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Soy Proven To Be Good For Breast Cancer Survivors
Just in case we had any lingering questions in our minds as to whether it is safe to eat soy after breast cancer, a brand new study confirms that it is not only safe but protective. We have a BUNCH of these studies now, yet this is one of the things I am asked with great frequency. I have written several articles about it for my website (links below) but there still seems to be so much misinformation given to women with breast cancer about soy.
If you don’t want to read this entire article, here’s the bottom line – minimally processed organic soy foods are considered safe and healthy to eat. The important takeaway – if you are going to eat soy for preventive purposes, it needs to be the type of soy that is not highly processed – whole soy such as tempeh, miso, edamame, tofu, soy milk, soy sauce. And always choose organic, non-GMO soy.
Do I eat soy? Yes! I do choose frequently to eat and enjoy whole organic soy foods. Things like miso, tofu and edamame are things I include in my diet fairly often. There are so many great recipes and dishes that include these healthy soy options. And yes, soy does need to be organic because so much of it is now genetically modified and that has not been proven to be safe for us.
Now for the rest of you that want all the nitty gritty research…
I love reading new research, especially when it helps us understand new things that relate to breast cancer. I love it when new research debunks old ways of thinking because it helps you to decide for yourself whether or not to give something a try. PLEASE don’t base your decision to not have soy products on something your doctor told you – mainly because many doctors are not up to speed on the latest nutrition research. I believe it’s up to us to teach them!
What’s The Perceived Problem with Soy and Breast Cancer?
The main reason we have, in the past, been warned off having soy products after breast cancer is because soybeans contain compounds known as isoflavones. Isoflavones act like weak estrogens, also termed phytoestrogens. The estrogen-like properties of soy have raised concerns in the past for women with estrogen-receptor-positive breast cancer, which is the main type of breast cancer. The worry is that the phytoestrogens might potentially influence cancer to grow. But that theory has not been proven, quite the contrary. What we are finding is that phytoestrogens occupy estrogen receptor sites on cells, preventing stronger estrogen from the body (and also environmental estrogens known as xenoestrogens) from exerting their more powerful influence. So phytoestrogens appear to have a protective and balancing effect on hormones.
The New Research
The latest study, appearing in the journal Cancer in June 2017 1 investigated the effects of soy isoflavones on breast cancer survivors. The National Cancer Institute-funded study collected data from the Breast Cancer Family Registry for 6,235 breast cancer patients over a period of 113 months (9.4 years). The program collected clinical and dietary data on participants and researchers specifically analyzed the soy intake of these women. They found that:
1. Eating foods rich in soy isoflavones was associated with reduced all-cause mortality;
2. A 21 percent decreased risk of death was enjoyed among women eating the highest amount of soy foods. This was also true for women with hormone-receptor-negative breast cancer AND women who did not have hormone therapy.
This is really interesting! The study tells us that soy isoflavones have a beneficial impact on women with breast cancer, regardless of whether their tumor was hormone-receptor positive or negative, also regardless of whether or not the women received hormone therapy such as Tamoxifen.
But Wait… There’s More!
This is not the only study on soy and breast cancer. I have four other, older, studies to share with you. In May 2012 a joint study 2 between Chinese and American researchers, published in the American Journal of Clinical Nutrition followed 9,514 breast cancer survivors in America and China between 1991-2006. Those who consumed soy and its isoflavones had significantly reduced mortality from breast cancer and a “statistically significant reduced risk of recurrence.”
Canadian researchers investigated the same thing in 2013. The title of the study was Soy, Red Clover, and Isoflavones and Breast Cancer: A Systematic Review 3. Basically, they investigated various medical databases looking for human interventional or observational data relating to the safety and efficacy of soy and red clover isoflavones for patients with breast cancer, or at high risk. They concluded: “Soy consumption may be associated with reduced risk of breast cancer incidence, recurrence, and mortality. Soy does not have estrogenic effects in humans. Soy intake consistent with a traditional Japanese diet appears safe for breast cancer survivors. While there is no clear evidence of harm, better evidence confirming safety is required before use of high dose (=100mg) isoflavones can be recommended for breast cancer patients.”
In addition to that, an American study published in Anti-Cancer Agents in Medicinal Chemistry in 2013 4 also reviewed past studies and compared the available literature, looking at the anti-cancer vs cancer-promoting effects of soy isoflavones in humans and animals. Researchers concluded “it appears that soy isoflavones do not function as an estrogen, but rather exhibit anti-estrogenic properties. However, their metabolism differs between humans and animals and therefore the outcomes of animal studies may not be applicable to humans. The majority of breast cancer cases are hormone-receptor-positive; therefore, soy isoflavones should be considered a potential anti-cancer therapeutic agent and warrant further investigation.”
