Soy isoflavone supplementation elevates erythrocyte superoxide dismutase, but not plasma ceruloplasmin in postmenopausal breast cancer survivors

Modulation of the ubiquitin-proteasome system by phytochemicals: Therapeutic implications in malignancies with an emphasis on brain tumors

Regarding the multimechanistic nature of cancers, current chemo- or radiotherapies often fail to eradicate disease pathology, and frequent relapses or resistance to therapies occur. Brain malignancies, particularly glioblastomas, are difficult-to-treat cancers due to their highly malignant and multidimensional biology. Unfortunately, patients suffering from malignant tumors often experience poor prognoses and short survival periods. Thus far, significant efforts have been conducted to discover novel and more effective modalities. To that end, modulation of the ubiquitin-proteasome system (UPS) has attracted tremendous interest since it affects the homeostasis of proteins critically engaged in various cell functions, for example, cell metabolism, survival, proliferation, and differentiation. With their safe and multimodal actions, phytochemicals are among the promising therapeutic tools capable of turning the operation of various UPS elements. The present review, along with an updated outline of the role of UPS dysregulation in multiple cancers, provided a detailed discussion on the impact of phytochemicals on the UPS function in malignancies, especially brain tumors.

Oxidative stress, antioxidants, hormesis and calorie restriction: The current perspective in the biology of aging

Aging, in a large measure, has long been defined as the resultant of oxidative stress acting on the cells. The cellular machinery eventually malfunctions at the basic level by the damage from the processes of oxidation and the system starts slowing down because of intrinsic eroding. To understand the initial destruction at the cellular level spreading outward to affect tissues, organs and the organism, the relationship between molecular damage and oxidative stress is required to understand. Retarding the aging process is a matter of cumulatively decreasing the rate of oxidative damage to the cellular machinery. Along with the genetic reasons, the decrease of oxidative stress is somehow a matter of lifestyle and importantly of diet. In the current review, the theories of aging and the understanding of various levels of molecular damage by oxidative stress have been emphasized. A broader understanding of mechanisms of aging have been elaborated in terms of effects of oxidative at molecular, mitochondrial, cellular and organ levels. The antioxidants supplementation, hormesis and calorie restriction as the prominent anti-aging strategies have also been discussed. The relevance and the efficacy of the antiaging strategies at system level have also been presented.

Higher dietary soy intake appears inversely related to breast cancer risk independent of estrogen receptor breast cancer phenotypes

The relationship between soy intake (SI) and breast cancer (BC) has been widely investigated with limited information on the significance of hormone receptor status of BC on the association. This study assessed the relationship between SI and BC risk in the context of oestrogen receptor (ER) status of BC. We meta-analyzed data from published studies on SI and BC after a methodical search of EMBASE, PubMed and Cochrane Library through December 2019. Summary estimates with 95% confidence intervals (CI) were presented using a random-effects model. Eighteen (5 cohorts and 13 case-control) studies, were included in this meta-analysis and SI was inversely associated with BC risk [OR (95%) for highest vs. lowest soy food intake = 0.88 (0.84-0.92), P < 0.001, I ² = 76.1%, Egger's p-value = 0.425] among all women. The inverse relationship was stronger among premenopausal women [OR (95%) = 0.79 (0.71-0.87), P < 0.001, I ² = 77.3%, Egger's p-value = 0.644]. In addition, SI was inversely associated with BC risk among ER-negative (-) BC women [OR (95%) = 0.71 (0.57-0.90), P = 0.013, I ² = 72.0%, Egger's p-value = 0.355] and among ER-positive (+) BC women [OR (95%) = 0.87 (0.79-0.96), P = 0.008 I ² = 74.6%, Egger's p-value = 0.061]. SI appears inversely associated with BC risk, with a stronger inverse association among pre-menopausal and ER-negative BC women.

The effects of isoflavone supplementation plus combined exercise on salivary markers of oxidative stress in postmenopausal women

This study tested the effect of isoflavone supplementation in addition to combined exercise training in salivary oxidative stress markers in non-obese postmenopausal women. Thirty-two postmenopausal women without hormone therapy were randomly assigned to exercise + placebo (n = 15) or exercise + isoflavone supplementation (n = 17) groups. They performed 30 sessions of combined exercises (aerobic plus resistance) over ten weeks and consumed 100 mg of isoflavone supplementation or placebo. Saliva samples were collected after an overnight fast. Superoxide dismutase, total antioxidant capacity, thiobarbituric acid reactive substances, catalase, total protein and nitrite were determined before and after ten weeks of the intervention. The ANOVA two-way analysis of variance was applied with α of 5%. Both groups increase (p<0.05) superoxide dismutase activity and decrease catalase levels. There was interaction (time × group) in both nitrite and thiobarbituric acid reactive substances results, with increase (p<0.05) in placebo group and decrease (p<0.05) in isoflavone group. No difference was found for total antioxidant capacity or total protein. The combination of isoflavone supplementation and exercise training can promote an antioxidant effect through reduction of lipid peroxidation and concentrations of salivary nitrite.

