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What is the Relationship Between Soy and Breast Cancer?

Erin J. Hill
Erin J. Hill

The exact relationship between soy and breast cancer is unclear. Studies have shown that women who begin consuming soy-based foods early in life have lowered breast cancer rates than those who do not consume soy. Additional studies have shown that women who consume soy after menopause may have an increased risk of developing breast cancer. This is also true for women who have had the disease previously.

Soy and soy-based products come from soy beans and they are used in a wide array of vegetarian dishes. They have been used in Asian cuisine for thousand of years, and they are often used to replace meat and dairy products for those who can’t or don’t eat them. Soy contains isoflavones, or phytoestrogens, which react and affect the body much in the same way that natural estrogen does. These phytoestrogens are much weaker than natural estrogen, however, when consumed in food sources.


Isoflavones are high in antioxidants, which are cancer preventers. The link between soy and breast cancer seems to indicate that women who consume soy based foods starting before puberty have the lowest breast cancer rates. This was concluded when a large study of Asian women, who eat soy starting in childhood, were tested for phytoestrogen levels in the bloodstream. Those who had the highest numbers also had the lowest breast cancer rates.

Links between soy and breast cancer have not been definitively proven.
Links between soy and breast cancer have not been definitively proven.

These protective effects seem to be reversed for those who begin consuming soy in their later years. In postmenopausal women, soy and breast cancer development may be linked. Since the isoflavones in soy mimic real estrogen, they can fuel growth of estrogen dependent tumors. This is especially true for women who have a strong family history of breast cancer, who are also taking estrogen supplements, or who have suffered from cancer in the past.

Food sources of soy have much fewer estrogenic effects than soy-derived supplements. For this reason, young women who have no history of breast cancer can generally consume soy safely. They may even get added protection against cancer. Women who are postmenopausal or who have had breast cancer previously should not consume soy, especially supplements unless directed by a doctor.

These links between soy and breast cancer have not been definitively proven. There is still much debate on whether soy prevents or causes cancer, although the link between cancer development and age is well established. Women should do independent research on this topic and discuss it with their doctors to determine the benefits or risks of eating soy.

Discussion Comments


@literally45-- You should speak to your doctor about it.

Some doctors allow their patients to use plants with estrogen to relieve some of the symptoms of menopause. But if the patient has a risk of breast cancer or has a breast growth, then estrogen is not allowed in any form. It's best to find out by asking your doctor.

My mother is in menopause and she cannot take anything with estrogen or phytoestrogen. She has a benign growth in her breast and her doctor is afraid that the growth may grow further or turn malignant if she receives any estrogen.

Plus, menopause, as difficult as it may be, is a natural process. Estrogen reasons fall for a reason. We should not try to increase it.


I recently entered menopause. My doctor has not said anything about soy to me, or other foods and herbs containing phytoestrogen. I do consume soy milk and tofu regularly. Should I be worried?


I think the fact that women who eat soy since puberty have less breast cancer is a coincidence. The study was done on Asian women and we all know that breast cancer is a hereditary illness. So it may just be that Asian women are less likely to get breast cancer. I don't find that study conclusive at all on the matter.

If soy ever had a preventative effect on breast cancer, it probably doesn't anymore. I can't say anything about soy that was produced hundreds of years ago. But I have read that as of 2010, all soybeans in the world are genetically modified foods. For that reason alone, I don't believe that the soy we eat today can prevent cancer.

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    • Soybeans.
      By: terumin
    • Links between soy and breast cancer have not been definitively proven.
      By: rob3000
      Links between soy and breast cancer have not been definitively proven.