Isoflavone Content of Foods and Supplements

Supplements

Setchell KD, Brown NM, Desai P, et al. Bioavailability of pure isoflavones in healthy humans and analysis of commercial soy isoflavone supplements.
J Nutr 2001;131:1362S-75S.

The pharmacokinetic behavior of naturally occurring isoflavones has been determined for the first time in healthy adults. We compared plasma kinetics of pure daidzein, genistein and their beta-glycosides administered as a single-bolus dose to 19 healthy women. This study demonstrates differences in the pharmacokinetics of isoflavone glycosides compared with their respective beta-glycosides. Although all isoflavones are efficiently absorbed from the intestinal tract, there are striking differences in the fate of aglycones and beta-glycosides. Mean time to attain peak plasma concentrations (t(max)) for the aglycones genistein and daidzein was 5.2 and 6.6 h, respectively, whereas for the corresponding beta-glycosides, the t(max) was delayed to 9.3 and 9.0 h, respectively, consistent with the residence time needed for hydrolytic cleavage of the glycoside moiety for bioavailability. The apparent volume of distribution of isoflavones confirms extensive tissue distribution after absorption. Plasma genistein concentrations are consistently higher than daidzein when equal amounts of the two isoflavones are administered, and this is accounted for by the more extensive distribution of daidzein (236 L) compared with genistein (161 L). The systemic bioavailability of genistein [mean AUC = 4.54 ?g/(mL. h)] is much greater than that of daidzein [mean AUC = 2.94 ?g/(mL. h)], and bioavailability of these isoflavones is greater when ingested as beta-glycosides rather than aglycones as measured from the area under the curve of the plasma appearance and disappearance concentrations. The pharmacokinetics of methoxylated isoflavones show distinct differences depending on the position of the methoxyl group in the molecule. Glycitin, found in two phytoestrogen supplements, underwent hydrolysis of the beta-glycoside moiety and little further biotransformation, leading to high plasma glycitein concentrations. Biochanin A and formononetin, two isoflavones found in one phytoestrogen supplement, were rapidly and efficiently demethylated, resulting in high plasma genistein and daidzein concentrations typically observed after the ingestion of soy-containing foods. These differences in pharmacokinetics and metabolism have implications for clinical studies because it cannot be assumed that all isoflavones are comparable in their pharmacokinetics and bioavailability. An analysis of 33 phytoestrogen supplements and extracts revealed considerable differences in the isoflavone content from that claimed by the manufacturers. Plasma concentrations of isoflavones show marked qualitative and quantitative differences depending on the type of supplement ingested. These studies indicate a need for improvement in quality assurance and standardization of such products.


Nurmi T, Mazur W, Heinonen S, Kokkonen J, Adlercreutz H. Isoflavone content of the soy based supplements. J Pharm Biomed Anal 2002;28:1-11.

A large number of soy isoflavone products with indications of possible health effects are available on the market. Fifteen different soy based products were analyzed using high performance liquid chromatography (HPLC) with coulometric electrode array detector to determine the total amount of isoflavones in aglycones after the hydrolysis and identify the different forms of the isoflavone conjugates. The aim of the study was to evaluate how well the isoflavone content data supplied by the producers correspond to our analysis results. Only one product contained isoflavones measured in aglycones the same amount as was the value given by the producer. The total amount of the isoflavones in aglycones ranged from 0.121 to 201 mg/g. Measured amounts of isoflavones in aglycones after the hydrolysis were in general lower than the values in the product labels. Product data were often confusing and the concrete amount of isoflavones was difficult to find out.


Howes JB, Howes LG. Content of isoflavone-containing preparations. Med J Aust 2002;176:135-6.

Lin J, Padmanaban PG, Wang C. Retention of isoflavones and saponins during the processing of soy protein isolates. J Am Oil Chemists Soc 2006;83:59-63.

