Phytoestrogen content of foods--a compendium of literature values

A critical evaluation of the application of biomarkers in epidemiological studies on diet and health

One of the problems which may beset epidemiological studies is the difficulty of accurately measuring the dietary intakes of participants. Biomarkers of diet promise to provide a more accurate measure of dietary intake and a more objective one in that they are not reliant on the subject's memory. This review considers some issues of importance in epidemiology when information is obtained from biomarkers. The approach taken is to use examples both of normal dietary constituents and of contaminants in relation to a range of diet and health questions to illustrate these points. A brief overview of the role of sample collection, processing and storage is given including some generic recommendations for maximising the reliability of subsequent analytical data. Using the examples of phytoestrogens and iodine the question of whether biomarkers can accurately reflect the intake of the dietary constituents of interest at the population level or at the individual level is considered. The relationship of the biomarker to the natural history of the disease is exemplified using the role of folate in neural tube defects. Finally, intakes of vitamin D and heterocyclic amines are used to illustrate the integration of biomarkers into epidemiological studies of prostate and colorectal cancer, respectively. It is concluded that biomarkers may provide a more accurate and objective measure of diet than estimates of current or usual intake but that this approach also has limitations. A combination of methods will probably prove to be most valuable and this approach is being taken in current large prospective studies.

Estrogenic activity of two standardized red clover extracts (Menoflavon) intended for large scale use in hormone replacement therapy

Isoflavones are the most potent estrogenic compounds in red clover extracts. Standardized extracts have been discussed as an alternative for hormone replacement therapy. Variation due to extraction procedure and natural seasonal variation and variations originating from agricultural conditions have prevented the large scale use of such phytochemicals. An improved extraction procedure and careful analysis of the raw material yielded in a highly standardized preparation (Menoflavon) with an average isoflavone content of approximately 9% (dry weight) determined by HPLC. The estrogenic activity has been further evaluated by a yeast two plasmid system using estrogen receptor alpha (ER alpha) and estrogen receptor beta (ER beta). An estrogenic activity corresponding to a transactivational capacity of ca. 18 microg 17 beta-estradiol per g red clover extract for ER alpha and ca. 78 microg 17 beta-estradiol per g red clover for ER beta was obtained. The difference is explained by the higher affinity of ER beta to isoflavones than that observed for ER alpha. Calculation of potency from isoflavone content measured by HPLC yielded a comparable potency to that experimentally determined by the bioassay. The high content of isoflavones as well as the higher transactivational potency for ER beta than ER alpha make these extracts interesting candidates for HRT.

Soy intake and the maintenance of peak bone mass in Hong Kong Chinese women

Our previous study on bone health among premenopausal women showed that bone mass consolidation is attained by the early 30s, and small loss of spinal bone mineral density (SBMD) occurs soon after peak bone mass attainment. Recent interest has been shown in the potential beneficial effects of phytoestrogens on bone health. However, data are lacking, particularly in Asian women. This study aims to investigate the effect of soy isoflavones intake on the maintenance of peak bone mass in a cohort of 132 women aged 30-40 years who were followed up for 3 years. Baseline measurements of SBMD (L2-L4) were obtained using dual-energy X-ray densitometry, and dietary intake of soy foods and other key nutrients, including dietary calcium, were obtained through a quantitative food frequency method. Information on body measurements; physical activity (PA), weight-bearing activity in particular; age of menarche; and number of pregnancies were obtained at baseline. Repeated measurements of SBMD were obtained yearly for a further 3 years with an average follow-up time of 38 months. Analyses were performed on 116 subjects with at least three SBMD measurements (at baseline, 3-year follow-up, and at least one measurement during follow-up). The individual SBMD regression slope was computed for each of the subjects. Soy isoflavones consumption was categorized as quartiles of intake. We observed a significant difference in the SBMD individual regression slopes between women belonging to the fourth and first soy isoflavones intake quartiles. The positive effect of soy isoflavones on SBMD remained after adjusting for age and body size (height, weight, and bone area). Multiple linear regression analysis including the other known covariates (lean body mass, PA, energy adjusted calcium, and follow-up time) showed that soy isoflavones, together with these variables, accounted for 24% of the variances of the SBMD individual regression slope. This longitudinal study shows that soy intake had a significant effect on the maintenance of SBMD in women aged 30-40 years. The effects of phytoestrogens on bone health should be explored further in a population with habitual dietary soy but low calcium intake.

Soy isoflavone supplements antagonize reproductive behavior and estrogen receptor alpha- and beta-dependent gene expression in the brain

Epidemiological evidence suggests that isoflavone phytoestrogens may reduce the risk of cancer, osteoporosis, and heart disease, effects at least partially mediated by estrogen receptors alpha and beta (ERalpha and ERbeta). Because isoflavone dietary supplements are becoming increasingly popular and are frequently advertised as natural alternatives to estrogen replacement therapy, we have examined the effects of one of these supplements on estrogen-dependent behavior and ERalpha- and ERbeta-dependent gene expression in the brain. In the adult female rat brain, 17beta-estradiol treatment decreased ERbeta messenger RNA signal in the paraventricular nucleus by 41%, but supplement treatment resulted in a 27% increase. The regulation of ERbeta in the paraventricular nucleus is probably via an ERbeta-dependent mechanism. Similarly, in the ventromedial nucleus of the hypothalamus, supplement treatment diminished the estrogen-dependent up-regulation of oxytocin receptor by 10.5%. The regulation of oxytocin receptor expression in the ventromedial nucleus of the hypothalamus is via an ERalpha-dependent mechanism. Supplement treatment also resulted in a significant decrease in receptive behavior in estrogen- and progesterone-primed females. The observed disruption of sexual receptivity by the isoflavone supplement is probably due to antiestrogenic effects observed in the brain. These results suggest that isoflavone phytoestrogens are antiestrogenic on both ERalpha- and ERbeta-dependent gene expression in the brain and estrogen-dependent behavior.

