What foods are high in estrogen
Plant derived estrogens or phytoestrogens are found in a wide variety of foods, most notably soy 1). Phytoestrogens are present in many human foodstuffs including fruits (plum, pear, apple grape berries, …), vegetables (beans, sprouts, cabbage, spinach, soybeans, grains, hops, garlic, onion,…), wine, tea, and they have been identified in a number of botanical dietary supplements. Phytoestrogens are strikingly similar in chemical structure to the mammalian estrogen, estradiol, and bind to estrogen receptors (ERs) with the preference for ERβ 2). This suggests that these compounds may exert tissue specific effects, beside other non receptor mediated biological activities, as antioxidant capacity and antiproliferative/antiangiogenic effects.
Estrogen Replacement Therapy has many demonstrated benefits, including decreases in bone loss, fractures and tooth loss; decreased risk of myocardial infarction, gastrointestinal cancer and colon cancer; delay of onset of Alzheimer’s disease; and probable decrease in age-related macular degeneration and reversal of urogenital atrophy. Unfortunately, Estrogen Replacement Therapy is also associated with elevated risk of gallstones, deep vein thrombosis and endometrial cancer, and there is growing evidence that Estrogen Replacement Therapy may also be associated with a moderate increase in risk of breast cancer. Even a modest increase in cancer risk may be problematic, since long term Estrogen Replacement Therapy may be required to achieve desired effects such as cardioprotection and prevention of osteoporosis.
Plants vary intra- and inter-species in the types and concentrations of phytoestrogens due to variables in plant growth, soil, weather conditions and the age of plant. Chemically phytoestrogens are phenolic phytochemicals or polyphenols. These are the largest category of phytochemicals and the most widely distributed in the plant kingdom 3). They include a wide variety of structurally different compounds such as isoflavones, mainly found in soy, lignans found in grains, stilbenes found in the skin of grapes. Other less investigated compounds include flavones, flavans, isoflavanes and coumestans. Phytoestrogens are also present in numerous dietary supplements and widely marketed as a natural alternative to estrogen replacement therapy.
Table 1. Main chemical categories of phytoestrogens
| Lignans | Flavonols | Coumestans | Isoflavones | Stilbenes |
|---|---|---|---|---|
| Enterolactone | Quercetin | Cumestrol | Glycitein | Resveratrol |
| Enterodiol | Rutin | Genistein | ||
| Daidzein |
Note: The phytoestrogens classification is controversial, currently phytoestrogens can be subdivided in four main classes: flavonoids (flavones and isoflavones), lignans, coumenstans and stilbenes
[Source 4)]Although in test tube and animal studies provide preliminary plausible mechanisms to explain how phytoestrogens act, the applications of diets rich in such compounds and their consequent biological effects still need to be fully examined, tested and confirmed through traditional scientific experimental pathway.
The question of whether or not phytoestrogens are beneficial or harmful to human health remains unresolved. Unfortunately, due to the great diversity of phytoestrogen compounds, including different bioavailability, pharmacokinetics, pharmacological properties and metabolic fates, it is quite complex to define, assess and understand their precise effects on human health since large and time extended intervention studies are needed. Plus the answer is likely to be complex and may depend on age, health status, and even the presence or absence of specific gut microflora. Clarity on this issue is needed because global consumption is rapidly increasing.
Natural estrogens are involved in a multiplicity of programmed events in target tissues as uterus, breast, pituitary gland and hormone responsive tumors. The initiation of estrogen action by all of the estrogens is considered to be the same in each target tissue. Estrogen firstly bind to the nuclear ER (estrogen receptor), then an estrogenic ligand causes a conformational change that encourages dimerization and interaction with either specific DNA sequences or a protein-protein interaction with AP-1 or Sp1 sites in the promoter region of estrogen-responsive genes 5). These events herald the biological effects of estrogen in the specific target tissue or tumor. A small percentage (2-3%) of estrogen receptors are located on the cell membrane and contribute to non genomic effects of estrogen 6). Two estrogen receptors are currently known, ERα and ERβ. Although the two estrogen receptors can be localized within the same cell, they vary in tissue distributions and can have different effects on mixed agonist and antagonist molecules.