ABSTRACT: The mass balance of saponins during processing of soy protein isolates (SPI) was established, and the effects of precipitating and washing (P/W) temperatures (0, 10, 25, 40, and 50°C) on the retention of isoflavones and saponins were investigated in this study. About 41% of total saponins in soy flour (SF) were found to remain in SPI during processing, whereas 42% remained unextracted in the solid waste. None was detected in the whey or wash water. The study also revealed that only about 27% of total isoflavones from SF remained in the final SPI when P/W was performed at 50°C. As much as 40% of the total isoflavones could be retained in SPI when P/W was conducted at 25, 10, or 0°C. When the P/W temperature was 50°C, the percentages of total isoflavones lost during extraction, precipitation, and washing were 28, 22, and 6%, respectively. When the temperature was changed to 0°C, the percentages of isoflavones lost during extraction, precipitation, and washing were 28, 11, and 5%, respectively. The P/W temperatures did not affect the distribution of saponins in different streams during the processing of SPI. Lowering the P/W temperature did not significantly lower the protein content in SPI unless the temperature was reduced to 0°C. Paper no. J11002 in JAOCS 83, 59–63 (January 2006).


Prabhakaran MP, Hui LS, Perera CO. Evaluation of the composition and concentration of isoflavones in soy based supplements, health products and infant formulas. Food Res Inter 2006;39:730–8.

Isoflavones are weak estrogenic compounds found in soybeans and soy foods. The objective of the present study was to determine the content and composition of isoflavones in different soy isoflavone supplements, soy based health products and infant formulas. Commercially available samples of 13 different soy supplements and 11 soy based health products obtained from South East Asia were analyzed for their isoflavone concentrations by using high-performance liquid chromatography and their peak identities confirmed by LC–MS. The extent of daily intake of isoflavones from different products based on the directions for their consumption was further evaluated. The amount of isoflavones in dietary supplements, soy based health products and infant formulas ranged from 405 to 57,570, 46.32–1333.80 and 59.54–226.84 lg/g of the sample, respectively, expressed as aglycone equivalents. 2006 Elsevier Ltd. All rights reserved.


Thompson LU, Boucher BA, Cotterchio M, Kreiger N, Liu Z. Dietary phytoestrogens, including isoflavones, lignans, and coumestrol, in nonvitamin, nonmineral supplements commonly consumed by women in Canada. Nutr Cancer 2007;59:176-84.

Twenty-one nonvitamin, nonmineral dietary supplements commonly consumed by women in Canada were analyzed for isoflavones (formononetin, daidzein, genistein, glycitein), lignans (pinoresinol, lariciresinol, secoisolariciresinol, matairesinol), and coumestrol to complement our previously published food phytoestrogen database. Supplements containing soy or red clover had the highest concentrations of total isoflavones (728.2-35,417.0 ug/g) and total phytoestrogens (1030.1-35,517.7 ug/g) followed by licorice and licorice-containing supplements (41.3-363.3 ug/g isoflavones; 56.5-370.0 ug/g total phytoestrogens). Other supplements had considerably less isoflavones (</= 19.0 ug/g) and total phytoestrogens (</= 44.2 ug/g). Lignans were present in all (</= 298.9 ug/g), whereas coumestrol was either not present or present in only small amounts (</= 3.0 ug/g). Supplements differed in phytoestrogen profiles. The daily intake of isoflavones and lignans from some supplements may greatly exceed those from several servings of soy or vegetables. Hence, the intake of supplements should be taken into consideration in clinical or epidemiological studies for more accurate estimation of phytoestrogen intakes.


Clarke DB, Bailey V, Lloyd AS. Determination of phytoestrogens in dietary supplements by LC-MS/MS. Food additives & contaminants Part A, Chemistry, analysis, control, exposure & risk assessment 2008;25:534-47.