In a 2014 meta-analysis, which is a study that analyzes all of the research on a particular topic, published in the journal PLOS-One by Chinese researchers 5, it was found that eating soy helped to prevent breast cancer in women of all ages. Researchers found that eating soy cut the risk of breast cancer by a whopping 41 percent!
Important precautions: Supplements and protein powders containing soy protein isolate and concentrated sources of isoflavones DO appear to stimulate the growth of estrogen-dependent tumors and should be avoided. Also avoid highly processed soy products such as soy flour, soy oil, silken tofu, TVP (texturized vegetable protein) and soy isoflavone supplements. These are not proven to be good for our health. Lastly, always choose organically grown soy because so much of our soy is now genetically modified and this has not been proven to be safe for human consumption.
In the end, you must do whatever feels right for you. If it’s not a good fit for you, for instance if you hate the taste or texture of tofu, no problem! Move on to something else. There are plenty of anti-cancer foods – see my page Diet and Cancer for more ideas. If you have soy allergies, obviously eating soy is not going to help you. But eating a mainly plant-based diet is hugely beneficial and helps to cut the risk of breast cancer by a huge degree (especially when combined with exercise).
Other articles that may be of interest: Phytoestrogens – Harmful Or Beneficial For Hormone Driven Breast Cancer?
Is Soy Bad For Women with Breast Cancer? A Definitive Answer
 Dietary isoflavone intake and all-cause mortality in breast cancer survivors: The Breast Cancer Family Registry – https://www.ncbi.nlm.nih.gov/pubmed/28263368
 Soy Food Intake after Diagnosis of Breast Cancer and Survival: an In-depth Analysis of Combined Evidence from Cohort Studies of Us and Chinese Women – https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3374736/
 Soy, Red Clover, and Isoflavones and Breast Cancer: A Systematic Review – https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3842968/
 Soy and its Isoflavones: the Truth Behind the Science in Breast Cancer – https://www.ncbi.nlm.nih.gov/pubmed/23919747
 Soy food intake after diagnosis of breast cancer and survival: an in-depth analysis of combined evidence from cohort studies of US and Chinese women – https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3374736/
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Thanks for all info , took soy supplements but heard the risk so stopped them . Then heard soy diet was good so continued on soy ,I’m vegan so everything I read here tells me I’m doing the right thing . Tried to discuss this with my GP but was dismissed with ‘ I don’t know anything about it ” have to say I’ve recieved little or no help from GP or any aftercare . Quite disgusted with it to be honest.
But I’ll continue with alternative remedies as I’m A Reiki Master ( non practising now ) but use my knowledge on myself and others if asked . So all in al GPs nil alternative 100%
Very pleased I’ve found a very helpful site , thanks very much
Now to make sure I’ve signed up properly , still suffering fro Tamoxifen brain but beginning to improve since starting co enzyme Q 10. X
While it’s true that soy is protective, it’s WHOLE SOY products and fermented soy products that are proving to be protective against breast cancer. Just make sure to stay away from anything that has “soy protein isolate” in it, because this has been associated with increased risk of breast cancer. I’m glad you are enjoying my website, and thanks for commenting. (Oh and kudos for finding something to help your “Tamoxifen brain”. Try essential oils of frankincense, lavender, cedarwood, elemi and sandalwood as well!)
Dear Marnie, great information on soy and probiotics . I have been afraid to eat soy because of my hypothyroidism. I am on Aromasin and it’s been 2 years since diagnosis of estrogen and progesterine positive breast cancer. Do you have any information on if it’s okay to consume when a person has more than one issue going on. Thanks, Simone
I’ve just sent you links to two studies indicating that eating whole soy foods was protective for breast health and did not appear to pose a risk for hypothyroid individuals. Just make sure to avoid soy protein isolate, eat whole soy foods and fermented soy and you should be fine. Hope that helps!
All the best
Hi Marnie, I want to make sure I am understanding you and all this information regarding soy in my diet. I am triple positive and thought I had read for Her2 + BC NOT to eat soy. Please help me to understand and do what’s best for my health and my future.
Thank you for all your wonderful helpful information.
Soy is actually okay for HER2 positive people and it’s extremely protective for those with ER+, which you also are. You just want to avoid “soy protein isolate” which can be found in soy supplements and some protein powders. That particular soy isolate does appear to cause troubles and promotes proliferation (rapid growth) of breast cancer cells. Whole soy products are really good for you though. Now, as to diet for you, some good recommendations appear on this page: https://marnieclark.com/the-best-diet-for-her2-positive-breast-cancer/ If you’d like some help with putting together a holistic healing plan, I’ve emailed you my coaching info.