Confused re Soya and Oestrogen positive BC


I read in Prima this week that reaserch in the UA has proven that soya is definitely good for women with oestrogen positive BC.   I’m really confused.  I stopped eating and drinking soya products as advsied by my BC nurse some 6 months ago, but now it soulds like that was the wrong thing to do.  Does anybodyelse have any thoughts on this?

Hi SusieWong,


Diet and foods to include/exclude are one of the most fraught topics and those where the most disinformation gets bandied around the internet.  I have not seen the article, so I can’t comment on it.


I don’t want to teach you to suck eggs, but soy is very high in phyto-oestrogens (plant oestrogens) that can mimic human oestrogen, so will latch onto the  same receptors in cells.  One theory is that phyto-oestrogens are preferentially taken up by cells and are less effective at feeding cancer, ergo soy good.  However, Tamoxifen also works by latching onto these receptors blocking oestrogen from reaching dodgy cells.  If (and some research support this) phyto -oestrogens get there first, they may be preferentially absorbed so reducing the effectiveness of the Tamoxifen, ergo soy bad.


Generally oncologists tells women not to take soy, sage or other phyto-oestrogen rich supplements for hot flushes, and prefer women not to increase the level of soy in their diet.  I made a choice, having read the research at the time (two years ago) to exclude soy from my diet, as I need the Tamoxifen to do its utmost for me.


You will probably not get a definitive answer to your question, it is something only you can decide, but why not show the article to your oncologist or GP and see what they think.  Remember they will have access to UK research which may be more robust or relevant than something quoted in a magazine.



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Like Revcat, I’m on tamoxifen and exclude soy, but I have been taking sage supplements to help with hot flushes.  Going to seek further advice from onc now… 

thanks Sarah

Hi again Susiewong,

Can you say which issue of Prima this was in?  I just went and bought one in a local shop (September 2013) and could not find the articles (or anything like them) but would be interested to read them, even if I would then be off to find scientific papers to support/refute them!  I would always as a minium look at CRUK, BCC and MacMillan and am the annoying type who also looks at oncology journals!!


As far as caffiene goes the only thing I’ve been told is that it can be a trigger for hot flushes.  Like a lot of things there are balances to be struck - caffiene may be beneficial in some ways but will be detrimental on others.  The best advice is to have a varied, balanced diet with a ‘bit of what you fancy’ and to check with your GP or oncologist before taking any supplements or starting new diets.


Hope that helps a little bit.

I eat soy and am not worried about it.

This subject does my head in to be honest. I have researched this to death and cannot find an answer. I have been drinking soya milk for years but read that other day that it was a little dodgy as it has natural oestrogen, so I have stopped now. But then about 5 mins ago read it was good to drink. No one seems to know for sure which  is rather worrying. I was diagnosed with DCIS 2 weeks ago and really would like to know if I have made this worse, if it was my faulty so to speak. I don’t want it coming into the other breast due to soya milk, or not drinking soya milk. Sorry I haven’t helped much.

Phyto-oestrogens are not the same thing as female oestrogens. Soy foods do not contain oestrogen.  There isn’t any hard evidence one way or the other re. soy and promotion of BC. 


I bought the October edition of Prima and have now read the articles, which to be honest seem to me to be full of sweeping generalisations - useful for the general public but  not so useful for the 1 in 8 who happen to have bc in my opinion  (I went down their checklist: exercise - tick, coffee - tick, five a day - tick, slim(ish) - tick, no alcohol- tick… still got breast cancer - tick… )


I then tried to track down the original research to support the claim about soya without success - it should be findable in some learned journal and/or on the AICR website and it appears not to be, at least as yet.


I did find some other research papers which seem to suggest that these results won’t ‘end years of uncertainty’ in the sweepingly generalised way the article suggests.  Presumably they were studying women with ER+ cancer  but it is not evident whether these were women taking Tamoxifen etc or what their menopausal status was etc. etc.  What little research I found seemed to focus on women who were less than two years post diagnosis which, albeit often seen as the highest risk period for recurrence, is not the whole picture by any means.


It was careful study of research papers on tamoxifen and soy interactions that informed my decision to actively exclude it from my diet; this article does not convince me otherwise.


Sorry, this reply doesn’t help anyone make sense of the confusion - I think that if you want more advice you should speak to your oncologist

I’ve not read the Prima article, but a few months ago I read an article on the American Cancer Society website  (dated just over a year ago): 


The Cancer Society article  concludes:   “Even though animal studies have shown mixed effects on breast cancer with soy supplements, studies in humans have not shown harm from eating soy foods. Moderate consumption of soy foods appears safe for both breast cancer survivors and the general population, and may even lower breast cancer risk. Avoid soy supplements until more research is done. So, enjoy your occasional tofu stir-fry or tofu burger - they are unlikely to increase your risk of breast cancer and, on balance, are some of the healthier foods you can eat!”


The author is the strategic director of nutritional epidemiology for the Amercan Cancer Society, so  would expect anything he/she writes on this topic to be more reliable than the Prima article (presumably written by a journalist?) Journalists are not experts and even when they are writing for newspapers or well-known magazines, they sometimes don’t do their homework as well as you might expect (although I can’t make a judgement on the Prima article, not having read it).