Intake of dietary phytoestrogens is low in postmenopausal women in the United States: the Framingham study(1-4)

Many plants that are consumed contain phytoestrogens. Only a few published studies have examined the dietary intake of phytoestrogens in the general Western population. The potentially positive health effects of phytoestrogens might be of relevance to postmenopausal women. The aim of the present study was to estimate the intake of dietary isoflavones, coumestans and lignans by healthy Western postmenopausal women. For this purpose, we studied 964 postmenopausal, Caucasian women who participated in the Framingham Offspring Study and completed the Willett food-frequency questionnaire (FFQ). By searching the medical and agricultural literature and contacting experts, we identified food sources of phytoestrogens. The concentrations of the different isoflavones, coumestrol and lignans in each food in the FFQ were scored in seven categories and multiplied by the serving size of the food and the frequency of its consumption. The estimated daily median intake of the isoflavone daidzein was 39 microg (24-57 microg); of genistein, 70 microg (28-120 microg); of formononetin, 31 microg (13-44 microg); and of biochanin A, 6 microg (2-11 microg). Median total intake of isoflavones was 154 microg (99-235 microg). The main sources of isoflavones were beans and peas. The estimated daily intake of coumestans was 0.6 microg (0.2-1.7 microg), with broccoli as the main source. The estimated daily median intake of matairesinol was 19 microg (12-28 microg) and of secoisolariciresinol 560 microg (399-778 microg). The median total intake of lignans was 578 microg (416-796 microg). The main source of the lignans was fruits. The daily dietary intake of phytoestrogens in healthy postmenopausal Caucasian women in the United States is <1 mg.

Usual dietary isoflavone intake is associated with cardiovascular disease risk factors in postmenopausal women

Intervention data suggest a cardioprotective role for supplemental isoflavones; however, few studies have examined the cardiovascular disease (CVD) benefit of usual dietary isoflavone intake. This cross-sectional study examined the association between usual dietary isoflavone intake and CVD risk factors, including lipids and lipoproteins, body mass index (BMI) and fat distribution, blood pressure, glucose and insulin. Subjects were postmenopausal women (n = 208) aged 45-74 y, who attended screening and baseline visits for a randomized, double-blind, placebo-controlled trial examining the effects of isoflavone use. At screening, total cholesterol, triglycerides, HDL cholesterol and LDL cholesterol were measured, and demographic, behavioral and menopausal characteristics were assessed. One month later, dietary intake over the past year was assessed with a standardized questionnaire. Anthropometric measurements and blood pressure were obtained, and a 75-g oral glucose tolerance test was administered. Isoflavone consumption did not vary by age, exercise, smoking, education or years postmenopausal. Women with high genistein intake had a significantly lower BMI (P-trend = 0.05), waist circumference (P-trend = 0.05) and fasting insulin (P-trend = 0.07) than those with no daily genistein consumption. In adjusted analyses, genistein, daidzein and total isoflavone intake were each positively associated with HDL cholesterol (P = 0.05) and inversely associated with postchallenge insulin (P = 0.05). These data suggest a protective role for dietary soy intake against CVD in postmenopausal women.

Dietary phytoestrogen intake in mid-life Australian-born women: relationship to health variables

OBJECTIVES

To estimate the dietary intake of isoflavone-rich foods in a population-based cohort of Australia-born women, and to investigate whether a high intake of isoflavone-rich foods is associated with health-related variables.

METHOD

The study considered a population-based cohort of Australian-born women aged 51-62 years, with interviews, blood and physical measurements taken in their own homes. Food frequency questionnaires included usual eating habits and isoflavone-rich foods.

RESULTS

In total, 354 women (98%) returned both dietary questionnaires. Some 222 women (62%) reported consuming isoflavone-rich foods. Soy breads and milk provided the most servings per month. The mean intake of isoflavones calculated from soy beans, soy grits, tofu, soy milk, and soy and linseed bread in the whole cohort was 17 (standard deviation 35, range 0-340) mg/day. Fifty-one women (14%) consumed > 40 mg isoflavone/day. Compared with the rest of the cohort they had higher intakes of fruit, energy, protein, vitamins and minerals; ate a greater variety of vegetables; were more likely to exercise; were less likely to smoke; had lower mean body mass index, waist and hip measures and higher bone mineral density of the femoral neck; and had lower negative mood scores (all p < 0.05).

CONCLUSION

Australian-born women in Melbourne have a wide range of intake of isoflavone-rich foods. For those with a high intake it seems to be one component of a healthier life-style. It is thus not possible to assign particular health benefits to the one dietary component.

Intake of soy products is associated with better plasma lipid profiles in the Hong Kong Chinese population

We describe the pattern of soy intake and its association with blood lipid concentrations in the Hong Kong Chinese population. Subjects were contacted by random telephone survey and invited to a hospital for a physical examination and blood tests. A total of 500 men and 510 women with an age range of 24-74 y completed the dietary intake study. The dietary assessment was based on a semiquantitative food frequency questionnaire that included 10 commonly consumed soy items. Many (88%) of the study population had consumed some soy products during the previous week. About 80% of the soy protein or isoflavones were obtained from different forms of tofu, and an additional 9% was obtained from soy milk. The mean weekly isoflavone intake was 102 +/- 107 mg in men and 77 +/- 90 mg in women. In men, soy intake and total plasma cholesterol were negatively correlated (r = -0.09, P: = 0.04), as were soy intake and LDL cholesterol (r = -0.11, P: = 0.02). The respective values in women <50 y old were r = -0.11, P: = 0.04 and r = -0.11, P: = 0.05. Soy protein remained significantly associated with these two lipid concentrations after adjustment for other social and dietary confounders. Higher soy intake seemed to be related to a better plasma lipid profile in men and in younger women, but more epidemiological studies and controlled clinical trials in this setting would help to confirm the optimal amount required for the prevention and treatment of hyperlipidemia.

The therapeutic potential of phytoestrogens

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

Dietary intake and bioavailability of polyphenols

The main dietary sources of polyphenols are reviewed, and the daily intake is calculated for a given diet containing some common fruits, vegetables and beverages. Phenolic acids account for about one third of the total intake and flavonoids account for the remaining two thirds. The most abundant flavonoids in the diet are flavanols (catechins plus proanthocyanidins), anthocyanins and their oxidation products. The main polyphenol dietary sources are fruit and beverages (fruit juice, wine, tea, coffee, chocolate and beer) and, to a lesser extent vegetables, dry legumes and cereals. The total intake is approximately 1 g/d. Large uncertainties remain due to the lack of comprehensive data on the content of some of the main polyphenol classes in food. Bioavailability studies in humans are discussed. The maximum concentration in plasma rarely exceeds 1 microM after the consumption of 10-100 mg of a single phenolic compound. However, the total plasma phenol concentration is probably higher due to the presence of metabolites formed in the body's tissues or by the colonic microflora. These metabolites are still largely unknown and not accounted for. Both chemical and biochemical factors that affect the absorption and metabolism of polyphenols are reviewed, with particular emphasis on flavonoid glycosides. A better understanding of these factors is essential to explain the large variations in bioavailability observed among polyphenols and among individuals.

