Genistein / Soy

Also known by these names

Soy foods may have several other labels:

  • Bean curd
  • Edamame
  • Kinnoko flour
  • Kyodofu
  • Miso
  • Natto
  • Okara
  • Shoyu sauce
  • Soy milk
  • Soya
  • Supro
  • Tamari
  • Tempeh
  • Textured vegetable protein
  • Tofu
  • Yakidofu
  • Yuba

Key Points

  • Soy contains large amounts of isoflavones, including genistein.
  • In laboratory studies, isoflavones have slowed the growth of several types of cancer.
  • BCCT is interested in soy because it may reduce risk of breast, prostate and lung cancers, plus colorectal cancer in women. It may also prolong survival and reduce recurrence in some cancer patients.
  • Soy can increase risk of bladder cancer and endometrial hyperplasia, although some evidence also shows that soy can reduce the risk of endometrial cancer.
  • Cell and animal studies have shown that adding soy food nutrients to tamoxifen inhibits the growth of estrogen receptor positive (ER+) breast cancer cells.
  • Not enough information about soy supplements, such as concentrated isoflavones, has been assessed to determine if they are safe.
  • Soy or genistein can interfere or interact with a few other prescription medications.

The beans of the soy plant contain isoflavones, a type of phytoestrogens which are chemical structures similar to the estrogen made in our bodies. However, phytoestrogens are not the same as female estrogens. Soy foods do not contain estrogen.1

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Treating the Cancer

Working against cancer growth or spread, improving survival, or working with other treatments or therapies to improve their anticancer action

Clinical Evidence

Evidence is generally favorable but sometimes inconclusive.

Breast Cancer

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Lung Cancer

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Ovarian Cancer

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Prostate Cancer

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Lab and Animal Studies

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Managing Side Effects and Promoting Wellness

Managing or relieving side effects or symptoms, reducing treatment toxicity, supporting quality of life or promoting general well-being

Soy isoflavones show slight and slow effects in attenuating menopausal hot flashes compared with estradiol20 but greater effects than placebo.21

Reducing Risk

Reducing the risk of developing cancer or the risk of recurrence

Clinical Evidence

Soy consumption is associated with reduced risk of some cancers but increased risk of others.

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Lab and Animal Evidence

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Soybeans and foods derived from soybeans are widely available. Extracts are sold as dietary supplements.


While in the past patients on tamoxifen were advised to avoid soy and genistein, more recent data suggest that soy does not reduce effects of tamoxifen and may even protect against estrogen-related endometrial cancers.

Soy foods are generally well tolerated by patient. Interactions with a few prescription medications are noted.31

“Regular ingestion of moderate amounts of soy daily seems to be safe—especially with the traditional fermented soy foods such as miso, tempeh, and natto when made from organic non-GMO soybeans."32

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BCCT does not recommend therapies or doses, but provides information for patients and providers to consider as part of a complete treatment plan. Patients should discuss therapies with their physicians, as contraindications, interactions and side effects must be evaluated. Levels of active ingredients of natural products can vary widely between and even within products. See Quality and Sources of Herbs, Supplements and Other Natural Products.

Dosage recommendations are available from these sources:

Integrative Programs, Protocols and Medical Systems

For more information about programs and protocols, see our Integrative Programs and Protocols page.
  • Programs and protocols
    • Ovarian cancer
    • Prostate cancer
    • Primary bone cancer (such as osteosarcoma)
    • Uterine cancer
    • Alschuler & Gazella complementary approaches36
    • Block program, , with reference to prostate cancer37
    • Chang strategies, , with reference to prostate cancer38
    • McKinney protocols39
      • General cancer
      • Breast cancer
      • Ovarian cancer
      • Prostate cancer
  • Traditional systems

Non-cancer Uses of Soy/Genistein

BCCT has not reviewed the effectiveness of this therapy for non-cancer uses.

  • Prevent heart disease
  • Reduce high cholesterol
  • Treat menopause symptoms
  • Prevent bone loss

Written by Laura Pole, RN, MSN, OCNS, and Nancy Hepp, MS; most recent update April 6, 2019. This summary draws from the Memorial Sloan Kettering Cancer Center’s About Herbs and National Cancer Institute’s PDQ® websites, the American Institute for Cancer Research website, and other sources as noted.

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