Phytoestrogen Content of Foods of Animal Origin: Dairy Products, Eggs, Meat, Fish, and Seafood

Abstract

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 µg/100 g of wet weight (isoflavones, 6 µg/100 g; lignans, 6 µg/100 g; equol, 3 µg/100 g; and enterolignans, 6 µg/100 g). In infant soy formula, 19 221 µg/100 g phytoestrogens were detected (compared to 59 µg/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.

Dietary intakes and food sources of phytoestrogens in the European Prospective Investigation into Cancer and Nutrition (EPIC) 24-hour dietary recall cohort

“…They are also found in much lower concentrations in other plant products 3,4 and even in animal products. 5 Classically, the most studied isoflavones were daidzein, genistein and glycitein. In the last two decades, biochanin A and formononetin have also been considered, because they are converted by the intestinal microbiota into genistein and daidzein, respectively.…”

“…8 As a result of such isoflavone and lignan microbial metabolism in animal gut, these metabolites may also be present in foods of animal origin. 5 However, because their occurrence and biosynthesis are different, some authors classify these enterolignans and equol in separate groups, particularly in epidemiological studies. 4 The bioactivity of phytoestrogens is based mostly on their weak affinity to the estrogen receptor b and to a lesser extent estrogen receptor a.…”

The Soy Isoflavone Equol May Increase Cancer Malignancy via Up-regulation of Eukaryotic Protein Synthesis Initiation Factor eIF4G

“…Isoflavones found primarily in legumes and particularly in soy are a major class of phytoestrogens that are structurally and/or functionally similar to 17␤-estradiol (1). These compounds have received increasing attention for their potential estrogenic or antiestrogenic effects, leading to concerns surrounding the use of phytoestrogen supplements in breast cancer patients who may overexpress estrogen receptors in the tumor tissue (2).…”

Fresh and ensiled forages as a source of estrogenic equol in bovine milk: a review

“…It is produced by various intestinal bacteria from some ingested isoflavones (for a review see Setchell and Clerici (2010)). Dietary equol thus occurs in some foods of mammalian origin, with milk being its important source (Kuhnle et al, 2008).…”