Soy isoflavone-loaded alginate microspheres in thermosensitive gel base: attempts to improve wound-healing efficacy

OBJECTIVES

This study aims to develop thermosensitive gel containing soy isoflavone (antioxidant and anti-inflammatory natural agent) alginate microspheres for enhancement of wound-healing performance.

METHODS

Soy isoflavone microspheres were prepared by ionic cross-linking method and optimized using the Box-Behnken optimization design. Formulations were characterized in terms of particle size, encapsulation efficiency and equilibrium swelling degree. The optimized formula was incorporated in Pluronic F127 gel base and examined for in vivo wound-healing efficacy.

KEY FINDINGS

Results showed mean particle size between 18 and 25 μm, encapsulation efficiency of over 75% and equilibrium swelling degree over 1.9. Thermal analysis indicated interaction between alginate and CaCl2 and embedding of soy isoflavone in microspheres. In vivo wound-healing efficacy showed significant advance in re-epithelization, mature collagen synthesis and proangiogenesis. Immunohistochemical investigation exhibited promising alpha-smooth muscle actin immunopositive cells expression, fibroblast activation and expression of proliferating cell nuclear antigen (proliferation marker) in the epidermis and in the dermis.

CONCLUSIONS

The developed formulation would appear to be a promising topical preparation for accelerating healing process.

The Effects of Isoflavone Supplementation Plus Combined Exercise on Lipid Levels, and Inflammatory and Oxidative Stress Markers in Postmenopausal Women

This study tested the effect of isoflavone supplementation in addition to combined exercise training on plasma lipid levels, inflammatory markers and oxidative stress in postmenopausal women. Thirty-two healthy and non-obese postmenopausal women without hormone therapy were randomly assigned to exercise + placebo (PLA; n = 15) or exercise + isoflavone supplementation (ISO; n = 17) groups. They performed 30 sessions of combined exercises (aerobic plus resistance) over ten weeks and consumed 100 mg of isoflavone supplementation or placebo. Blood samples were collected after an overnight fast to analyze the lipid profile, interleukin-6 (IL-6), interleukin-8 (IL-8), superoxide dismutase (SOD), total antioxidant capacity (FRAP), and thiobarbituric acid reactive substances (TBARS), before and after ten weeks of the intervention. There were no differences in the changes (pre vs. post) between groups for any of the inflammatory markers, oxidative stress markers or lipid profile variables. However, interleukin-8 was different between pre- and post-tests (p < 0.001) in both groups (&Delta; = 7.61 and 5.61 pg/mL) as were cholesterol levels (p < 0.05), with no interaction between groups. The combination of isoflavone supplementation and exercise training did not alter oxidative stress markers in postmenopausal women, but exercise training alone may increase IL-8 and decrease total cholesterol levels.

Reducing Breast Cancer Recurrence: The Role of Dietary Polyphenolics

Evidence from numerous observational and clinical studies suggest that polyphenolic phytochemicals such as phenolic acids in olive oil, flavonols in tea, chocolate and grapes, and isoflavones in soy products reduce the risk of breast cancer. A dietary food pattern naturally rich in polyphenols is the Mediterranean diet and evidence suggests those of Mediterranean descent have a lower breast cancer incidence. Whilst dietary polyphenols have been the subject of breast cancer risk-reduction, this review will focus on the clinical effects of polyphenols on reducing recurrence. Overall, we recommend breast cancer patients consume a diet naturally high in flavonol polyphenols including tea, vegetables (onion, broccoli), and fruit (apples, citrus). At least five servings of vegetables and fruit daily appear protective. Moderate soy protein consumption (5-10 g daily) and the Mediterranean dietary pattern show the most promise for breast cancer patients. In this review, we present an overview of clinical trials on supplementary polyphenols of dietary patterns rich in polyphenols on breast cancer recurrence, mechanistic data, and novel delivery systems currently being researched.