Isoflavone phytoestrogens consumed in soy decrease F(2)-isoprostane concentrations and increase resistance of low-density lipoprotein to oxidation in humans

BACKGROUND

Oxidative damage to lipids may be involved in the etiology of atherosclerosis, cardiovascular disease in general, and cancer. The soy isoflavone phytoestrogens, genistein and daidzein, and equol (a daidzein metabolite produced by intestinal microflora) are antioxidants in vitro; equol is a particularly good inhibitor of LDL oxidation and membrane lipid peroxidation.

OBJECTIVE

We sought to investigate the effects of a diet enriched with soy containing isoflavones on in vivo biomarkers of lipid peroxidation and resistance of LDL to oxidation, compared with a diet enriched with soy from which the isoflavones had been extracted.

DESIGN

: A randomized, crossover design was used to compare diets enriched with soy that was low or high in isoflavones in 24 subjects. Plasma concentrations of an F(2)-isoprostane, 8-epi-prostaglandin F(2)(alpha) (8-epi-PGF(2)(alpha)), a biomarker of in vivo lipid peroxidation, and resistance of LDL to copper-ion-induced oxidation were determined.

RESULTS

Plasma concentrations of 8-epi-PGF(2)(alpha) were significantly lower after the high-isoflavone dietary treatment than after the low-isoflavone dietary treatment (326 +/- 32 and 405 +/- 50 ng/L, respectively; P = 0.028) and the lag time for copper-ion-induced LDL oxidation was longer (48 +/- 2.4 and 44 +/- 1.9 min, respectively; P = 0.017). Lag time for oxidation of unfractionated plasma and plasma concentrations of malondialdehyde, LDL alpha-tocopherol, polyunsaturated fatty acids, and isoflavonoids did not differ significantly between dietary treatments.

CONCLUSIONS

Consumption of soy containing naturally occurring amounts of isoflavone phytoestrogens reduced lipid peroxidation in vivo and increased the resistance of LDL to oxidation. This antioxidant action may be significant with regard to risk of atherosclerosis, cardiovascular disease in general, and cancer.

Interindividual variation in metabolism of soy isoflavones and lignans: influence of habitual diet on equol production by the gut microflora

The soy isoflavones, daidzein and genistein, and the lignans, matairesinol and secoisolariciresinol, are phytoestrogens metabolized extensively by the intestinal microflora. Considerable important evidence is already available that shows extensive interindividual variation in isoflavone metabolism, and we have investigated the extent of this variation in a crossover study of a soy-containing food low or high in isoflavones (each treatment period lasted for 17 days, and the 2 treatment periods were separated by a 25-day washout period) in 24 healthy subjects [19 women and 5 men, mean age 30 yr, range 19-40, mean body mass index 22.5 +/- 3.5 (SD) kg/m2]. There was a 16-fold variation in total isoflavonoid excretion in urine after the high-isoflavone treatment period. The variation in urinary equol excretion was greatest (664-fold), and subjects fell into two groups: poor equol excretors and good equol excretors (36%). A significant negative correlation was found between the proportion of energy from fat in the habitual diet and urinary equol excretion (r = -0.55; p = 0.012). Good equol excretors consumed less fat as percentage of energy than poor excretors (26 +/- 2.3% compared with 35 +/- 1.6%, p < 0.01) and more carbohydrate as percentage of energy than poor excretors (55 +/- 2.9% compared with 47 +/- 1.7%, p < 0.05). Interindividual variation in the urinary excretion of O-desmethyl-angolensin (O-DMA) was also apparent (76-fold after the high-isoflavone treatment period), but there was no relationship between equol excretion and O-DMA excretion. Enterolactone was the major lignan metabolite in urine and plasma but showed less interindividual variation than equol and O-DMA. It is suggested that the dietary fat intake decreases the capacity of gut microbial flora to synthesize equol.

Daidzein and genistein content of fruits and nuts

Dietary phytoestrogens such as the isoflavones daidzein and genistein are thought to protect against chronic diseases that are common in Western societies, such as cancer, osteoporosis, and ischemic heart disease. In addition, there are concerns regarding the deleterious effects of hormone-like compounds, especially with respect to the development of infants. However, there is little information regarding the phytoestrogen content of foods, and therefore epidemiologic investigations of phytoestrogens are limited. As part of a study quantifying the consumption of phytoestrogens, the objective of this work was to assess the daidzein and genistein content of fruits and nuts commonly eaten in Europe. Eighty different fruits and nuts were sampled, prepared for eating, and freeze-dried. Daidzein and genistein were extracted from the dried foods, and the two isoflavones were quantified after hydrolytic removal of any conjugated carbohydrate. Completeness of extraction and any procedural losses of the isoflavones were accounted for using synthetic daidzin (7-O-glucosyl-4'-hydroxyisoflavone) and genistin (7-O-glucosyl-4'5-dihydroxyisoflavone) as internal standards. Of the 80 foods assayed, 43 contained no detectable daidzein or genistein, at a limit of quantification of 1 microg/kg dry weight of food. Nine foods contained more than 100 microg of the two isoflavones combined per kilogram wet weight, and 28 contained less than this amount. Currants and raisins were the richest sources of the isoflavones, containing 2,250 microg and 1,840 microg of the two isoflavones combined per kilogram of wet weight of food. Although fruits and nuts are not as rich in isoflavone phytoestrogens as are soy and other legumes, this is the first documentation of levels of daidzein and genistein occurring in these foods.