Labelling data quantifying the exact content of individual phytoestrogen analytes in dietary supplements are generally poor. As these products are commonly used in the management of menopause symptoms, any clinical benefits would be dependent on the exact dosage of isoflavones received. Well-established extraction procedures and updated isotope dilution mass spectrometry liquid chromatography coupled with tandem mass spectrometry detection (LC-MS/MS) have been used to accurately quantify the concentrations of ten common isoflavones in 35 dietary supplement samples on sale in the UK, Canada and Italy. Concentration-specific ionization suppression is described for biochanin A and formononetin. All supplements contained phytoestrogens. The soya isoflavones (genistein, daidzein, glycitein) were present in all products and the majority also contained the red clover isoflavones (biochanin A, formononetin) and some the Kudzu isoflavones (daidzein, puerarin). The content of total isoflavones per dose ranged from <1 to 53 mg. Trace amounts of coumestrol were found in six products. Other less common analytes, the prenylnaringenins (6-prenylnaringenin, 8-prenylnaringenin, 6,8-diprenylnaringenin) were not found in any of the products. Only 14 of 35 supplements were found to deliver more than or equal to 40 mg day(-1) of aglycone isoflavones, a consensus dose value recognized as delivering therapeutic benefit. Eleven did not match label claims. Six delivered less than 10 mg day (-1) of isoflavones. There has been little improvement in the overall quality of industry labelling in the five years since this was last investigated. Consequently, the public, retailers and healthcare professionals should consider using standardized isoflavone supplements, which are supported by analytical measurements.


Concetta Boniglia, Brunella Carratù, Raffaella Gargiulo, Stefania Giammarioli, Maurizio Mosca, Elisabetta Sanzini. Content of phytoestrogens in soy-based dietary supplements. Food Chemistry 115 (2009) 1389–1392

The isoflavone content of 14 soy-based dietary supplements intended to help alleviate perimenopausal and menopausal symptoms on sale in Italy were analysed using HPLC with UV detection. The aim was to quantify soy isoflavones after hydrolysis as aglycones, which are the bioactive part of isoflavone molecules. In the examined products, the amounts of isoflavones were frequently expressed ambiguously, and none of the products stated whether the isoflavone content of the product was expressed as aglycones or as conjugates. Each product revealed a different aglycone concentration profile. These supplements have different ‘‘fingerprints”, probably due to different sources of raw materials and to methods used in processing and preparation of extracts. In more than half the supplements tested, the actual values contained were below those stated and below those expected to help alleviate perimenopausal and menopausal symptoms.


Reiter E, Beck V, Medjakovic S, Mueller M, Jungbauer A. Comparison of hormonal activity of isoflavone-containing supplements used to treat menopausal complaints. Menopause 2009;16:1049-60.

OBJECTIVES: The isoflavones present in red clover and soy are used as an alternative treatment for menopausal complaints and are commercially available as high-dose food supplements. These preparations contain varying amounts of active ingredients, often without detailed specifications. Thus, it is difficult to derive a recommended daily dose, and the reliability of these products is rather low. METHODS: We quantified the isoflavone content of 19 different isoflavone-containing preparations and compared their binding and transactivational activities with regard to estrogen receptor alpha, estrogen receptor beta, androgen receptor, progesterone receptor, peroxisome-proliferator-activated receptor, and aryl hydrocarbon receptor. RESULTS: The food supplements that we tested bound to and transactivated both the estrogen receptors and the other receptors. After comparing the isoflavone content quantified by us with the isoflavone content specified on the package labels, we found that at least the specified isoflavone content or more could be detected in only 5 of the 19 food supplements that we tested. CONCLUSIONS: Preparations containing isoflavones should be standardized for the isoflavone aglycone content to facilitate the prediction of theoretical hormonal activity, facilitate the intake of a controlled amount of isoflavones, and ensure greater product reliability.


Fiechter G, Raba B, Jungmayr A, Mayer HK. Characterization of isoflavone composition in soy-based nutritional supplements via ultra performance liquid chromatography. Anal Chim Acta 2010;672:72-8.
The specific isoflavone composition of nutritional supplements is commonly not-labeled, although the stated amounts are strongly dependent on the present isoflavone conjugates. Hence, 11 soy-based dietary supplements were characterized via a newly established ultra performance liquid chromatography (UPLC) method, on both their native conjugated isoflavone spectra, as well as on quantitative amounts derived as total aglycones after enzymatic hydrolysis utilizing Helix pomatia juice. Capitalizing on sub-2 microm particles, the established RP-UPLC technique facilitated efficient chromatographic separation of all 12 soy intrinsic isoflavone forms within 10 min. Derived native isoflavone profiles implied a certain variability, comprising conjugated forms, especially glycosides, as the predominant isoflavonic constituents throughout the majority of supplements, whereas only two samples indicated the more bioavailable free aglycones as prevailing compounds. Moreover, the robust quantification as total aglycones subsequent to enzymatic hydrolysis, unexceptionally yielded negative deviations referring to the labeled specifications, thus implying that stated amounts were typically calculated on basis of the high molecular isoflavone conjugates. Thus, especially in regard to better comparability, regulations concerning an uniform labeling basis are needed.


