of protein-rich products; soy flour, soy concentrate, and soy isolate.

In, January ,2006 an American Heart Association review(in the journal "Circulation") of a decade long study of soy protein benefits casts doubt on the FDA allowed "Heart Healthy" claim for soy protein. The panel also found that soy isoflavones DO NOT reduce post menopause "hot flashes" in women nor do isoflavones help prevent cancers of the breast, uterus or prostate. Thus, soy isoflavones in the form of supplements is not recommended. The panel does speculate that, "many soy products should be beneficial to cardiovascular and overall health because of their high content of polyunsaturated fats, fiber, vitamins, and minerals and low content of saturated fat."

Adverse Mental Effects of Soy

Adrenocortical effects of oral estrogens and soy isoflavones in female monkeys.
These findings suggest that long-term estrogen treatment may contribute to an androgen-deficient and hypercortisolemic state. 
Evidence for genistein mediated cytotoxicity and apoptosis in rat brain.
The effects of chronic treatment with high doses of genistein, a major isoflavone of soybeans and soy-based products, have yet to be determined and what is known remains controversial. The present study was undertaken to investigate the cytotoxic effects of chronic ingestion of genistein on rat brain in vivo and the observations were compared with results from in vitro studies with primary cultures of cortical neurons. Sprague-Dawley rats were given 2 or 20 mg/day genistein (p.o.) for four weeks. The high dose of genistein (20 mg/day) significantly increased lactate dehydrogenase (LDH) in rat brain tissue homogenates, whereas the low dose of genistein (2 mg/day) decreased LDH. In addition, DNA fragmentation was detected in homogenates of brain tissue from rats receiving either dose of genistein. These results are consistent with those of in vitro studies indicating that high concentrations of genistein caused cytotoxicity and DNA ladder formation in primary cultures of cortical neurons. Genistein decreased the expression of the 32 kDa caspase-3 precursor and increased the levels of cleaved caspase-3 (18 kDa) in both rat brain tissue homogenates and in primary cultures of cortical neurons. Furthermore, expression of poly (ADP-ribose) polymerase (PARP) was also decreased in both experimental systems. These results suggest that chronic administration of genistein at high doses may induce cytotoxicity and apoptosis in the rat brain.

In Short: Long-term exposure to genistein can lead to toxic brain effects.

Sheehan's concern about the effects of soy on cognitive function (detailed in his submission to the FDA opposing the Protein Technologies Health Claim Petition) is mainly based on the findings of Dr Lon White from the Honolulu:Asia Aging Study.   Long-term data (30+ years) from 7,000 men in a prospective epidemiological study in Hawaii showed an association between consistently high levels of tofu consumption in mid-life with low cognitive test scores and (independently) with Alzheimer's disease in late life.  Persons who reported eating tofu at least twice weekly had a 2.4 fold greater risk for development of Alzheimer's disease compared with persons reporting little tofu consumption.

The hippocampus is the area of the brain that is vital for learning and short-term memory.  Research by O'Dell shows that genistein inhibits development of this brain function. 

Soya phytoestrogens change cortical and hippocampal expression of BDNF mRNA in male rats.

Using in situ hybridisation, significant reductions were found in brain-derived neurotrophic factor (BDNF) mRNA expression in the CA3 and CA4 region of the hippocampus and in the cerebral cortex in the rats fed the diet containing phytoestrogens, compared with those on the soya-free diet.

This paper provides interesting reading when put into the context of the following paper.

Brain-derived neurotrophic factor is reduced in Alzheimer's disease.

Consistent with this hypothesis, a reduction in BDNF mRNA expression has been observed in human post-mortem Alzheimer's disease hippocampi.

We observed a reduction in the intensity and number of BDNF-immunoreactive cell bodies within both the Alzheimer's disease hippocampus and temporal cortex when compared to normal tissue. These results support and extend previous findings that BDNF mRNA is reduced in the human Alzheimer's disease hippocampus and temporal cortex, and suggest that a loss of BDNF may contribute to the progressive atrophy of neurons in Alzheimer's disease.

Neurobehavioral effects of dietary soy phytoestrogens.

These results indicate that consumption of dietary phytoestrogens resulting in very high plasma isoflavone levels (in many cases over a relatively short interval of consumption in adulthood) can significantly alter sexually dimorphic brain regions, anxiety, learning and memory. The findings of these studies identify the biological actions of phytoestrogens, specifically isoflavones and their metabolites, found in animal soy-containing diets on brain and behavior and implicate the importance of phytoestrogens given the recognized significance of estrogens in brain and neural disorders, such as Alzheimer's disease, especially in women.

Brain Aging and Midlife Tofu Consumption

Methods: The design utilized surviving participants of a longitudinal study established in 1965 for research on heart disease, stroke, and cancer. Information on consumption of selected foods was available from standardized interviews conducted 1965–1967 and 1971–1974. A 4-level composite intake index defined "low-low" consumption as fewer than two servings of tofu per week in 1965 and no tofu in the prior week in 1971. Men who reported two or more servings per week at both interviews were defined as "high-high" consumers. Intermediate or less consistent "low" and "high" consumption levels were also defined. Cognitive functioning was tested at the 1991–1993 examination, when participants were aged 71 to 93 years (n=3734). Brain atrophy was assessed using neuroimage (n=574) and autopsy (n=290) information. Cognitive function data were also analyzed for wives of a sample of study participants (n=502) who had been living with the participants at the time of their dietary interviews.

