Phytoestrogens

Phytoestrogens are plant compounds with structures similar to estrogen, which give them the ability to cause estrogen-like effects on the body.  Examples include:

  • Isoflavones from soy, lentils, and legumes
  • Lignans from flaxseed, cereal grain, and vegetables
  • Coumestans from red clover, sunflower seeds, and bean sprouts

Research on phytoestrogens has been promising yet inconsistent in showing improvements in menopausal symptoms.  The variation in therapeutic effects of phytoestrogens in the treatment of menopause may be influenced by a woman’s intestinal bacteria and its ability to metabolize phytoestrogens into therapeutic substances in the body (i.e. converting daldzein into equol).[1]

Hot flashes.  The North American Menopause Society’s isoflavones report from 2011 concluded, “there are mixed results of the effects on midlife women.  Soy-based isoflavones are modestly effective in relieving menopausal symptoms.”[2]  Multiple meta-analyses have documented improved frequency of hot flashes with use of isoflavones in doses ranging from 50-100 mg daily.[1][3][4][5][6]

Vaginal dryness.  Soy isoflavones showed improvement in vaginal symptoms (dryness, irritation, painful intercourse) when compared to control in a systematic review of 17 trials.[7]

Overall health.  A systematic review of 23 randomized controlled trials concluded that phytoestrogens likely have beneficial effects on bone health in menopausal women.[8]  A meta-analysis showed that soy isoflavone supplementation (60-120 mg/day) has a positive effect on cognitive function and visual memory in postmenopausal women.[9]

Some women may find that eating a diet high in phytoestrogens helps their menopausal symptoms, in addition to providing other health benefits.  In some Asian cultures, where women consume 50-200 mg of isoflavones daily, hot flashes are rare as compared to Americans, whose typical diets contain only 3-5 mg daily.  Soy, in particular, improves cholesterol levels and is a great plant source of protein.  The highest quantities of isoflavones are found in less-processed foods and fermented soy products.  The best food sources include soybeans or edamame, soy nuts, tofu, tempeh, and miso (refer to Table 1).

Table 1. Amount of Isoflavones per Serving of Soy

wdt_ID Soy product Approx. amount of isoflavones (milligrams)
1 Tofu, 3 ounces 20
2 Soy beans, ½ cup 47
3 Soy milk, 8 ounces 30
4 Miso, ½ cup 59
5 Tempeh, 3 ounces 37

Flaxseed is another great source of phytoestrogens, fiber, and alpha-linolenic acid (a source of omega-3 fatty acids).  As opposed to flaxseed oil, the seeds must be ground in order for them to be adequately digested.  They can be sprinkled on salads, yogurt, smoothies, or cereal.  A small study of 30 women showed that eating 2 tablespoons of flaxseed twice daily decreased their total number of hot flashes by half after six weeks.  Hot flash intensity also decreased.[10]

Women may consider maximizing these healthy foods in their diets, with a goal of 50-100 mg of isoflavones daily.  These foods may cause some bloating and increased gas, so intake should be increased gradually.  Refer to the section below for a list of foods high in phytoestrogens.

Historically, women with estrogen-sensitive conditions were counseled against high isoflavone intake due to the concern of stimulating cancer growth.  Population studies suggest that dietary soy is protective against breast and uterine cancers.[11]  Women with a history of breast, ovarian, or uterine cancer should discuss with their oncologist before using isoflavone supplements.  For more information on the use of soy, a particular type of phytoestrogen and its use in breast cancer, refer to the Whole Health “Cancer Care” overview.

Table 2. Foods High in Phytoestrogens

Vegetables

  • winter squash
  • green beans
  • collard greens
  • broccoli
  • cabbage
  • alfalfa sprouts

Fruits

  • dried prunes
  • peaches
  • raspberries
  • strawberries

Grains

  • wheat
  • rye
  • oats
  • barley

Beans

  • soybeans
  • lentils
  • navy, kidney, pinto beans

Seeds and Nuts

  • flaxseed
  • sesame seeds
  • pistachios
  • sunflower seeds
  • almonds

Author

“Phytoestrogens” was written by Anne Kolan, MD (2014, updated 2020).

This Whole Health tool was made possible through a collaborative effort between the University of Wisconsin Integrative Health Program, VA Office of Patient Centered Care and Cultural Transformation, and Pacific Institute for Research and Evaluation.

References

  1. Daily JW, Ko BS, Ryuk J, Liu M, Zhang W, Park S. Equol decreases hot flashes in postmenopausal women: a systematic review and meta-analysis of randomized clinical trials. J Med Food. 2019;22(2):127-139.
  2. The North American Menopause Society. The role of soy isoflavones in menopausal health: report of The North American Menopause Society. Menopause. 2011;18(11):732-753.
  3. Chen MN, Lin CC, Liu CF. Efficacy of phytoestrogens for menopausal symptoms: a meta-analysis and systematic review. Climacteric. 2015;18(2):260-269.
  4. Franco OH, Chowdhury R, Troup J, et al. Use of plant-based therapies and menopausal symptoms: a systematic review and meta-analysis. JAMA. 2016;315(23):2554-2563.
  5. Perna S, Peroni G, Miccono A, et al. Multidimensional effects of soy isoflavone by food or supplements in menopause women: a systematic review and bibliometric analysis. Nat Prod Commun. 2016;11(11):1733-1740.
  6. Myers SP, Vigar V. Effects of a standardised extract of Trifolium pratense (Promensil) at a dosage of 80mg in the treatment of menopausal hot flushes: A systematic review and meta-analysis. Phytomedicine. 2017;24:141-147.
  7. Ghazanfarpour M, Sadeghi R, Roudsari RL. The application of soy isoflavones for subjective symptoms and objective signs of vaginal atrophy in menopause: a systematic review of randomised controlled trials. J Obstet Gynaecol. 2016;36(2):160-171.
  8. Abdi F, Alimoradi Z, Haqi P, Mahdizad F. Effects of phytoestrogens on bone mineral density during the menopause transition: a systematic review of randomized, controlled trials. Climacteric. 2016;19(6):535-545.
  9. Cheng PF, Chen JJ, Zhou XY, et al. Do soy isoflavones improve cognitive function in postmenopausal women? A meta-analysis. Menopause. 2015;22(2):198-206
  10. Pruthi S, Thompson SL, Novotny PJ, et al. Pilot evaluation of flaxseed for the management of hot flashes. J Soc Integr Oncol. 2007;5(3):106-112.
  11. Natural Medicines Comprehensive Database. Soy. 2020; Natural Medicines Comprehensive Database website. https://naturalmedicines.therapeuticresearch.com/databases/food,-herbs-supplements/professional.aspx?productid=975#adverseEvents. Updated March 5, 2020. Accessed March 22, 2020.

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