The effects of dietary soybean isoflavones on growth, innate immune responses, hepatic antioxidant abilities and disease resistance of juvenile golden pompano Trachinotus ovatus

The present study was conducted to investigate the effects of dietary soybean isoflavones (SI) supplementation on growth performance, innate immune responses, hepatic antioxidant abilities, heat shock protein 70 (HSP70) gene expression and resistance to the pathogen Vibrio harveyi in Trachinotus ovatus. A basal diet was supplemented with SI at 0, 10, 20, 40, 60, 80 mg kg(-1) feed for 8 weeks. Significantly maximum weight gain (WG) and specific growth rate (SGR) were observed in treatment with 40 mg kg(-1) SI supplement (P < 0.05). Feed conversion ratio (FCR), feeding rate (FR) and survival rate were not significantly different among treatments. Fish fed a diet with 40 mg kg(-1) SI showed significant increase in plasma total protein content, complement 3 content, lysozyme activity as well as respiratory burst activity, but decrease in alanine aminotransferase and aspartate aminotransferase activities (P < 0.05). Increased plasma alkaline phosphatase activity, hepatic total antioxidative capacity, catalase activity and superoxide dismutase activity were also noticed in fish fed SI at 40 or 60 mg kg(-1) (P < 0.05). On the contrary, the lowest hepatic malondialdehyde (MDA) content was observed in fish fed SI at 40 mg kg(-1) (P < 0.05). Compared with the control, the relative level of HSP70 mRNA in fish fed SI at 40-80 mg kg(-1) were significantly increased, respectively (P < 0.05). After challenge with V. harveyi, significant higher post-challenge survival was observed in fish fed diets with 40-80 mg kg(-1) SI supplement than that in control group (P < 0.05). These results indicated that dietary intake containing SI could enhance the immune ability of fish and improve its resistance to infection by V. harveyi. Especially supplementation with 40 mg kg(-1) SI to the fish for 8 weeks showed remarkable improvement in the growth, non-specific immune responses, hepatic antioxidant abilities and HSP70 gene expression.

Soy, red clover, and isoflavones and breast cancer: a systematic review

BACKGROUND

Soy and red clover isoflavones are controversial due to purported estrogenic activity and possible effects on breast cancer. We conducted a systematic review of soy and red clover for efficacy in improving menopausal symptoms in women with breast cancer, and for potential impact on risk of breast cancer incidence or recurrence.

METHODS

We searched MEDLINE, Embase, the Cochrane Library, and AMED from inception to March 2013 for human interventional or observational data pertaining to the safety and efficacy of soy and red clover isoflavones in patients with or at risk of breast cancer.

RESULTS

Of 4179 records, we included a total of 131 articles: 40 RCTs, 11 uncontrolled trials, and 80 observational studies. Five RCTs reported on the efficacy of soy for hot flashes, showing no significant reductions in hot flashes compared to placebo. There is lack of evidence showing harm from use of soy with respect to risk of breast cancer or recurrence, based on long term observational data. Soy intake consistent with that of a traditional Japanese diet (2-3 servings daily, containing 25-50mg isoflavones) may be protective against breast cancer and recurrence. Human trials show that soy does not increase circulating estradiol or affect estrogen-responsive target tissues. Prospective data of soy use in women taking tamoxifen does not indicate increased risk of recurrence. Evidence on red clover is limited, however existing studies suggest that it may not possess breast cancer-promoting effects.

CONCLUSION

Soy consumption may be associated with reduced risk of breast cancer incidence, recurrence, and mortality. Soy does not have estrogenic effects in humans. Soy intake consistent with a traditional Japanese diet appears safe for breast cancer survivors. While there is no clear evidence of harm, better evidence confirming safety is required before use of high dose (≥ 100 mg) isoflavones can be recommended for breast cancer patients.

Isoflavones inhibit the clonogenicity of human colon cancer cells

Isoflavones are a class of polyphenols that contain various substituents such as hydroxy, methoxy, and glycosyl groups. Methoxy groups are known to increase cell permeability and stability, but small structural changes can result in large differences in biological activity. In this study, the anticancer activities of several methoxy isoflavones were tested using a clonogenic survival assay. The relationship between structural properties of methoxy isoflavones and their anticancer activities on HCT116 colon cancer cell lines were studied quantitatively using comparative molecular field analysis and comparative molecular similarity indices analysis. The purpose of this study was to identify structural changes in isoflavones that increase the inhibitory effect on HCT116 colon cancer cell clonogenicity.