Soyfoods, soybean isoflavones, and bone health: a brief overview

Soyfoods have received considerable attention during the past 5 years for their role in disease prevention, especially in relation to heart disease, osteoporosis, and cancer. However, limited research also suggests that soy protein favorably affects renal function. Much of the research interest in soy is aimed at establishing the physiological effects of isoflavones. Isoflavones are diphenolic compounds that have a very limited distribution in nature. Soybeans and soyfoods are, for practical purposes, the only nutritionally relevant dietary sources of isoflavones. Isoflavones are weak estrogens in that they bind to estrogen receptors, but they also have important nonhormonal properties as well. Initial speculation that soyfoods, and in particular isoflavones, might promote bone health was based on the estrogenic properties of isoflavones and the similarity in structure between isoflavones and the osteoporosis drug, ipriflavone, which is a synthetic isoflavone. In ovariectomized rodents, isoflavones retard bone loss almost as effectively as estrogen. Most research, but not all, also indicates that soyfoods rich in isoflavones favorably affect bone turnover and spinal bone mineral density in perimenopausal and postmenopausal women. However, studies conducted thus far have been of short duration and involved small numbers of subjects. Furthermore, no studies have actually examined the effect of soy feeding on fracture risk. Thus, although the data in general are encouraging, no firm conclusions can be drawn about the relationship between soy consumption and bone health. In addition to a possible direct effect of isoflavones on bone tissue, soy protein when substituted for animal protein may indirectly enhance bone strength. Several studies have found that in comparison with animal protein, soy protein decreases calcium excretion, a result of the lower sulfur amino acid content of soy protein. Although the high potassium content of soy is a consideration, the evidence clearly indicates that clinicians should consider recommending that their renal patients incorporate soyfoods into their diet.

Brain aging and midlife tofu consumption

OBJECTIVE

To examine associations of midlife tofu consumption with brain function and structural changes in late life.

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.

The chemistry and biological activity of herbs used in Flor-Essence herbal tonic and Essiac

The herbal mixtures, Essiac and Flor-Essence, are sold as nutritional supplements and used by patients to treat chronic conditions, particularly cancer. Evidence of anticancer activity for the herbal teas is limited to anecdotal reports recorded for some 40 years in Canada. Individual case reports suggest that the tea improves quality of life, alleviates pain, and in some cases, impacts cancer progression among cancer patients. Experimental studies with individual herbs have shown evidence of biological activity including antioxidant, antioestrogenic, immunostimulant, antitumour, and antiocholeretic actions. However, research that demonstrates these positive effects in the experimental setting has not been translated to the clinical arena. Currently, no clinical studies of Essiac or Flor-essence are published, but a clinical study is being planned at the British Columbia Cancer Agency by the University of Texas-Center for Alternative Medicine (UT-CAM) and Tzu-Chi Institute for Complementary and Alternative Medicine.

Paracelsus to parascience: the environmental cancer distraction

Entering a new millennium seems a good time to challenge some old ideas, which in our view are implausible, have little supportive evidence, and might best be left behind. In this essay, we summarize a decade of work, raising four issues that involve toxicology, nutrition, public health, and government regulatory policy. (a) Paracelsus or parascience: the dose (trace) makes the poison. Half of all chemicals, whether natural or synthetic, are positive in high-dose rodent cancer tests. These results are unlikely to be relevant at the low doses of human exposure. (b) Even Rachel Carson was made of chemicals: natural vs. synthetic chemicals. Human exposure to naturally occurring rodent carcinogens is ubiquitous, and dwarfs the general public's exposure to synthetic rodent carcinogens. (c) Errors of omission: micronutrient inadequacy is genotoxic. The major causes of cancer (other than smoking) do not involve exogenous carcinogenic chemicals: dietary imbalances, hormonal factors, infection and inflammation, and genetic factors. Insufficiency of many micronutrients, which appears to mimic radiation, is a preventable source of DNA damage. (d) Damage by distraction: regulating low hypothetical risks. Putting huge amounts of money into minuscule hypothetical risks damages public health by diverting resources and distracting the public from major risks.

Validation of a novel estrogen receptor-based microtitration plate assay for the determination of phytoestrogens in soy-based foods

A novel, nonisotopic microtitration plate assay based on the human estrogen receptor has been used to screen soy-based and soy-containing foods for their phytoestrogen content (measured as genistein equivalents). The validation of the assay for use with food extracts has been demonstrated by investigation of recoveries after acidic and enzymic hydrolysis, by investigation of matrix effects, and by comparison of results with HPLC analysis. Phytoestrogen levels in soy products analyzed ranged between 520 and 1872 microgram of genistein equiv/g of soy flour, 5-282 microgram/g of soy concentrates, 503-1292 microgram/g of soy-protein isolates, and 108-226 microgram/g of soy-based infant formulas. Samples of textured vegetable protein and bread containing soy and linseed gave values of 1114 and 68 microgram/g, respectively. Comparison of results for 12 samples analyzed both by the receptor assay and by HPLC showed good correlation (r(2) = 0.905). The assay, which is rapid and simple to perform, is suitable for screening phytoestrogen-containing foods in order to assess human exposure to these bioactive compounds. The assay sensitivity is 3.4 microgram/g, and 14 samples/plate can be analyzed in 4 h following hydrolysis.

Cardiovascular and renal benefits of dry bean and soybean intake

Dry beans and soybeans are nutrient-dense, fiber-rich, and are high-quality sources of protein. Protective and therapeutic effects of both dry bean and soybean intake have been documented. Studies show that dry bean intake has the potential to decrease serum cholesterol concentrations, improve many aspects of the diabetic state, and provide metabolic benefits that aid in weight control. Soybeans are a unique source of the isoflavones genistein and diadzein, which have numerous biological functions. Soybeans and soyfoods potentially have multifaceted health-promoting effects, including cholesterol reduction, improved vascular health, preserved bone mineral density, and reduction of menopausal symptoms. Soy appears to have salutary effects on renal function, although these effects are not well understood. Whereas populations consuming high intakes of soy have lower prevalences of certain cancers, definitive experimental data are insufficient to clarify a protective role of soy. The availability of legume products and resources is increasing, incorporating dry beans and soyfoods into the diet can be practical and enjoyable. With the shift toward a more plant-based diet, dry beans and soy will be potent tools in the treatment and prevention of chronic disease.

