Oh wow, thank you so much for all this info! That has really helped reassure & clarify things. Thank you for all the links too; I really appreciate your detailed response 🙏 best wishes, AnnieV x
Thanks for your post.
Information about naturally occurring phytoestrogens, such as soy and it’s effect on breast cancer can be confusing and conflicting.
Soy contains isoflavones and lignans, which are weak phytoestrogens.
Phytoestrogens are naturally occurring plant substances that have a chemical structure similar to the female hormone oestrogen which is why there has been concern about its safety. But phytoestrogens are not the same thing as female hormones and don’t affect the body in the same way.
Soy food includes tofu, soybeans (edamame) and soy milk. There isn’t any evidence to suggest a moderate amount of soy in a person’s diet is harmful.
Isoflavones are also found in other beans, nuts, peas and lentils and lignans are found in a variety of fruits, vegetables and cereal products.
In fact, there is emerging research that suggests it may be beneficial in reducing the risk of the cancer coming back.
The safety of supplements containing soy is yet to be established so they are generally not recommended. You may be interested in the information we produce about a healthy well balanced diet.
You can search this American website here for information about individual herbs and vitamins. Each has sections on existing evidence and what known interaction there is with other medications.
If you take prescribed or over the counter medicine, do check again with your treatment team, your GP, or a pharmacist before taking any supplements.
You can also view our video on dietary tips after a breast cancer diagnosis.
The 2018 World Cancer Research Fund (WCRF) report, page 39.
UpToDate ( Accessed Aug 2020) Soy/phytoestrogens
NICE Do not offer soy (isoflavone), red clover, black cohosh, vitamin E or magnetic devices to treat menopausal symptoms in women with breast cancer. 
CRUK (Last updated June 2019) Herbal medicine
CRUK (Last updated Jan 2019) Vitamins and diet supplements
NHS (Last updated Dec 2018) Complementary and alternative medicine
GOV. UK (Last updated Jan 2021) Traditional herbal registration (THR)
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@AnnieV - great question, the research is so confusing and conflicting isn’t it. I too would be interested to read the answer. My consultant is very much of the view of everything in moderation. Thanks for sending this question. Evie xx
I would also welcome an answer to the questions you have posed. I was taking “Menopace” multi-vitamins (contain isoflavones) for years and asked my BCN (after diagnosis but before my results were known) about continuing with them. I was told to stop the vitamins. I’m ER8/PR8 and now on hormone therapy (letrozole). I’m confused on whether to avoid natural soy products as I regularly use chick peas in soups and meals.
Best wishes x
Since being diagnosed with ER+ PR+ Her 2- breast cancer I have read a lot of conflicting information about naturally occurring phytoestrogens (such as in soya, chickpeas and linseed oil) and whether they are beneficial, indifferent or harmful for those with breast cancer. The breastcancercare booklet I read yesterday about menopausal symptoms says that naturally occurring phytoestrogens are safe for breast cancer patients but supplements are not recommended. This fits with what the oncology dietitian told me at my hospital.
However, I asked the same question to my BCN and in her reply she attached some literature from Women's Health Concern (part of the British Menopause Society) and in this it said that foods with naturally occurring phytoestrogens are not recommended for patients with breast cancer. Although it did not say why; as in whether there is no evidence that they offer a benefit or whether they are actually harmful.
I don't know now whether to avoid foods with naturally occurring phytoestrogens or whether to increase them in my diet! Before my diagnosis I routinely ate houmous (chickpeas) and sometimes soy source, so it is not as if I have never had them.
Are you able to clarify things please? I realise how out-of-date research can go and I don't know what the latest evidence is.