The Lies You’ve Been Told About Soy and Breast Cancer Recurrence

Written by Dr. Steve Chaney on 12 September 2014. Posted in Fitness Fridays, Health, Fitness & Wellness, Issues

The usual response when you are finding your way around an unfamiliar or confusing topic is to consult experts on the topic.You desire feedback and some sort of validation or resolutions for your concerns. After all, your concerns are legitimate and often any action or inaction on your part has potentially serious consequences.

The problem is that there is a lot of conflicting and downright incorrect information available. Shifting through the cacophony of voices clamouring for your attention can be intimidating. For example, if you’re concerned with the linkage between soy and breast cancer, it’s highly likely you’ve already come across some of these issues.

You’ve probably heard the warnings:

“Soy may increase the risk of breast cancer!”

“Women with breast cancer shouldn’t use soy!”

The first warning was never true. Numerous clinical studies have shown that consumption of soy protein is associated with a lower risk of developing breast cancer.

Furthermore, the science behind the second warning has never been very strong. The concerns that soy might stimulate the growth of breast cancer cells was based primarily on cell culture experiments and one experiment in mice – even though a second experiment in mice came to the exact opposite conclusion.

In fact, the definitive clinical studies have been performed, and it turns out for women who are breast cancer survivors, consumption of soy foods does not increase either the risk of breast cancer recurrence or of dying from breast cancer. The first of these studies was reported in the December 2009 issue of the Journal of the American Medical Association by researchers at Vanderbilt University and Shanghai Institute of Preventive Medicine (Shu et al, JAMA, 302: 2437-2443, 2009).

The results were clear cut. Breast cancer survivors with the highest soy intake had 25% less chance of breast cancer recurrence and 25% less chance of dying from breast cancer than the women with the lowest soy intake.

The effect was equally strong for women with estrogen receptor-positive and estrogen receptor- negative cancers, for early stage and late stage breast cancer and for pre- and post- menopausal women. In short this was a very robust study.

Other Clinical Studies

If that were the only published clinical study to test the soy-breast cancer hypothesis, I and other experts would be very cautious about making definitive statements. However, at least four more clinical studies have been published since then, both in Chinese and American populations. The studies have either shown no significant effect of soy on breast cancer recurrence or a protective effect. None of them have shown any detrimental effects of soy consumption by breast cancer survivors.

A meta-analysis of all 5 studies was published earlier this year (Chi et al, Asian Pac J Cancer Prev., 14: 2407-2412, 2013). This study combined the data from 11,206 breast cancer survivors in the US and China. Those with the highest soy consumption had a 23% decrease in recurrence and a 15% decrease in mortality from breast cancer.

The Bottom Line:

What does this mean for you if you are a breast cancer survivor?

1. There are many reasons to include soy protein foods as part of a healthy diet. Soy foods are one of the highest quality vegetable protein sources and provide a great alternative to many of the high fat, high cholesterol animal proteins in the American diet.

2. I personally feel that the published studies are clear cut enough that breast cancer survivors no longer need to fear soy protein as part of a healthy diet.

3. The responsible websites agree with this assessment. For example,WebMD and the American Institute for Cancer Research (AICR) both say that breast cancer survivors need no longer worry about eating moderate amounts of soy foods.

4. The irresponsible websites (I won’t name names, but you know who they are) are still warning breast cancer survivors to avoid soy completely. As a scientist I really have problem with people who are unwilling to change their opinions in the face of overwhelming scientific evidence to the contrary.

5. Finally, I want to emphasize that the published studies merely show that soy does not increase the risk of breast cancer and is safe to use for breast cancer survivors. None of those studies suggest that soy is an effective treatment for breast cancer. The protective effects of soy are modest at best. If you have breast cancer, consult with your physician about the best treatment options for you.

When determining which foods to eat, make sure to consult credible scientific sources. Be aware of the fact that there is lots of misinformation out there, some of it with an agenda to deliberately mislead. Doing your research pays off when eating healthy because you will come across real experts doing real research that you can use to guide you as you do your best to lead a healthy life. Remember, your well-being is much too important and fragile to trust to rumor and hearsay. Informing yourself will prove invaluable as you strive to be the healthiest you can.

**Edited for repurpose by Alex Kvaskov, Content Development Intern at Women Who Run It.

Dr. Steve Chaney

Dr. Chaney has a PhD in Biochemistry from UCLA. He is Professor Emeritus from the University of North Carolina where he taught biochemistry and nutrition to medical students for 40 years. Dr. Chaney won numerous teaching awards at UNC, including the Academy of Educators “Excellence in Teaching Lifetime Achievement Award”. Dr Chaney also ran an active cancer research program at UNC and published over 100 scientific articles and reviews in peer-reviewed scientific journals. In addition, he authored two chapters on nutrition in one of the leading biochemistry text books for medical students. He is currently editor in chief of www.healthtipsfromtheprofessor.com