Table 2. Dietary sources of phytoestrogens (foods with estrogen)
| Group | Subgroup | Examples | Dietary sources |
|---|---|---|---|
| 17β-Estradiol | Endogenous Estrogen | N/A | N/A |
| Polyphenols | Resveratrol | Grape skin, red wine | |
| Flavonoids | Flavanones | Eriodictyol, Hesperetin, Homoeriodictyol,Naringenin | Citrus fruits and juices |
| Flavones | Apigenin, Luteolin, Tangeritin | Parsley, celery, capsicum pepper | |
| Flavonols | Fisetin, Kaempferol, Myricetin, Pachypodol, Quercetin, Rhamnazin | Kale, broccoli, onions tomatoes, lettuce, apples, grapes, red wine | |
| Catechins | Proanthocyanides | Chocolate, green tea, beans, apricots, cherries, berries | |
| Isoflavonoids | Isoflavones | Biochanin A, Clycitein, Daidzein, Formononetin, Genistein | Soy beans, and other legumes |
| Isoflavans | Equol | Metabolite of daidzein | |
| Coumestans | Coumestrol | Clover, alfalfa, spinach |
Phytoestrogens are structurally and/or functionally similar to mammalian estrogens and their active metabolites (Table 1). One major class is the lignans, which are components of plant cell walls and found in many fiber-rich foods such as berries, seeds (particularly flaxseeds), grains, nuts and fruits. Most phytoestrogens, however, are phenolic compounds of which the isoflavones and coumestans are the most widely researched groups. Isoflavones are present in berries, wine, grains and nuts, but are most abundant in soybeans and other legumes 8). The isoflavone content of an array of foods is now published in numerous on-line databases [reviewed in Schwartz et al. 9)] the most accessible of which for consumers is maintained by the USDA (Table 2) United States Department of Agriculture [281].
Table 3. Isoflavone content of a representative sample of food products
| Food product | Genistein (mg/100g) | Daidzein (mg/100g) | Total isoflavones (mg/100 g) |
|---|---|---|---|
| Soy Infant Formula (powder) | 13.5 | 6.32 | 26.3 |
| Edamame (raw green soybeans) | 22.6 | 20.3 | 48.9 |
| Miso | 23.2 | 16.4 | 41.5 |
| Silken tofu | 8.4 | 9.2 | 18.0 |
| Raw tofu, regular | 13 | 9 | 23 |
| Textured soy flour | 89.4 | 67.7 | 172.6 |
| Soy protein isolate | 57 | 31 | 91 |
| Soy-based sliced cheese | 6.5 | 5.1 | 14.5 |
| Soy-based bacon bits | 45.8 | 64.4 | 118.5 |
| Soy-based burgers | 5.0 | 2.4 | 6.4 |
| Red clover | 10 | 11 | 21 |
| Multigrain bread | 0.2 | 0.2 | 0.4 |
| KASHI Go Lean cereal | 7.7 | 8.4 | 17.4 |
| Green tea, Japanese | 0.02 | 0.01 | 0.02 |
| Flaxseeds | 0.04 | 0.02 | 0.07 |
| Raw broccoli | 0.00 | 0.04 | 0.25 |
Table 4. Isoflavones and lignans in various food sources
| Plant species (Common name) | Genistein | Daidzein | Secoisolariciresinol | Metairesinol |
|---|---|---|---|---|
| Soybean | 993-3115 | 413-2205 | < 1-8 | < 1 |
| Kidney bean | < 1-19 | < 1-2 | 2-4 | < 1 |
| American groundnut | 4-30 | < 1 | < 1-2 | < 1 |
| Chicpea | 3-8 | < 1-8 | < 1 | 0 |
| Pea | < 1 | < 1 | < 1 | < 1 |
| Lentil | < 1 | < 1 | < 1 | < 1 |
| Kudzu root | 467 | 7283 | < 1 | < 1 |
| Flaxseed | 0 | 0 | 10-247 | 30 |
| Sunflower seed | < 1 | 6 | 2 | 17 |
| Peanut | 2 | 1 | 8 | < 1 |
| Wheat bran | < 1 | < 1 | 3 | 0 |
| Barley | < 1 | < 1 | 2 | 0 |
| Rye bran | 0 | 4 | 4 | 5 |
| Strawberry | 0 | 0 | 33 | < 1 |
| Cranberry | 0 | 0 | 29 | 0 |
| Bluberry | 0 | 0 | 23 | 0 |
| Rasberry | 0 | 0 | 4 | 0 |
| Red cabbage | < 1 | < 1 | 4 | < 1 |
| Broccoli | < 1 | < 1 | 11 | < 1 |
| Garlic | 0 | 0 | 11 | < 1 |
| Zucchini | 0 | 0 | 23 | < 1 |
| Carrot | 0 | 0 | 10 | < 1 |
| Breetroot | 0 | 0 | 3 | < 1 |
| Black tea | Trace | Trace | 73 | 12 |
| Green tea | Trace | Trace | 75 | 5 |
Types of Food Estrogens
Flavonoids