Yanaka K, Takebayashi J, Matsumoto T, Ishimi Y. Determination of 15 isoflavone isomers in soy foods and supplements by high-performance liquid chromatography. J Agric Food Chem 2012;60:4012-6.

Soy isoflavone is the generic name for the isoflavones found in soy. We determined the concentrations of 15 soy isoflavone species, including 3 succinyl glucosides, in 22 soy foods and isoflavone supplements by high-performance liquid chromatography (HPLC). The total isoflavone contents in 14 soy foods and 8 supplements ranged from 45 to 735 mug/g and from 1,304 to 90,224 mug/g, respectively. Higher amounts of succinyl glucosides were detected in natto, a typical fermented soy product in Japan; these ranged from 30 to 80 mug/g and comprised 4.1-10.9% of the total isoflavone content. In soy powder, 59 mug/g of succinyl glucosides were detected, equivalent to 4.6% of the total isoflavone content. These data suggest that the total isoflavone contents may be underestimated in the previous studies that have not included succinyl glucosides, especially for Bacillus subtilis -fermented soy food products.

Foods/Beverages

Murphy PA, Song T, Buseman G, et al. Isoflavones in retail and institutional soy foods. J Agric Food Chem 1999;47:2697-704.

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.


Murphy PA, Barua K, Hauck CC. Solvent extraction selection in the determination of isoflavones in soy foods. J Chromatogr B Analyt Technol Biomed Life Sci 2002;777:129-38.

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



Kuhnle GG, Dell’Aquila C, Aspinall SM, Runswick SA, Mulligan AA, Bingham SA. Phytoestrogen content of beverages, nuts, seeds, and oils. J Agric Food Chem 2008;56:7311-5.

Phytoestrogens are secondary plant metabolites that have received increasing attention for their bioactivity, in particular due to their structural and functional similarity to 17beta-estradiol. Although urinary and plasma phytoestrogens can be used as biomarkers for dietary intake, this is often not possible in large epidemiological studies or in the assessment of general exposure in free-living individuals. Accurate information about dietary phytoestrogens is therefore important, but there are very limited data concerning food contents. In this study was analyzed a comprehensive selection of tea, coffee, alcoholic beverages, nuts, seeds, and oils for their phytoestrogen content using a newly developed sensitive method based on LC-MS incorporating (13)C 3-labeled standards. Phytoestrogens were detected in all foods analyzed, although the contents in gin and bitter (beer) were below the limit of quantification (1.5 microg/100 g). Lignans were the main type of phytoestrogens detected. Tea and coffee contained up to 20 microg/100 g phytoestrogens and beer (except bitter) contained up to 71 microg/100 g, mainly lignans. As these beverages are commonly consumed, they are a main source of dietary lignans. The results published here will contribute to databases of dietary phytoestrogen content and allow a more accurate determination of phytoestrogen exposure in free-living individuals.


Kuhnle GG, Dell’Aquila C, Aspinall SM, Runswick SA, Mulligan AA, Bingham SA. Phytoestrogen content of foods of animal origin: dairy products, eggs, meat, fish, and seafood. J Agric Food Chem 2008;56:10099-104.

