What are Phytoestrogens?

Phytoestrogens are estrogen hormone-like chemicals found in plants. Examples of phytoestrogens are isoflavones (genistein, daidzein), flavones, coumestans and lignans. What makes this group of estrogen-like chemicals of medical and nutritional interest is that their chemical structure is similar to estrogen. And when consumed, depending on their concentration in the diet and concentration of sex hormones in the body, life stage and gender, they can have estrogenic effects (have the same effects as estrogen) or anti-estrogenic effects (inhibit or suppress the effects of estrogen).

What Are the Benefits of Phytoestrogens?

Several studies associate phytoestrogens with reduced risks of breast cancer, prostate cancer, and cardiovascular diseases. Other phytoestrogen health benefits are reduced osteoporosis (bone loss) and menopausal symptoms. Both flavonoid and lignan phytoestrogens also have antioxidant activity.

The low incidence of the above mentioned diseases in Asian populations is partly believed to be associated with their traditionally soy based diet, which is high in phytoestrogens. On average, Asians consume 50mg of isoflavones per kg body weight per day, while Americans on Western-diet consume 1 - 3 mg of isoflavones per kg body weight per day. Isoflavones are one of the phytoestrogens.

Medical phytoestrogen formulations are used by women in menopause as alternatives or complementary options to hormonal replacement therapy (HRT) because of concerns of side-effects or other considerations. Some studies also report potential benefits of phytoestrogens in lowering serum cholesterol levels.

What Are the Side Effects of Phytoestrogens?

Phytoestrogens act like estrogens in the body. This mimicry depending on the dosage of the phytoestrogens and life stage of the person may potentially have side effects. For example, a review of multiple studies reported an association between increased intake of isoflavones and menustrual cycle length and decreased LH and FSH levels, in pre-menopausal women. Animal studies also suggest that phytoestrogens consumed during gestation and early infancy influence brain and reproductive systems development.

What Foods are High in Phytoestrogens?

Estrogen is available in medically formulated pills. However, dietary estrogen (phytoestrogen) can also be found naturally in wide variety of plant-based foods, with the amount varying depending on the plant type. The main food sources of phytoestrogen are soybean and flaxseed, and their derivatives. Other food types such as nuts, oil seeds and herbs are also good sources phytoestrogens, eventhough in relatively low concentrations.

The type of phytoestrogens and their relative concentration varies from plant to plant. For example, isoflavone phytoestrogens are found in high concentration in soybean and soybean food products (eg. tofu) whereas lignan phytoetrogens are found mainly in flax seed.

Canadian researchers analyzed 121 food types including fruits, vegetables, herbs, grains, nuts and oils for their phytoestrogen content. The food types, as reported in the study, with the highest total phytoestrogen content are listed in the two tables below.

The phytoestrogen contents are averages based on analyses of multiple samples.

Table 1. Foods high in phytoestrogens content. The total phytoestrogens content is the sum of isoflavones (genistein, daidzein, glycitein, formononetin), lignans (secoisolariciresinol, matairesinol, pinoresinol, lariciresinol), and coumestan (coumestrol). (1 µg = 0.000001 g)

Phytoestrogens food sources Phytoestrogens content (µg/100g) Flax seed 379,380 Soy beans 103,920 Soy nuts 68,730.8 Tofu 27,150.1 Tempeh 18,307.9 Miso paste 11,197.3 Soy yogurt 10,275 Soy protein powder 8,840.7 Sesame seed 8,008.1 Flax bread 7,540 Multigrain bread 4,798.7 Soy milk 2,957.2 Hummus 993 Garlic 603.6 Mung bean sprouts 495.1 Dried apricots 444.5 Alfalfa sprouts 441.4 Pistachios 382.5 Dried dates 329.5 Sunflower seed 216 Chestnuts 210.2 Olive oil 180.7 Almonds 131.1 Cashews 121.9 Green bean 105.8 Peanuts 34.5 Onion 32 Blueberry 17.5 Corn 9 Coffee, regular 6.3 Watermelon 2.9 Milk, cow 1.2

Lignans are one of the phytoestrogens. In table 2 are foods measured for their total phytoestrogen content and the lignan fraction.

Table 2. Total phytoestrogens and lignan content in vegetables, fruits, nuts and drinks.

Food items Lignan content (µg/100g) Total phytoestrogens (µg/100g) Vegetables Soy bean sprouts 2.2 789.6 Garlic 583.2 603.6 Winter squash 113.3 113.7 Green beans 66.8 105.8 Collards 97.8 101.3 Broccoli 93.9 94.1 Cabbage 79.1 80 Fruits Dried prunes 177.5 183.5 Peaches 61.8 64.5 Strawberry 48.9 51.6 Raspberry 37.7 47.6 Watermelon 2.9 2.9 Nuts and other legume seeds Pistachios 198.9 382.5 Chestnuts 186.6 210.2 Walnuts 85.7 139.5 Cashews 99.4 121.9 Hazel nuts 77.1 107.5 Lentils 26.6 36.5 Beverages Wine, red 37.3 53.9 Tea, green 12 13 Wine, white 8 12.7 Tea, black 8.1 8.9 Coffee, decaf 4.8 5.5 Beer 1.1 2.7 Other Black bean souce 10.5 5330.3 Black licorice 415.1 862.7 Bread, rye 142.9 146.3

Isoflavones are one of phytoestrogens. Here is a list of foods measured for isoflavones only.

Table 3. Isoflavones content in select foods.

Food list Total isoflavones content

(mg/100 g) Textured soy flour 172.6 Soy-based bacon bits 118.5 KASHI Go Lean cereal 17.4 Soy protein isolate 91 Edamame (raw green

soybeans) 48.9 Miso 41.5 Soy Infant Formula (powder) 26.3 Raw tofu, regular 23 Red clover 21 Silken tofu 18.0 Soy-based sliced cheese 14.5 Soy-based burgers 6.4 Multigrain bread 0.4 Raw broccoli 0.25 Flaxseeds 0.07 Green tea, Japanese 0.02



Phytoestrogen related articles:

Food sources of lignan phytoestrogens

Dietary Intake of Phytoestrogens Cuts the Risk of Colorectal Cancer

Description and the effect of phytoestrogens in the body?

Estrogens: What they are, functions, and synthesis

Phytoestrogens, osteoporosis and menopausal women

Tofu: phytoestrogen and health benefits

Phytoestrogen data source:

Thompson, L. U., Boucher, B. A., Lui, Z., Cotterchio, M., and Kreiger, N. 2006. Phytoestrogen content of foods consumed in Canada, including isoflavones, lignans and coumestan. Nutrition and Cancer, 54(2), 184-201.



Additional references:

Cassidy A. Potential risks and benefits of phytoestrogen-rich diets. Int J Vitam Nutr Res. 2003 Mar;73(2):120-6.



Ganry O. Phytoestrogens and prostate cancer risk. Prev Med. 2005 Jul;41(1):1-6.

Heather B. Patisaul and Wendy Jefferson. The pros and cons of phytoestrogens. Front Neuroendocrinol. 2010 Oct; 31(4): 400–419.

Tham DT, Gardner CD, Haskell WL. Potential health benefits of dietary phytoestrogens: a review of the clinical, epidemiological, and mechanistic evidence. J Clin Endocrinol Metab. 1998; 83(7):2223-2235.