Acute reduction of serum 8-iso-PGF2-alpha and advanced oxidation protein products in vivo by a polyphenol-rich beverage; a pilot clinical study with phytochemical and in vitro antioxidant characterization

Background

Measuring the effects of the acute intake of natural products on human biomarker concentrations, such as those related to oxidation and inflammation, can be an advantageous strategy for early clinical research on an ingredient or product.

Methods

31 total healthy subjects were randomized in a double-blinded, placebo-controlled, acute pilot study with post-hoc subgroup analysis on 20 of the subjects. The study examined the effects of a single dose of a polyphenol-rich beverage (PRB), commercially marketed as "SoZo^®", on serum anti-inflammatory and antioxidant markers. In addition, phytochemical analyses of PRB, and in vitro antioxidant capacity were also performed.

Results

At 1 hour post-intake, serum values for 8-iso-PGF2-alpha and advanced oxidation protein products decreased significantly by 40% and 39%, respectively. Additionally, there was a trend toward decreased C-reactive protein, and increased nitric oxide levels. Both placebo and PRB treatment resulted in statistically significant increases in hydroxyl radical antioxidant capacity (HORAC) compared to baseline; PRB showed a higher percent change (55-75% versus 23-74% in placebo group), but the two groups did not differ significantly from each other.

Conclusions

PRB produced statistically significant changes in several blood biomarkers related to antioxidant/anti-inflammatory effects. Future studies are justified to verify results and test for cumulative effects of repeated intakes of PRB. The study demonstrates the potential utility of acute biomarker measurements for evaluating antioxidant/anti-inflammatory effects of natural products.

No association between SOD2 Val16Ala polymorphism and breast cancer susceptibility: a meta-analysis based on 9,710 cases and 11,041 controls

Breast cancer is the most common cancer in women worldwide, but its etiology is still unclear. It is believed that oxidative stress plays an essential role in the development of breast cancer, while SOD2 is one of the primary enzymes that directly convert potential harmful oxidizing species to harmless metabolites. The association of SOD2 Val16Ala polymorphism and breast cancer risk has been widely reported, but results of previous studies were somewhat contradictory and underpowered. To overcome the limitations of individual study and to understand the real situation, we conducted a systematic review and meta-analysis toward the association between SOD2 Val16Ala polymorphism and breast cancer. Through retrieving MEDLINE, PubMed, Embase, and Web of Science, a total of 17 studies with 9,710 cases and 11,041 controls were identified. The results showed that no significant associations were found for the allele contrast (allele Ala vs. allele Val: OR = 1.020, 95% CI = 0.979-1.062), additive genetic model (Ala/Ala vs. Val/Val: OR = 1.091, 95% CI = 0.969-1.229), dominant genetic model (Ala/Ala +Ala/Val vs. Val/Val: OR = 1.045, 95% CI = 0.961-1.136), and recessive genetic model (Ala/Ala vs. Val/Val +Ala/Val: OR = 1.027, 95% CI = 0.956-1.102). In the stratified analysis by ethnicity and menopausal status, significant associations were also not detected in all genetic models. Conclusively, this meta-analysis strongly suggests that SOD2 Val16Ala polymorphism is not associated with breast cancer susceptibility.

Acute fish oil and soy isoflavone supplementation increase postprandial serum (n-3) polyunsaturated fatty acids and isoflavones but do not affect triacylglycerols or biomarkers of oxidative stress in overweight and obese hypertriglyceridemic men

Chronic consumption of fish and fish oil high in (n-3) PUFA reduces triacylglycerols (TG) but may increase oxidative stress, whereas consumption of soy isoflavones may reduce oxidative stress. Elevated serum TG and oxidative stress are considered cardiovascular disease (CVD) risk factors, but the effects of acute (n-3) PUFA and soy isoflavones on these CVD risk factors are unknown. The purpose of the study was to determine the effects of acutely supplementing a high-fat, high-fructose meal with fish oil and isoflavone placebo (FO) and fish oil placebo and soy isoflavones (ISO). In a randomized, double-blind, placebo-controlled, crossover study, 10 overweight or obese men consumed a high-fat, high-fructose meal with 4 dietary supplement combinations: fish oil placebo and isoflavone placebo (placebo); fish oil and isoflavone placebo (FO); fish oil placebo and isoflavones (ISO); and fish oil and isoflavones (FO + ISO). Serum collected at baseline and at 2, 4, and 6 h postprandially was analyzed for fatty acids, isoflavones, TG, and oxidative stress biomarkers (lipid hydroperoxides, oxidized-LDL, total antioxidant status). FO significantly increased serum (n-3) PUFA and ISO increased serum isoflavones. The study meal significantly increased serum total fatty acids and TG without affecting oxidative stress biomarkers. Serum TG and oxidative stress biomarkers did not differ between treatments. The FO and ISO were bioavailable but did not attenuate the postprandial rise in serum TG. Neither the study meal nor the FO or ISO induced significant changes in oxidative stress biomarkers. The current study adds to a limited literature on the acute effects of FO and ISO interventions on postprandial biomarkers of CVD risk.