Development of a simple method for the determination of genistein, daidzein, biochanin A, and formononetin (biochanin B) in human urine

A simple method was developed for the determination of free and/or total isoflavones daidzein, genistein, and their respective 4'-methoxy derivatives biochanin A and formononetin (biochanin B) at low levels in human urine. A solid-phase extraction on octadecyl silica (C(18)) columns was used for the isolation of the phytoestrogens from the matrix. An extraction on a ChemElut 1010 column connected on-line to a Florisil cartridge by a Teflon stopcock was used for effective eluate purification. A mixture of dichloromethane and ethyl acetate was used for elution of the isoflavones from the columns in tandem. The isoflavones were determined as trimethylsilyl (TMS) ethers using GC/MS-SIM after separation on an HP-5MS fused silica column. TMS ethers were obtained by using BSTFA containing 1% of TMCS. For the determination of free isoflavones 6-hydroxyflavone was used as internal standard, whereas robigenin was used in the case of total isoflavone determination. Recoveries for free isoflavones under study varied from 63.5 to 89.6% at the 25 ng mL(-)(1) level and from 63.5 to 89. 2% at the 5 ng mL(-)(1) level in urine. Analytical curves were linear between 5 and 25 ng mL(-)(1). Detection limits varied from 1 ng mL(-)(1) for formononetin to 2.3 ng mL(-)(1) for daidzein. Recoveries for total isoflavone determination after enzymatic hydrolysis with glucuronidase from Helix pomatia ranged from 56.5 to 77.1% at the 25 ng mL(-1) level.

The effects of phytoestrogens on human pancreatic tumor cells in vitro

Diet has been implicated as a possible link to the etiology, promotion and/or progression of many diseases, including cancer. Recently, interest has been focused on the cancer-protective role of several of the hormone-like diphenolic phytoestrogens, lignans, and isoflavonoids. This study examined the chemoprotective effects of genistein, biochanin A, equol, and coumestrol on human pancreatic adenocarcinoma cells in vitro. Two human adenocarcinoma cell lines, HPAF-11 from a male and Su 86.86 from a female, were used. HPAF-11 cells were exposed for 24 h to these agents at concentrations of 1 and 10 microM. Su 86.86 cells were exposed for 24 h at a concentration of 1 microM. Coumestrol and equol at higher concentrations were toxic to the Su 86.86 cells. These agents displayed marked differences between cell lines in inhibition of growth. Equol and coumestrol inhibited the growth of the female pancreatic tumor cells by 95%; however, these agents stimulated the growth of pancreatic tumor cells from the male. Genistein also stimulated growth in the male pancreatic tumor cells, but had little effect on pancreatic tumor cells from the female. Biochanin A inhibited growth of both male and female tumor cells, but to a lesser extent than other agents. This study also indicated a difference in K-ras expression in pancreatic tumors cells treated with these agents. Equol and coumestrol decreased K-ras expression in the female tumor cell line. Genistein increased expression of K-ras in both male and female pancreatic tumor cells. Genistein also increased expressions of the multidrug resistant (mdr-1) gene in the male tumor-cell line, while coumestrol and biochanin A decreased expression. Equol had no effect on mdr-1 expression. Whether the chemoprotective potential of equol and coumestrol against pancreatic cancer is greater in females than males is being further studied.

Isoflavones in retail and institutional soy foods

A national sampling plan was developed to select the most widely used isoflavone-containing foods in the United States. Foods were selected based on their retail volume and sampled in five geographical areas representing seven metropolitan areas. Isoflavones were analyzed from composite samples, raw and cooked, and reported by brand. Quality control measures were evaluated throughout the study. Isoflavone levels ranged from 1 microg/g in soy sauces to 540 microg/g in tempeh. Soymilk and tofu represented the major portion of soy foods evaluated. These data will appear in the electronic version of USDA Handbook No. 8 of Food Composition Data in 1999.

Development of a database for assessing dietary phytoestrogen intake

For the past two decades, epidemiologists have observed lower risks of lung, breast, prostate, colon, and other cancers in populations that frequently consume fruits and vegetables. Numerous phytoestrogens have been shown to be anticarcinogenic under experimental conditions and may account for at least part of the cancer-prevention effects of fruit and vegetable consumption. These plant constituents include isoflavonoids, coumestans, lignans, phytosterols, and flavonoids. DietSys, the nutrient analysis program associated with the National Cancer Institute Health Habits and History Questionnaire (HHHQ), and other nationally available nutrient analysis databases do not fully assess these constituents. Therefore, we modified DietSys to include these components in foods on the basis of published values. In addition, as part of an epidemiological study of prostate cancer, we modified the food-frequency component of the HHHQ to include the main foods contributing to phytoestrogen intake. Although there are limitations to the consistency and quality of many of the values because they were gathered from a variety of sources, our approach should provide a useful first tool for assessing the epidemiological association between phytoestrogen consumption and cancer risk. Furthermore, this work has already facilitated the identification of the major dietary contributors with phytoestrogen activity and prioritized future laboratory analyses of specific foods toward the development of a more complete and accurate database.

Optimal nutrition: fibre and phytochemicals

There is currently intense research interest in secondary plant metabolites because of their potential preventative effects on the chronic diseases of Western societies, especially cardiovascular disease and cancer. To date most of the research has focused on the identification of plant-derived substances and their potential protective effects against specific chronic diseases. The important issue of determining the optimal intake of those substances, such that the beneficial effects are maximized without manifestation of adverse effects, has yet to be addressed in most cases. Furthermore, there are no specific functional markers that can be used to assess optimal intake, although it may be possible to use biomarkers such as serum cholesterol if the rest of the diet is strictly controlled. The present review discusses a wide range of substances associated with plants, including dietary fibre, resistant starch, oligosaccharides, phyto-oestrogens, phytosterols, flavonoids, terpenes and isothiocyanates, and attempts where possible to indicate optimal intakes and to suggest functional markers.

Development of a soy food frequency questionnaire to estimate isoflavone consumption in US adults

OBJECTIVE

To develop a dietary assessment instrument to measure soy food consumption and isoflavone intake and test it for reliability.

DESIGN

A soy food frequency questionnaire, designed for use in this study, was administered twice to participants, separated by a 2-week interval. The questionnaire was tested for reproducibility of estimates of soy food consumption and isoflavone (genistein and daidzein) intake.

SUBJECTS/SETTING

A convenience sample of 51 faculty, staff, and students was recruited from a naturopathic university.

STATISTICAL ANALYSES PERFORMED

Intraclass correlation coefficients were used to assess reproducibility of estimates of soy food intake and genistein and daidzein intake.

RESULTS

Correlation coefficients comparing mean soy food servings per month between the 2 administrations of the questionnaire ranged from 0.50 for soy yogurt to 0.89 for tempeh. Correlation coefficients for genistein and daidzein intake estimated by the 2 administrations of the questionnaire were the same: 0.89. Mean intake (+/- standard deviation) of genistein and daidzein was 7 +/- 10 and 4 +/- 6 mg/day, respectively. Fifteen soy foods contributed 95% of the total genistein and daidzein intake: tofu, soy yogurt, tempeh, soy milk, low-fat tofu, soy flour, miso, soy protein isolate, low-fat soy milk, veggie soy burger, textured vegetable protein, miso soup, cooked soybeans, soy hot dogs, and natto (fermented soy beans).

