USDA database for the isoflavone content of selected foods. Release 2

Authors: Bhagwat, Seema; Haytowitz, David; Holden, Joanne

Submitted to: Home Page
Publication Type: Other
Publication Acceptance Date: 9/8/2008
Publication Date: 9/8/2008
Citation: Bhagwat, S.A., Haytowitz, D.B., Holden, J.M. 2008. USDA Database for the Isoflavone Content of Selected Foods, Release 2. USDA National Nutrient Database for Standard Reference. Available: http://www.ars.usda.gov/nutrientdata.

Interpretive Summary: Isoflavones, a subclass of flavonoids, have weak estrogenic activities and also other non-hormonal biological properties which may have beneficial health effects. Soy isoflavones alone and along with soy proteins, lower serum total and LDL cholesterol in humans and may lower the risk of cardiovascular diseases. Isoflavones may also reduce the risk of some cancers, particularly, prostate cancer. The first USDA-Iowa State University Isoflavones Database for 128 foods was released in 1999 by the Nutrient Data Laboratory (NDL) of ARS/USDA. With the approval of a health claim for soy proteins from the Food and Drug Administration (FDA) in 1999, the number of new soy products and their consumption has increased, thus increasing the need to update the 1999 database. The NDL reviewed literature published since 1999 in peer-reviewed journals through various database searches and retrieved 265 articles. Sixty-six of these articles contained acceptable analytical data on the three major isoflavones, daidzein, genistein, and glycitein. Data from these articles were evaluated for data quality and then combined with the data from the first release to update the isoflavones database. The updated database now contains values for 550 foods. Two hundred and sixty-eight of these 550 foods did not contain any isoflavones. Therefore they were separated from the main table and a list of these foods is included in the database. It also contains a separate table for 200 selected foods for other plant estrogens: coumestrol, formononetin, and biochanin A. All the values in the tables are reported as mg/100g of fresh weight of the edible portion of the food. The isoflavone values for soybeans and their products vary considerably depending on the variety, crop year, and location. The soybean data, therefore, are presented separately for different countries or regions: Australia, Brazil, China, Europe, Japan, Korea, Taiwan, and the United States. The average for "all sources" of soybeans is also included. The database is available on the NDL web site: http://www.ars.usda.gov/nutrientdata. This database, along with two other databases released by the NDL, flavonoids and proanthocyanidins, will be useful to assess flavonoid intakes when evaluating health benefits in humans.

Technical Abstract: Isoflavones, a subclass of flavonoids, have weak estrogenic, as well as other biological properties that may contribute to the reduction of the risk of some chronic diseases. Consumption of soy isoflavones alone and along with soy protein lowers serum total and LDL cholesterol in humans. A review of clinical trials of soy isoflavones suggests some skeletal benefits in younger postmenopausal women. Although evidence for the beneficial role of isoflavones in breast cancer has become conflicted, results of clinical trials for prostate cancer are encouraging and non-hormonal properties of isoflavones, including cell cycle arrest and cell apoptosis, may reduce the risk of some cancers. The database for the isoflavone content of foods is necessary to assess the effects of the intake of isoflavones on various biological parameters. Since soybeans are a major source of dietary isoflavones and soybeans and soybean products are also a good source of protein, inclusion of soy foods in the diet is recommended. The Nutrient Data Laboratory (NDL) of ARS/USDA, in collaboration with the Iowa State University, released a Special Interest Database on isoflavones in foods in 1999. With the approval of a health claim for soy protein from the Food and Drug Administration (FDA) in 1999, the number of new soy products and their consumption has increased, thus increasing the need to update the 1999 database. Approximately 265 articles published in refereed journals since 1999 were retrieved through literature searches conducted on various databases. Sixty-six articles contained acceptable analytical data for isoflavones in foods and food ingredients and were used for updating the database. Data in all the articles were evaluated for data quality using data quality evaluation system developed by the NDL scientists. All the data were converted into aglycone forms of the three prevalent isoflavones, daidzein, genistein, and glycitein, using appropriate molecular weights. These data were merged with the earlier data (1999) to update the database. The mean, standard error, minimum, and maximum values for aglycone forms of isoflavones are reported as mg/100g of fresh weight of edible portion of food. The updated database contains values for daidzein, genistein, and glycitein for 282 foods and food ingredients along with the data quality indicator (Confidence Code, CC) and data sources (references used). Two hundred and sixty-eight foods and ingredients for which zero values were reported for all three isoflavones are presented in a separate list, thus the database provides information on a total of 550 foods. The previous release contained values for 128 foods. Values for three other phytoestrogens---coumestrol, formononetin, and biochanin A---for approximately 200 foods are also reported in a separate table as mg/100g fresh weight of edible portion. The variety, the crop year, and the location affect the isoflavone content of the soybeans and contribute to the large variability in the isoflavone content of soybeans as well as soy foods. The soybean data, therefore, are presented separately for different countries or regions: Australia, Brazil, China, Europe, Japan, Korea, Taiwan, and the United States. The generic mean for "all sources" of soybeans is also included. The documentation explaining the method and procedure for preparing the table and the reference list for the sources of the data are included. The database is available on the NDL web site: http://www.ars.usda.gov/nutrientdata. This database complements the other two databases for flavonoid compounds, "USDA Database for the Flavonoid Content of Selected Foods" and "USDA Database for the Proanthocyanidin Content of Selected Foods" released by the NDL.