Use of conventional and -omics based methods for health claims of dietary antioxidants: a critical overview

This article describes the principles and limitations of methods used to investigate reactive oxygen species (ROS) protective properties of dietary constituents and is aimed at providing a better understanding of the requirements for science based health claims of antioxidant (AO) effects of foods. A number of currently used biochemical measurements aimed of determining the total antioxidant capacity and oxidised lipids and proteins are carried out under unphysiological conditions and are prone to artefact formation. Probably the most reliable approaches are measurements of isoprostanes as a parameter of lipid peroxidation and determination of oxidative DNA damage. Also the design of the experimental models has a strong impact on the reliability of AO studies: the common strategy is the identification of AO by in vitro screening with cell lines. This approach is based on the assumption that protection towards ROS is due to scavenging, but recent findings indicate that activation of transcription factors which regulate genes involved in antioxidant defence plays a key role in the mode of action of AO. These processes are not adequately represented in cell lines. Another shortcoming of in vitro experiments is that AO are metabolised in vivo and that most cell lines are lacking enzymes which catalyse these reactions. Compounds with large molecular configurations (chlorophylls, anthocyans and polyphenolics) are potent AO in vitro, but weak or no effects were observed in animal/human studies with realistic doses as they are poorly absorbed. The development of -omics approaches will improve the scientific basis for health claims. The evaluation of results from microarray and proteomics studies shows that it is not possible to establish a general signature of alterations of transcription and protein patterns by AO. However, it was shown that alterations of gene expression and protein levels caused by experimentally induced oxidative stress and ROS related diseases can be normalised by dietary AO.

Isoflavones and the prevention of breast and prostate cancer: new perspectives opened by nutrigenomics

Epidemiological evidence together with preclinical data from animal and in vitro studies strongly support a correlation between soy isoflavone consumption and protection towards breast and prostate cancers. The biological processes modulated by isoflavones, and especially by genistein, have been extensively studied, yet without leading to a clear understanding of the cellular and molecular mechanisms of action involved. This review discusses the existing gaps in our knowledge and evaluates the potential of the new nutrigenomic approaches to improve the study of the molecular effects of isoflavones. Several issues need to be taken into account for the proper interpretation of the results already published for isoflavones. Too often knowledge on isoflavone bioavailability is not taken into account; supra-physiological doses are frequently used. Characterization of the individual variability as defined by the gut microflora composition and gene polymorphisms may also help to explain the discrepancies observed so far in the clinical studies. Finally, the complex inter-relations existing between tissues and cell types as well as cross-talks between metabolic and signalling pathways have been insufficiently considered. By appraising critically the abundant literature with these considerations in mind, the mechanisms of action that are the more likely to play a role in the preventive effects of isoflavones towards breast and prostate cancers are reviewed. Furthermore, the new perspectives opened by the use of genetic, transcriptomic, proteomic and metabolomic approaches are highlighted.

Effects of fermentation on the phytochemical composition and antioxidant properties of soy germ

Soy germ is a remarkable source of bioactive phytochemicals offering an interesting alternative as starting ingredient for fermented food. This work aimed to determine whether lactic acid bacteria fermentation of soy germ induces changes on its phytochemical composition. The antioxidant properties of fermented soy germ samples periodically taken during the fermentation process were evaluated and correlated with the concentration and structural modifications of isoflavones, saponins, phytosterols and tocopherols. Fermented soy germ extracts exhibited a higher inhibition effect against the superoxide anion radical, and lesser but significant ferric-reducing and DPPH radical scavenging effects compared with raw soy germ. By comparison to the traditional whole seed-based products, soy germ exhibits higher levels of isoflavones, saponins, phytosterols and tocopherols. All these phytochemicals contributed to the antioxidant capacity of soy germ and were conserved under lactic acid bacteria fermentation.