APPLICATIONS

The soy food frequency questionnaire developed in this study provided highly reproducible estimates of soy food consumption and isoflavone intake. This instrument may be a useful tool in studies of the associations between isoflavone exposure and risk for chronic disease.

Dietary isoflavones: biological effects and relevance to human health

Substantial evidence indicates that diets high in plant-based foods may explain the epidemiologic variance of many hormone-dependent diseases that are a major cause of mortality and morbidity in Western populations. There is now an increased awareness that plants contain many phytoprotectants. Lignans and isoflavones represent two of the main classes of phytoestrogens of current interest in clinical nutrition. Although ubiquitous in their occurrence in the plant kingdom, these bioactive nonnutrients are found in particularly high concentrations in flaxseeds and soybeans and have been found to have a wide range of hormonal and nonhormonal activities that serve to provide plausible mechanisms for the potential health benefits of diets rich in phytoestrogens. Data from animal and in vitro studies provide convincing evidence for the potential of phytoestrogens in influencing hormone-dependent states; although the clinical application of diets rich in these estrogen mimics is in its infancy, data from preliminary studies suggest beneficial effects of importance to health. This review focuses on the more recent studies pertinent to this field and includes, where appropriate, the landmark and historical literature that has led to the exponential increase in interest in phytoestrogens from a clinical nutrition perspective.

The bioavailability of non-nutrient plant factors: dietary flavonoids and phyto-oestrogens

The bioavailability in human subjects of non-nutrient plant factors, including dietary flavonoids and phyto-oestrogens, is of great importance relative to their reported health protective effects. These effects include protection against heart disease, and also in the case of the phyto-oestrogens, hormone-dependent cancers. Epidemiological studies have shown flavonoid intake (mostly quercetin) to be inversely associated with mortality from CHD. Quercetin is a potent antioxidant in vitro, and protection against the oxidative damage to LDL implicated in atherogenesis has been suggested as a possible mechanism. Human subjects can absorb significant amounts of quercetin (particularly in the glucoside form) and it would appear to be sufficiently bioavailable to act as an antioxidant in vivo; however, following our recent study (J O'Reilly, TAB Sanders and H Wiseman, unpublished results), it is currently less clear whether quercetin really can act as an antioxidant in vivo. The isoflavone phyto-oestrogens genistein and daidzein are much less effective antioxidants than quercetin in vitro, however, they are well-absorbed by human subjects and appear to be sufficiently bioavailable to act as antioxidants in vivo. In our recent study (O'Reilly et al. 1998) lower plasma isoprostane concentrations and increased resistance of LDL to oxidation were observed following the high-isoflavone dietary phase compared with the low-isoflavone dietary phase. Considerable inter-individual variation in isoflavone metabolite excretion has been observed, in particular the production of equol (the gut bacterial metabolite of daidzein; a more potent antioxidant and more oestrogenic than daidzein), and this appears to be influenced by habitual diet. Further studies on the bioavailability of these non-nutrient plant factors and related influencing factors are clearly still required.

Effect of isoflavone genistein on insulin receptors in perfused liver of ovariectomized rats

The experiments were carried out on ovariectomized Wistar rats. Their livers were perfused with basic perfusion medium (BPM) or BPM supplemented with isoflavone genistein, insulin or combination of the two factors. The obtained results support the hypothesis that genistein influences the kinetics of insulin binding to cell membranes changing the number of insulin receptors and dissociation constant (Kd). BPM supplementation with genistein decreased number of high affinity insulin receptors (HAIR) both in livers treated and untreated with insulin. The amount of HAIR diminished significantly from 610 +/- 77 x 10(-15) (no genistein) to 238 +/- 72 x 10(-15) mol/mg of membrane protein (supplement of genistein). Similarly, genistein reduced slightly the amount of HAIR even when added together with insulin (372 +/- 59 x 10(-15) mol/mg) in comparison to rats perfused with medium containing insulin but not the isoflavone (421 +/- 46 x 10(-15) mol/mg). Simultaneously, genistein decreased significantly Kd for HAIR (perfusion with BPM--1.44 +/- 0.18 x 10(-9) mol/l; perfusion with BMP + genistein--0.83 +/- 0.20 x 10(-9) mol/l). Such effects of genistein during liver perfision did not take place when the liver membranes were in vitro incubated with this xenobiotic.

Dietary intake and sources of isoflavones among Japanese

We examined the dietary intake and sources of isoflavones (daidzein and genistein) among Japanese subjects based on dietary records (DRs). The subjects comprised two groups: 1,232 who completed one-day DRs (Group 1) and 88 men and women who kept four four-day (16-day) DRs. For quantitative data on the level of daidzein and genistein in soy foods, we extensively reviewed the literature, particularly for Japanese soy foods, and adopted the median value for each food. The median intake of daidzein was 12.1 and 9.5 mg/day among Groups 1 and 2, respectively, while the corresponding values for genistein were 19.6 and 14.9 mg/day. The top four foods (tofu, miso, natto, and fried tofu) covered about 90% of the population intake of daidzein and genistein. It did not seem feasible to estimate one's intake of isoflavones by using dietary recording/recall in epidemiological studies, since the day-to-day variation in intake was too large, the within-person coefficient of variation being 89.1% for daidzein and genistein. Therefore, we should use other methods, such as food-frequency questionnaires, focusing on the four major sources of isoflavones, to assess individual isoflavone intake.

Phytoestrogens and breast cancer

Phytoestrogens are paradoxical. Because of their structural similarity to the physiological oestrogens, they have been assumed to increase the risk of breast cancer. However, nations where the largest amounts of phytoestrogens are consumed in the diet have the lowest incidence of and rate of death from breast cancer. Although these epidemiological observations do not prove that phytoestrogens have anti-cancer properties, many preclinical experiments support this concept. Some indicate that early life exposure to phytoestrogens may be critical for breast cancer prevention. Clinical studies to define the effect of phytoestrogens on breast cancer recurrence are underway. The recent discovery of a second class of oestrogen receptors, with a differential distribution among the tissues, may enable an explanation of the phytoestrogen paradox. These receptors have opened a way of utilizing phytoestrogens in the treatment of oestrogen-sensitive chronic diseases such as atherosclerosis and osteoporosis.

