The-latest-on-soy-and-breast-cancer

Soy rivals coconut oil as the most confusing and contentious food item amongst people I meet with. For prevention and recovery, naturopaths and doctors alike have conflicting views and often express them with some passion.

Previous blogs (see references below) have catalogued the science and shared the clinical experiences that inform my own opinions, yet still the questions seem to linger. New research has emerged to throw fresh light on what has been a long and often emotional debate, so this week, some more clarity, but first




               Thought for the day

     When one door closes another door opens; 
     But we so often look so long 
     And so regretfully upon the closed door, 
     That we do not see the ones which open for us. 

                              Alexander Graham Bell




Soy and breast cancer prevention

The evidence here is pretty clear and consistent.

One good example is the 2008 study that found women averaging one cup of soymilk or about one-half cup of tofu daily have about 30% less risk of developing breast cancer, compared with women who have little or no soy products in their diets.

Reference : Wu AH, Yu MC, Tseng CC, Pike MC. Epidemiology of soy exposures and breast cancer risk. Br J Cancer. 2008;98:9-14.


However, even more compelling was the major review published By Messina and colleagues. I consider this to be one of the very the best review articles on this topic and well worth reading if you want more detail, even though it as written before research was published that examined the link between soy consumption and breast cancer outcomes (that comes next).

To quote:
The conclusion drawn from this extensive review of the available literature is that currently there is little evidence to suggest that any potential weak estrogenic effects of dietary isoflavones have a clinically relevant impact on breast tissue in healthy women. Limited data suggest this is also the case for breast cancer survivors.


This evidence includes multiple trials showing no effects on breast proliferation or mammographic density and considerable epidemiologic data showing either no effect or a modest protective role of soy/isoflavone intake on breast cancer risk.


Based on this evidence it seems unlikely that isoflavone consumption at dietary levels (i.e. <100 mg/day) elicits adverse breast cancer-promoting effects in healthy women or breast cancer survivors not undergoing active treatment.

Reference : Messina MJ and Wood CE; Nutrition Journal 2008.

The importance of an early habit

However, there is good evidence to suggest that to be fully effective in regards to prevention, the soy consumption may have to occur early in life - as breast tissue is forming during adolescence. It seems for adolescent girls, eating soy products may be very helpful.

Reference 1 : Korde LA, Wu AH, Fears T, et al. Childhood soy intake and breast cancer risk in Asian American women. Cancer Epidemiol Biomarkers Prev. 2009;18:1050-1059.
4.

Reference 2 : Shu XO, Jin F, Dai Q, et al. Soyfood intake during adolescence and subsequent risk of breast cancer among Chinese women. Cancer Epidemiol Biomarkers Prev. 2001;10:483-488.

Soy and breast cancer treatment
If something reduces your risk of a cancer recurrence by 25%, that sounds like a treatment to me. In my view it is very clear - nutrition is therapeutic for people with cancer generally and for women with breast cancer specifically. There is a good deal of strong science to support this proposition.

Here is a good research example from the not too distant past

A 2012 analysis that combined the results of prior studies and included a total of 9,514 women from the United States and China, concluded that women who consumed the most soy products were 25% less likely to have their cancer return, compared with those who tended to avoid soy products.

Reference : Nechuta SJ, Caan BJ, Chen WY, et al. 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. Am J Clin Nutr. 2012;96:123-132.

Now for the latest
An editorial published this month in the prestigious journal Cancer has this to say :
Recent data from Asia and North America indicate that soy foods may decrease the risk of breast cancer and improve the results of treatment in patients with breast cancer. Studying soy foods and isoflavones promises to be an exceptionally fertile area for a wide range of cancer researchers.

Reference : Cancer Journal editorial
Omer Kucuk MD, Soy foods, isoflavones, and breast cancer Cancer; 6 March 2017
DOI: 10.1002/cncr.30614

The editorial introduces findings from a new, long term study that confirms that women with breast cancer who consume soy products experience improved survival rates.

This study examined 6,235 women with breast cancer and monitored their diet records and mortality rates. Women with hormone-receptor-negative tumors who consumed the highest amounts of isoflavones from soy reduced their all-cause mortality by an average of 21% over the course of 9.4 years, compared with those who consumed the least amount.

It is significant that in this study, the lower mortality associated with higher intake was limited to women who had tumors that were negative for hormone receptors – where the reduction in risk of dying was an amazing 50%; and those who did not receive hormone therapy for their breast cancer – where the reduction was 32%.

Reference
Zhang FF, et al. Dietary isoflavone intake and all-cause mortality in breast cancer survivors: the Breast Cancer Family Registry. Cancer. Published online March 6, 2017.

Why do soy products reduce cancer risk? 

Most research has focused on the phytoestrogens found in soybeans.

Some researchers have suggested that these compounds somehow block the effects of women’s natural oestrogens and I explained this hypothesis in detail in the earlier blog posts.

However, that does not appear to be the entire explanation, as diet effects may also benefit people with oestrogen-receptor-negative cancers.


RELATED BLOGS
Is soy safe? - 1

Is soy safe? – 2

NEXT CANCER RESIDENTIAL PROGRAM

April 24 – 28th Cancer and Beyond

For many people these days, living with cancer is an ongoing reality. So how to do that? How to live fully and well in the potential shadow of a major illness?

It seems to me to be virtually essential to regularly take time out, to stand back, to re-assess, to keep on track, to get back on track when necessary, to clarify the confusion that is so easy to get into with all that is in the Press and on the net, and to perhaps most importantly, to be re-inspired and re- enthused for the journey ahead.

FULL DETAILS Click here