Safety and antioxidant effects of a modest soy protein intervention in hemodialysis patients

Antioxidant/anti-inflammatory effects of isoflavone-containing soy protein could partly explain why hemodialysis patients in Japan tend to outlive U.S. hemodialysis patients. However, a safety concern is that dialysis patients do not clear isoflavones well. A low-dose intervention with high isoflavone soy protein (25 g protein, four times a week for 4 weeks) was tested in 17 U.S. hemodialysis patients (eight given soy protein, nine given whey protein as a control). Soy protein intake produced no harmful effects based on a typical battery of blood safety tests. Post-treatment isoflavone levels, though high, were similar to those reported after a single 20-g soy protein intake by dialysis patients. In addition, intake of soy, but not whey, reduced plasma values for oxidized low-density lipoprotein, a risk factor for cardiovascular disease, which is a common mortality cause in hemodialysis patients. Three other measures of oxidant stress and/or inflammation were unchanged by the modest high isoflavone soy protein intervention. In conclusion, in hemodialysis patients, a fairly short, low intake level intervention with high isoflavone soy protein produced no obvious harm, and produced one potentially beneficial effect. This justifies tests of higher-dose, longer interventions with soy protein in hemodialysis patients.

Meta-Analysis of Soy Intake and Breast Cancer Risk

BACKGROUND

High intake of soy foods has been proposed to contribute to the low breast cancer risk in Asian countries. However, results of epidemiologic studies of this association are highly variable, and experimental data suggest that soy constituents can be estrogenic and potentially risk enhancing. Thus, rigorous evaluation of available epidemiologic data is necessary before appropriate recommendations can be made, especially for women at high risk of breast cancer or those who have survived the disease.

METHODS

We performed a meta-analysis of 18 epidemiologic studies (12 case-control and six cohort or nested case-control) published from 1978 through 2004 that examined soy exposure and breast cancer risk. Pooled relative risk estimates were based on either the original soy exposure measure defined in each study or on an estimate of daily soy protein intake.

RESULTS

Risk estimates, levels and measures of soy exposure, and control for confounding factors varied considerably across studies. In a pooled analysis, among all women, high soy intake was modestly associated with reduced breast cancer risk (odds ratio [OR] = 0.86, 95% confidence interval [CI] = 0.75 to 0.99); the association was not statistically significant among women in Asian countries (OR = 0.89, 95% CI = 0.71 to 1.12). Among the 10 studies that stratified by menopausal status the inverse association between soy exposure and breast cancer risk was somewhat stronger in premenopausal women (OR = 0.70, 95% CI = 0.58 to 0.85) than in postmenopausal women (OR = 0.77, 95% CI = 0.60 to 0.98); however, eight studies did not provide menopause-specific results, six of which did not support an association. When exposure was analyzed by soy protein intake in grams per day, a statistically significant association with breast cancer risk was seen only among premenopausal women (OR = 0.94, 95% CI = 0.92 to 0.97).

CONCLUSIONS

Soy intake may be associated with a small reduction in breast cancer risk. However, this result should be interpreted with caution due to potential exposure misclassification, confounding, and lack of a dose response. Given these caveats and results of some experimental studies that suggest adverse effects from soy constituents, recommendations for high-dose isoflavone supplementation to prevent breast cancer or prevent its recurrence are premature.

Dietary polyphenolic phytochemicals—promising cancer chemopreventive agents in humans? A review of their clinical properties

Epidemiological and preclinical evidence suggests that polyphenolic phytochemicals exemplified by epigallocatechin gallate from tea, curcumin from curry and soya isoflavones possess cancer chemopreventive properties. Whilst such naturally occurring polyphenols have been the subject of numerous mechanistic studies in cells, information on their clinical properties, which might help assess their promise as human cancer chemopreventive agents, is scarce. Therefore, we present a review of pilot studies and trials with a cancer chemoprevention-related rationale, in which either healthy individuals or patients with premalignant conditions or cancer received polyphenolic phytochemicals. The review identifies trial design elements specifically applicable to polyphenolic phytochemicals. The available evidence for tea polyphenols tentatively supports their advancement into phase III clinical intervention trials aimed at the prevention of progression of prostate intraepithelial neoplasia, leukoplakia or premalignant cervical disease. In the case of curcumin and soya isoflavones more studies in premalignacies seem appropriate to optimise the nature and design of suitable phase III trials. The abundance of flavonoids and related polyphenols in the plant kingdom makes it possible that several hitherto uncharacterised agents with chemopreventive efficacy are still to be identified, which may constitute attractive alternatives to currently used chemopreventive drugs.