Soyfoods, isoflavones and risk of colonic cancer: a review of the in vitro and in vivo data

Soy foods and soybean components have received considerable attention of late for their potential role in reducing cancer risk. Although the relationship between soy intake and the risk of breast and prostate cancer has been the focus of most interest, the relationship between soy intake and other cancers, including colorectal cancer, has also been studied. Several anti-carcinogens have been identified in soybeans, but most enthusiasm for the potential anti-cancer effects of soy undoubtedly stems from work involving soybean isoflavones. Isoflavones have a limited distribution in nature, and, for practical purposes, soyfoods are the only nutritionally relevant dietary source of these phytochemicals. Isoflavones are weak oestrogens but possess other potentially important biological attributes independent of their ability to bind to the oestrogen receptor. The isoflavone genistein inhibits the growth of most types of hormone-dependent and hormone-independent cancer cells in vitro, including colonic cancer cells. Several mechanisms for the in vitro anti-cancer effects of genistein have been proposed, including effects on signal transduction. A number of epidemiological studies, primarily of Asian origin, have examined the relationship between soy intake and the risk of colorectal cancer. Although these studies provide little support for a protective effect of soy, concerns have been raised about the completeness of the soy intake data, since soy was not the focus of these studies and most of this research was conducted prior to the recent interest in the anti-cancer effects of soy. The effect of soy/isoflavone intake has also been studied in rodents, but again these data are conflicting and provide only modest support for a protective effect. Although the relationship between soy intake and colonic cancer risk is certainly worthy of further investigation, there is, at the moment, very limited support for soy exerting a protective effect against this type of cancer.

Nutritional and socioeconomic factors in relation to prostate cancer mortality: a cross-national study

BACKGROUND

Large international variations in rates of prostate cancer incidence and mortality suggest that environmental factors have a strong influence on the development of this disease. The purpose of this study was to identify predictive variables for prostate cancer mortality in data from 59 countries.

METHODS

Data on prostate cancer mortality, food consumption, tobacco use, socioeconomic factors, reproductive factors, and health indicators were obtained from United Nations sources. Linear regression models were fit to these data. The influence of each variable fit in the regression models was assessed by multiplying the regression coefficient b by the 75th (X75) and 25th (X25) percentile values of the variable. The difference, bX75 - bX25, is the estimated effect of the variable across its interquartile range on mortality rates measured as deaths per 100000 males aged 45-74 years. Reported P values are two-sided.

RESULTS

Prostate cancer mortality was inversely associated with estimated consumption of cereals (bX75 - bX25 = -7.31 deaths; P = .001), nuts and oilseeds (bX75 - bX25 = -1.72 deaths; P = .003), and fish (bX75 - bX25 = -1.47 deaths; P = .001). In the 42 countries for which we had appropriate data, soy products were found to be significantly protective (P = .0001), with an effect size per kilocalorie at least four times as large as that of any other dietary factor. Besides variables related to diet, we observed an association between prostate cancer mortality rates and a composite of other health-related, sanitation, and economic variables (P = .003).

CONCLUSIONS

The specific food-related results from this study are consistent with previous information and support the current dietary guidelines and hypothesis that grains, cereals, and nuts are protective against prostate cancer. The findings also provide a rationale for future study of soy products in prostate cancer prevention trials.

Extraction and quantification of daidzein and genistein in food

A simple analytical method has been developed for routine quantification of a broad range of concentrations of the isoflavones daidzein and genistein in food. The synthetic glucosides daidzin and genistin were used as internal standards, combined with each food prior to extraction. The recovery of the aglycones daidzein and genistein from these internal standards were used to ensure the completeness of the extraction and aid quantification of isoflavones from the food. Hydrolytic enzymes from Aspergillus niger were used, in aqueous buffer, to liberate daidzein and genistein from their respective glycosides. The aglycone isoflavones were partitioned from the aqueous buffer into ethyl acetate. After evaporation of the ethyl acetate under nitrogen, the isoflavones were derivatized with N-tert-(butyldimethylsilyl)-N-methyltrifluoroacetamide and quantified by comparison with authentic synthetic standards using gas chromatography-mass spectrometry in selected ion mode. The isoflavone content of a stock soy flour was determined, using 36 separate assays, to be 1.05 mg daidzein and 1.11 mg genistein per gram of freeze-dried food, and the interassay coefficient of variation was 2.7 and 4.7, respectively.

Use of the Trolox assay to estimate the antioxidant content of seventeen edible wild plants of Niger

Although wild edible plants of the western Sahel and other parts of sub-Saharan Africa are consumed to some extent at all times of the year, greater amounts are consumed when cereal harvests are insufficient to support the populations living in these areas. The purpose of this study was to use a recently reported Trolox-based assay to measure the total antioxidant capacity of aqueous extracts of 17 plants that we gathered from southern Niger. The antioxidant contents of the aqueous extracts were compared to those of spinach and potato. Of the 17 plants, 11 had a greater antioxidant content than spinach and 14 had a greater antioxidant content than potato. The leaves of Tapinanthus globiferus had the greatest antioxidant content, and the fruit of Parinari macrophylla had the lowest. In general, leaves contained more antioxidants than either fruits or seeds. The total antioxidant capacity of the aqueous extracts was relatively high, indicating that the wild plants of the western Sahel may contain substantial amounts of water-soluble flavonoid glycosides, which are potent antioxidants and have been shown to have anticancer properties.

Isoflavones, soy-based infant formulas, and relevance to endocrine function

For more than 60 years, soy-based infant formulas have been fed to millions of infants worldwide and studied in controlled clinical research. These products provide essential nutrients required for normal growth and development. The safety of isoflavones in soy-based products, including infant formulas, has been questioned recently owing to reports of possible endocrine effects in animals and in cultured cells. The literature offers no evidence of endocrine effects in humans from infant consumption of modern soy-based formulas. Growth is normal and no changes in the timing of puberty or in fertility rates have been reported in humans who consumed soy formulas as infants. Consequently, soy-based infant formulas continue to be a safe, nutritionally complete feeding option for most infants.