They are the largest group of plant phenols including more than 4000 different compounds which are the most studied phytochemicals. The basic flavonoid structure allows a multitude of variations in chemical structure, giving rise to flavonols (quercetin, kaempferol, myricetin), flavones (apigenin, luteolin), flavanones (catechin, epicatechin), antocyanidins and isoflavonoids (glycitein, genistein, daidzein) 12). An important effect of flavonoids is the scavenging of oxygen-derived free radicals. The major source of isoflavonoids in the diet is from soy-based foods. The isoflavonoids from legumes, including genistein and daidzein, are the most studied phytoestrogens. They can exist as glycosides or as aglycones, the glucosides being readily hydrolized in the gut as their aglycones. The aglycones are easily transported across intestinal epithelial cells. Genistein has one-third the potency of estradiol when interacts with ERα, and one thousandth of the potency of estradiol when it interacts with ERβ as determined by expression of luciferase reporter gene construct in kidney cells that have been cotransfected with ERα and ERβ 13). Genistein may produce similar effects to estradiol in several different tissues as breast, ovarian, endometria, prostate, vascular , bone tissue and cell lines 14). Furthermore, genistein induce also responses that are not associated with the ER, as the inhibition of tyrosine kinase and DNA topoisomerase 15). Such effect is produced even in the presence of the antiestrogen revealing a non genomic action that could explain a part of the difference between genistein and estradiol.
In vitro experimental systems also showed that flavonoids possess anti-inflammatory, antiallergic, antiviral and anticarcinogenic properties 16) and various of these molecules, notably isoflavonoids, are identified as phytoestrogens being able to bind estrogens receptors, and possess estrogenic or antiestrogenic activities 17).
Lignans
They are constituens of higher plants, such as whole grains, legumes, vegetables and seeds with exceptionally high concentrations of lignans found in flaxseed. Although previously though to be present only in higher plants, mammalian lignans have been detected in the biological fluids of humans and animals. The chemical structure of plant lignans is very different from that of mammalian lignans and most of the changes occur in the colon, liver and small intestine. Enterolactone and enterodiol are metabolites of the plant lignans metairesinol e secoisolariciresinol, respectively 18). A clinical study showed that the excretion of the lignans, enterodiol and enterolactone, was significantly higher during a carotenoid (carrots and spinaches) and cruciferous (broccoli and cauliflowers) vegetable diet, than during a vegetable-free diet 19).
Coumestans
Legumes are the main source of coumestrol, the coumestan showing the highest estrogenic activity, and low level of coumestrol have been found also in brussel sprouts and spinaches, while the highest concentrations are reported in clover and in soybean sprouts.
Stilbenes
Recently, also the stilben resveratrol has been identified as a phytoestrogen. Resveratrol is a natural compound produced by some plants, such as grapevines, in response to injury. Peanuts are rich in resveratrol too. Polygonium cuspidatum roots, which have long been used in traditional oriental medicine, have been identified as the major active source of stilben phytoalexins. Trans resveratrol was firstly detected in grapevines in 1976 by Langcake and Pryce, who found that this compound was synthesized by leaf tissues in response to Botrytis cinerea fungal infection or exposure to ultraviolet light 20).
The biological activity of resveratrol was attested about fifteen years ago by the health benefits obtained by orally administered resveratrol. An experimental study suggested that an average drinker of wine may, in the long term, absorb a quantity of resveratrol sufficient to explain the beneficial effect of red wine on human health 21). Resveratrol possesses anticancer properties, antioxidant activity and some observations have challenged the protective effects of resveratrol against atherosclerosis then preventing cardiovascular diseases. As a phytoestrogen it may favourably influence several physiological processes and given that resveratrol has a different structure, also its mechanism of action might differ somewhat from that of other flavonoids 22).
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