Dietary phytoestrogens may be involved in the occurrence of chronic diseases. Reliable information on the phytoestrogen content in foods is required to assess dietary exposure and disease risk in epidemiological studies. However, existing analyses have focused on only one class of these compounds in plant-based foods, and there is only little information on foods of animal origin, leading to an underestimation of intake. This is the first comprehensive study of phytoestrogen content in animal food. We have determined the phytoestrogen content (isoflavones: biochanin A, daidzein, formononetin, genistein, and glycitein; lignans: secoisolariciresinol and matairesinol; coumestrol; equol; enterolactone; and enterodiol) in 115 foods of animal origin (including milk and milk-products, eggs, meat, fish, and seafood) and vegetarian substitutes using liquid chromatography-mass spectrometry (LC-MS) with (13)C-labeled internal standards. Phytoestrogens were detected in all foods analyzed; the average content was 20 microg/100 g of wet weight (isoflavones, 6 microg/100 g; lignans, 6 microg/100 g; equol, 3 microg/100 g; and enterolignans, 6 microg/100 g). In infant soy formula, 19 221 microg/100 g phytoestrogens were detected (compared to 59 microg/100 g in non-soy formula). Our study shows that all foods analyzed contained phytoestrogens and most foods (except for fish, seafood, and butter) contained mammalian phytoestrogens (enterolignans and equol). This is the first comprehensive study of phytoestrogen content of foods of animal origin and will allow for a more accurate estimation of exposure to dietary phytoestrogens.


Whent M, Hao J, Slavin M, et al. Effect of genotype, environment, and their interaction on chemical composition and antioxidant properties of low-linolenic soybeans grown in Maryland. J Agric Food Chem 2009;57:10163-74.

Eight soybean genotypes grown in three environments in Maryland were analyzed for total phenolic content (TPC), antioxidant capacity, isoflavone composition, lutein, tocopherols, fatty acid composition, and oil content. Fatty acid composition, isoflavones, lutein, tocopherols, and specific antioxidant assays had significant variation by genotype (G) (P < 0.05). Environment (E) had a significant effect on fatty acids, lutein, individual tocopherols, oxygen radical absorbance capacity (ORAC), and the isoflavone glycitein (P < 0.05). In addition, the interaction between genotype and environment (G x E) showed a significant effect on antioxidant capacity, isoflavones, lutein, tocopherols, and fatty acids (P < 0.05). Factorial designed analysis of variance of all data indicated that G had a larger effect than E on the majority of fatty acids, total isoflavones, lutein, and total tocopherols. E had a larger effect than G on stearic acid (18:0), glycitein, delta-tocopherol, and ORAC. The results of this study show that the genotype, growing environment, and their interactions in Maryland-grown soybeans may alter the levels of specific health-enhancing properties.


Kuhnle GG, Dell’aquila C, Aspinall SM, Runswick SA, Mulligan AA, Bingham SA. Phytoestrogen content of cereals and cereal-based foods consumed in the UK. Nutr Cancer 2009;61:302-9.

Dietary phytoestrogens may be involved in the occurrence of chronic diseases. Reliable information on the phytoestrogen content in foods is required to assess dietary exposure and disease risk in epidemiological studies. However, there is little information on isoflavone, lignan, and coumestrol content of cereals and cereal-based foods, leading to an underestimation of intake. This is the first study of phytoestrogens (isoflavones: biochanin A, daidzein, formononetin, genistein, glycitein; lignans: matairesinol, secoisplariciresinol; coumestrol) in a comprehensive selection of 101 cereals and cereal-based foods-including breads, breakfast cereals, biscuits, pasta and rice-consumed in the UK using a sensitive LCMS technique with 13C-labelled internal standards. Phytoestrogens were detected in all foods analyzed; bread contained the highest amount of phytoestrogens-many as isoflavones-with an average content of 375 +/- 67 microg/100 g wet weight (excluding soya-linseed bread with 12,000 microg/100 g). Most other foods contained less than 100 microg/100 g, many as lignans. Our study shows that all foods analyzed contained phytoestrogens, with the highest amount found in breads, making them one of the main sources of dietary phytoestrogens in the UK. These results will allow a more accurate estimation of exposure to dietary phytoestrogens.


Yuan JP, Liu YB, Peng J, Wang JH, Liu X. Changes of isoflavone profile in the hypocotyls and cotyledons of soybeans during dry heating and germination. J Agric Food Chem 2009;57:9002-10.