Usual consumption of plant foods containing phytoestrogens and sex hormone levels in postmenopausal women in Wisconsin

Consumption of phytoestrogens may reduce hormone-dependent cancer risk through alterations in the actions or metabolism of steroid hormones. Studies in humans of phytoestrogen-hormone interactions have been limited and inconsistent. Relations between the consumption of phytoestrogen-containing foods and serum sex hormones and sex hormone-binding globulin were studied in a population-based sample of postmenopausal women who participated in the Nutritional Factors in Eye Disease Study of the Beaver Dam Eye Study. Information on phytoestrogen-containing foods (broccoli, carrots, cauliflower, chili, dark bread, peas, and dried beans) was collected by interviewer-administered food-frequency questionnaires. Estrone, sex hormone-binding globulin, dehydroepiandrosterone sulfate, and total and free testosterone were measured. Analyses included 246 postmenopausal women not taking hormone replacements. Partial correlations between hormones and intake of phytoestrogen-containing foods were computed, with adjustment for age, body mass index, years since menopause, and total energy intake. Number of standard servings per week of whole-grain products from the dark bread group was inversely associated with total testosterone (r = -0.20, p = 0.002). Although not statistically significant, other hormones displayed similar inverse associations with dark bread consistent with a common metabolic pathway. Although the magnitude of association was small, the data are consistent with the possibility that consumption of some phytoestrogen-containing foods may affect levels of testosterone in postmenopausal women.

Taxonomic classification helps identify flavonoid-containing foods on a semiquantitative food frequency questionnaire

We describe foods on the National Cancer Institute (NCI) semiquantitative food frequency questionnaire with respect to their botanical taxonomic classification and the likely presence of flavonoids. Foods listed in the NCI questionnaire were classified for potential flavonoid content using information from Linnaean taxonomic classification and processing techniques known to modify flavonoid content. The outcome measure was flavonoid presence in foods as evidenced in the food composition analytical literature. We then verified the presence of 6 classes of flavonoids in these foods by searching the chemical analytical literature (represented by Food Science and Technology Abstracts Service from January 1969 to June 1996). One hundred ninety foods were mentioned on the NCI questionnaire; after duplications were removed, 153 foods remained. Data obtained from literature searches indicated that 54 foods (35%) contained flavonoids. An additional 19 recipe foods (12%) had flavonoid-containing components or ingredients. Thirty-nine foods (25%) had flavonoids that had been reduced or removed during milling and other processing. Seven foods (5%) were stripped and judged to have no flavonoids. Thirty-four foods (22%), for example, dairy, meat, and sugar, were completely devoid of flavonoids. When food composition data are unavailable, botanical taxonomic classifications may be helpful in ascertaining the likely presence of flavonoids in foods. However, quantitative estimates are likely to be imprecise.

The prevention of cancer

1. The major causes of cancer are as follows: (a) Smoking: about a third of U.S. cancer (90% of lung cancer). (b) Dietary imbalances, e.g., lack of dietary fruits and vegetables: The quarter of the population eating the least fruits and vegetables has double the cancer rate for most types of cancer compared to the quarter eating the most; micronutrients may account for much of the protective effect of fruits and vegetables. Excess calories may also contribute to cancer. (c) Chronic infections: mostly in developing countries. (d) Hormonal factors influenced by life-style. 2. There is no epidemic of cancer, except for lung cancer due to smoking. Cancer mortality rates have declined 16% since 1950 (excluding lung cancer and adjusted for the increased life span of the population). 3. Regulatory policy that is focused on traces of synthetic chemicals is based on misconceptions about animal cancer tests. Recent research contradicts these ideas: (a) Rodent carcinogens are not rare. Half of all chemicals tested in standard high-dose animal cancer tests, whether occurring naturally or produced synthetically, are "carcinogens." (b) There are high-dose effects in these rodent cancer tests that are not relevant to low-dose human exposures and which can explain the high proportion of carcinogens. (c) Though 99.9% of the chemicals humans ingest are natural, the focus of regulatory policy is on synthetic chemicals. Over 1000 chemicals have been described in coffee: 27 have been tested and 19 are rodent carcinogens. Plants that we eat contain thousands of natural pesticides which protect plants from insects and other predators: 64 have been tested and 35 are rodent carcinogens. 4. There is no convincing evidence that synthetic chemical pollutants are important for human cancer. Regulations that try to eliminate minuscule levels of synthetic chemicals are enormously expensive: EPA estimates that total expenditures on environmental regulations cost $140 billion/year. It has been estimated by others that the United States spends 100 times more to prevent one hypothetical, highly uncertain death from a synthetic chemical than it spends to save a life by medical intervention. Attempting to reduce tiny hypothetical risks also has costs; for example, if reducing synthetic pesticides makes fruits and vegetables more expensive, thereby decreasing consumption, then cancer will be increased. 5. Improved health will come from knowledge due to biomedical research and from life-style changes by individuals. Little money is spent on biomedical research or on educating the public about lifestyle hazards, compared to the cost of regulations.

Phyto-oestrogens: where are we now?

Phyto-oestrogens have emerged from their esoteric role in animal husbandry following the hypothesis that the human Western diet is relatively deficient in these substances compared with societies where large amounts of plant foods and legumes are eaten. Evidence is beginning to accrue that they may begin to offer protection against a wide range of human conditions, including breast, bowel, prostate and other cancers, cardiovascular disease, brain function, alcohol abuse, osteoporosis and menopausal symptoms. Of the two main classes of these weak oestrogens, the isoflavones are under intensive investigation due to their high levels in soyabean. Like the 'anti-oestrogen' Tamoxifen, these seem to have oestrogenic effects in human subjects in the cardiovascular system and bone. Although previously only available from food, isoflavones are now being marketed in health-food supplements or drinks, and tablets may soon be available over the counter as 'natural' hormone-replacement therapy. In cancer, anti-oestrogenic effects are thought to be important, although genistein especially has been shown to induce wide-ranging anti-cancer effects in cell lines independent of any hormone-related influence. There are few indications of harmful effects at present, although possible proliferative effects have been reported. In infants, the effects of high levels in soya milk formulas are uncertain. The second group, lignans, have been less investigated despite their known antioestrogenic effects and more widespread occurrence in foods. Investigation of the possible benefits of phyto-oestrogens is hampered by lack of analytical standards and, hence, inadequate methods for the measurement of low levels in most foods. This problem may prove to be a major dilemma for regulatory authorities, clinicians and others wishing to advise the general public on whether these compounds really do have the health benefits attributed to them.