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.
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Phytoestrogens are mainly excreted in urine, but they have also been found in human and cow’s milk. Previous food analyses have mainly been limited to isoflavones in fruit, vegetables, nuts, and seeds, and there is little data available for lignans and animal foods. In this study, the variability of phytoestrogen content in foods from different sources (e.g., manufacturer or country of origin) as determined. The variability (as a coefficient of variation) is 33% for lignans and 37% for isoflavones. The technique to determine the phytoestrogen content (isoflavones: biochanin A, daidzein, formononetin, genistein, and glycitein; lignans: matairesinol and secoisolariciresinol; enterolignans: enterolignan and enterolactone; coumestrol; and equol) of 115 foods of animal origin and their corresponding vegetarian substitutes. The data show that most animal foods contained phytoestrogens, which would have been derived from animal feeds and pastures, especially those containing clover and other legumes. Although the phytoestrogen content in animal products is low when compared to soy-based foods (e.g., soy milk), the range is similar to that of many commonly consumed vegetables. Eggs (particularly the yolk), cheese, and other milk-derived products contained a high proportion of mammalian phytoestrogens, whereas the phytoestrogens in meat and fish were almost entirely composed of the unmetabolised plant precursors. Soy is used as a food additive, and some of the somewhat higher levels of isoflavones in processed foods, such as ice cream, are indicative of their presence.