Results: Poor cognitive test performance, enlargement of ventricles and low brain weight were each significantly and independently associated with higher midlife tofu consumption. A similar association of midlife tofu intake with poor late life cognitive test scores was also observed among wives of cohort members, using the husband’s answers to food frequency questions as proxy for the wife’s consumption. Statistically significant associations were consistently demonstrated in linear and logistic multivariate regression models. Odds ratios comparing endpoints among "high-high" with "low-low" consumers were mostly in the range of 1.6 to 2.0.

Conclusions: In this population, higher midlife tofu consumption was independently associated with indicators of cognitive impairment and brain atrophy in late life.

New Findings May Support Soy-Dementia in Men

In April 2000, Lon White and others reported a dose-dependent positive correlation between tofu consumption and brain atrophy in a large sample of men over several decades. [1] While correlation does not prove causation, study size and duration along with the robust dose-dependent relationship caused me, even as a vegetarian, to avoid tofu and other soy products.

Correlation-based hypotheses should be tested against the availability of possible causal mechanisms. In addition to possible causal mechanisms previously cited by this author, [2] recent findings significantly increase the case for a causal mechanism of soy-induced brain atrophy.

Atrophic Pharmacology Indicated

Brain-derived neurotrophic factor (BDNF) facilitates the survival and genesis of brain cells. [3,4] The neuroprotective effects of caloric restriction are attributed in part to increased BDNF. [5] On the other hand, reduced BDNF is known to cause brain-cell atrophy and is associated with Alzheimer’s disease. [6,7] Now, a study in "Neuroscience Letters" reports that soy significantly reduced BDNF in the hippocampus and cerebral cortex of male rats. [8] Since reduced BDNF can cause neural atrophy, these findings appear to provide compelling evidence for a causal mechanism that might explain the positive correlation between tofu (soy) consumption and brain atrophy reported by White et al. [1]

Antisocial Effects of Soy

Increased aggressive behavior and decreased affiliative behavior in adult male monkeys after long-term consumption of diets rich in soy protein and isoflavones.

In the monkeys fed the higher amount of isoflavones, frequencies of intense aggressive (67% higher) and submissive (203% higher) behavior were elevated relative to monkeys fed the control diet (P's < 0.05). In addition, the proportion of time spent by these monkeys in physical contact with other monkeys was reduced by 68%, time spent in proximity to other monkeys was reduced 50%, and time spent alone was increased 30% (P's < 0.02).

The soya isoflavone content of rat diet can increase anxiety and stress hormone release in the male rat.

Isoflavones form one of the main classes of phytoestrogens and have been found to exert both oestrogenic and anti-oestrogenic effects on the central nervous system. The effects have not been limited to reproductive behaviour, but include effects on learning and anxiety and actions on the hypothalamo-pituitary axis. It is therefore possible that the soya content of diet could have significant effects on brain and behaviour and be an important source of between-laboratory variability.

Compared with the rats fed the iso-free diet, the rats fed the iso-150 diet spent significantly less time in active social interaction and made a significantly lower percentage of entries onto the open arms of the plus-maze, indicating anxiogenic effects in both animal tests. The groups did not differ in their basal corticosterone concentrations, but the iso-150 group had significantly elevated stress-induced corticosterone concentrations. Stress-induced plasma vasopressin concentrations were also significantly elevated in the iso-150 diet group compared with the iso-free rats.

Major changes in behavioural measures of anxiety and in stress hormones can result from the soya isoflavone content of rat diet. These changes are as striking as those seen following drug administration


Soy's Effect on Reproductive Systems

Chemical In Soy Alters Reproductive Organs In Male Rats

Researchers at the Johns Hopkins Children's Center and the Johns Hopkins Bloomberg School of Public Health report that male rats whose mothers were fed diets containing genistein, a chemical found in soybeans, developed abnormal reproductive organs and experienced sexual dysfunction as adults.

While these findings do not indicate that genistein has a similar effect in humans, researchers say the increasing popularity of soy and soy-based foods, such as tofu and some infant formulas, may warrant further research to determine if genistein exposure in the womb and during breast-feeding influences human reproductive development.

In the study, described in the April issue of the Journal of Urology, pregnant female rats were randomly assigned to one of three regimens: a genistein-free diet, a diet supplemented with a low dose of genistein, and a diet with a high dose of genistein.

Male offspring were exposed to genistein indirectly through maternal consumption during pregnancy and lactation.

When the genistein-exposed offspring matured, researchers found the males had smaller testes and a larger prostate gland compared to unexposed rats. Although their sperm counts were normal, exposed adult males had lower testosterone levels and were also less likely to ejaculate when presented with the opportunity to mate with a female.

"The effects of genistein continued long after the rats were exposed, leading us to believe that exposure to this plant-derived estrogen during reproductive development can have long-term detrimental effects in males," said the study's lead author, Amy B. Wisniewski, Ph.D., a researcher at the Johns Hopkins Children's Center.