A gradient reversed-phase high-performance liquid chromatography (HPLC) method has been developed to be suitable for the separation and determination of 12 isoflavones in soybeans. Profiles of daidzein, genistein, glycitein, and their malonyl-, acetyl-, and nonconjugated beta-glycosides were determined in cotyledons and hypocotyls of soybeans as affected by dry heating and germination. The results showed that the compositions and concentrations of isoflavones were remarkably different in the two parts of soybeans, and hypocotyls contained a much higher content of isoflavones than cotyledons (e.g., 7.8-fold higher). In hypocotyls, daidzein and its glycoside conjugates (59.6%) were the most abundant isoflavones, being followed by glycitein (26.6%) and genistein series (13.8%). In cotyledons, genistein and its glycoside conjugates (61.9%) were the main isoflavones, being followed by daidzein series (38.1%), and no glycitein series was found. Both hypocotyls and cotyledons contained remarkably high amounts of malonylglycosides (69.1 and 69.4%, respectively) and beta-glycosides (27.1 and 25.4%), and only a very small quantity of aglycones (3.8 and 5.2%) and no acetylglycosides were detected. Acetylglycosides and beta-glycosides were the thermal decarboxylation and deesterification products, respectively, of malonylglycosides, which were thermally unstable. The relative rates of decarboxylation and deesterification reactions were different in cotyledons and hypocotyls at different temperatures. During the process of germination, beta-glycosides decreased, and malonylglycosides and aglycones increased, and then, malonylglycosides were the major fractions in germinating soybeans. Interestingly, the present study occasionally found a significant circadian change between malonylglycosides and aglycones with a nocturnal increase of aglycones and decrease of malonylglycosides during germination, and even aglycones became the most abundant forms at night. However, this mechanism is yet to be investigated.


Chan SG, Murphy PA, Ho SC, et al. Isoflavonoid content of Hong Kong soy foods. J Agric Food Chem 2009;57:5386-90.

Progress in understanding the effects of dietary soy isoflavones on chronic disease prevention in the Hong Kong Chinese population has been hampered by the lack of a comprehensive soy isoflavone database. In this study, we determined the concentrations and distribution of isoflavones in 47 foods included in a soy food frequency questionnaire by reverse-phase HPLC. Results indicated that most soy products contained isoflavones ranging from 1 mg of aglucon equivalents/100 g of wet weight (bean strip noodle and egg bean curd) to 80 mg of aglucon equivalents/100 g of wet weight (oyster sauce soybean and sweet bean curd sheet). Among our food groups, mean isoflavone concentrations were lowest in the soy milk group (9.99 mg of aglucon equivalents/100 g of wet weight) and highest in the bean curd skin group (40 mg of aglucon equivalents/100 g of wet weight). The conjugation patterns of isoflavones varied within and between food groups as influenced by the types of soybeans and the processing or cooking techniques used. The isoflavone concentrations reported herein will be useful for ascertaining the relationship between exposure to dietary soy isoflavones and health effects in the Chinese population.


Yanaka K, Takebayashi J, Matsumoto T, Ishimi Y. Determination of 15 isoflavone isomers in soy foods and supplements by high-performance liquid chromatography. J Agric Food Chem 2012;60:4012-6.

Soy isoflavone is the generic name for the isoflavones found in soy. We determined the concentrations of 15 soy isoflavone species, including 3 succinyl glucosides, in 22 soy foods and isoflavone supplements by high-performance liquid chromatography (HPLC). The total isoflavone contents in 14 soy foods and 8 supplements ranged from 45 to 735 mug/g and from 1,304 to 90,224 mug/g, respectively. Higher amounts of succinyl glucosides were detected in natto, a typical fermented soy product in Japan; these ranged from 30 to 80 mug/g and comprised 4.1-10.9% of the total isoflavone content. In soy powder, 59 mug/g of succinyl glucosides were detected, equivalent to 4.6% of the total isoflavone content. These data suggest that the total isoflavone contents may be underestimated in the previous studies that have not included succinyl glucosides, especially for Bacillus subtilis -fermented soy food products.