Why Is There So Much Confusion About Soy?

Author: Dr. Stephen Chaney

What is the truth about soy and breast cancer? If you are a woman, particularly a woman with breast cancer, it is an important question.

Some experts say soy should be avoided at all costs. They say that soy will increase your risk of breast cancer. Other experts say soy is perfectly safe and may even reduce your risk of breast cancer. Who is right?

If you are a breast cancer survivor, the question of whether soy increases or decreases your risk of disease recurrence is even more crucial. You have already endured surgery, chemotherapy, and/or radiation. You never want to go through that again.

Why Is There So Much Confusion About Soy?

Soy isoflavones decrease estrogen production, strengthen the immune system, inhibit cell proliferation, and reduce the production of reactive oxygen species. These are all effects that might reduce breast cancer risk.

On the other hand, soy isoflavones also bind to estrogen receptors and exhibit weak estrogenic activity. This effect has the potential to increase breast cancer risk.

Cell culture and animal studies have only confused the issue. Soy isoflavones stimulate the growth of breast cancer cells in a petri dish. Soy isoflavones also stimulate breast cancer growth in a special strain of mice lacking an immune system. However, in studies in both mice and rats with a functioning immune system, soy isoflavones decrease breast cancer risk.

The confusion has been amplified by claims and counterclaims on the internet. There are bloggers who are more interested in the spectacular than they are in accuracy (Today we call this fake news). They have taken the very weak evidence that soy isoflavones could possibly increase breast cancer risk and have blown it all out of proportion.

Their blogs claim that soy definitely increase breast cancer risk and should be avoided at all costs. Their claims have been picked up by other web sites and blogs. Eventually, the claims have been repeated so many times that people started to believe them. A “myth” was created. I call it a myth because it was never based on convincing scientific evidence.

In the meantime, scientists looked at the cell culture and animal studies and took a more responsible approach. They said “If this is true, it is an important public health issue. We need to do clinical trials in humans to test this hypothesis.”

What Have Previous Clinical Studies Shown?

The question of whether soy consumption increased the risk of developing breast cancer was settled a long time ago. Some studies have shown no effect of soy consumption on breast cancer risk. Others have reported that soy consumption decreased breast cancer risk. A meta-analysis of 18 previous clinical studies found that soy slightly decreased the risk of developing breast cancer (J Natl Cancer Inst, 98: 459-471, 2006). None of those studies found any evidence that soy increased the risk of breast cancer.

What about recurrence of breast cancer in women who are breast cancer survivors? Between 2006 and 2013 there have been five major clinical studies looking at the effects of soy consumption on breast cancer recurrence in both Chinese and American populations. Once again, the studies have shown either no effect of soy on breast cancer recurrence or a protective effect. None of them have shown any detrimental effects of soy consumption for breast cancer survivors.

A meta-analysis of all 5 studies was published in 2013 (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.

What Did The Latest Study Show?

In previous clinical studies the protective effect of soy has been greater in Asian populations than in North American populations. This could have been because Asians consume more soy. However, it could be due to other population differences as well. To better evaluate the effect of soy consumption on breast cancer survivors in the North America, a group of investigators correlated soy consumption with all-cause mortality in breast cancer survivors in the US and Canada (Zhang et al, Cancer, DOI: 10.1002/cncr.30615, March 2017).

The data were collected from The Breast Cancer Family Registry, an international research infrastructure establish in 1995. The women enrolled in this registry either have been recently diagnosed with breast cancer or have a family history of breast cancer.

This study included 6235 breast cancer survivors from the registry who lived in the San Francisco Bay area and the province of Ontario in Canada. The women represented an ethnically diverse population and had a median age of 51.8 at enrollment. Soy consumption was assessed either at the time of enrollment or immediately following breast cancer diagnosis. The women were followed for 9.4 years, during which time 1224 of them died.

The results were as follows:

There was a 21% decrease in all-cause mortality for women who had the highest soy consumption compared to those with the lowest soy consumption.

- The protective effect of soy was strongest for those women who had receptor negative breast cancer. This is significant because receptor-negative breast cancer is associated with poorer survival rates than hormone receptor-positive cases.

- The protective effect was also greatest (35% reduction in all-cause mortality) for women with the highest soy consumption following breast cancer diagnosis. This suggests that soy may play an important role in breast cancer survival.

The authors concluded “In this large, ethnically diverse cohort of women with breast cancer, higher dietary intake of [soy] was associated with reduced total mortality.”

In an accompanying editorial, Omer Kucuk, MD, of the Winship Cancer Institute of Emory University, noted that the United States is the number 1 soy producer in the world and is in a great position to initiate changes in health policy by encouraging soy intake. He said “We now have evidence that soy foods not only prevent breast cancer but also benefit women who have had breast cancer. Therefore, we can recommend women to consume soy foods because of soy’s many health benefits.”

The Truth About Soy And Breast Cancer

Every clinical study has its limitations. If there were only one or two studies, the question of whether soy increases breast cancer risk might still be in doubt. However, multiple clinical studies have come to the same conclusion. Either soy has no effect on breast cancer risk and breast cancer recurrence, or it has a protective effect.

Not a single clinical study has found any evidence that soy increases breast cancer risk. It is clear that consumption of soy foods is safe, and may be beneficial, for women with breast cancer. The myth that soy increases breast cancer risk needs to be put to rest.

On the other hand, we should not think of soy as a miracle food. Breast cancer risk is also decreased by a diet that:

Contains lots of fruits and vegetables.
Is low in processed grains & sweets and high in whole grains.
Is low in saturated & trans fats and high in omega-3 and monounsaturated fats.
Is low in red & processed meats and high in beans, fish & chicken.

Furthermore, diet is just one component of a holistic approach for reducing the risk of breast cancer. In addition to a healthy diet, the American Cancer Society recommends that you:

Control your weight
Be physically active
Limit alcohol
Don’t smoke
Limit hormone replacement therapy unless absolutely necessary.
Reduce stress

The Bottom Line

1) It is time to put the myth that soy increases breast cancer risk to rest. This myth is based on cell culture and animal studies, and those studies were inconclusive.

2) Multiple clinical studies have shown that soy either has no effect on breast cancer risk, or that it reduces the risk.

3) Multiple clinical studies have also shown that soy either has no effect on breast cancer recurrence in women who are breast cancer survivors, or that it reduces recurrence.

4) The latest clinical study is fully consistent with previous studies. It reports:

- There was a 21% decrease in all-cause mortality for women who had the highest soy consumption compared to those with the lowest soy consumption.

- The protective effect of soy was strongest for those women who had receptor negative breast cancer. This is significant because receptor-negative breast cancer is associated with poorer survival rates than hormone receptor-positive cases.

- The protective effect was also greatest (35% reduction in all-cause mortality) for women with the highest soy consumption following breast cancer diagnosis. This suggests that soy may play an important role in breast cancer survival.

5) No clinical studies have provided any evidence to support the claim that soy increases either breast cancer risk or breast cancer recurrence.

6) On the other hand, we should not think of soy as a miracle food. Breast cancer risk is also decreased by a diet that:

- Contains lots of fruits and vegetables.
- Is low in processed grains & sweets and high in whole grains.
- Is low in saturated & trans fats and high in omega-3 and monounsaturated fats.
- Is low in red & processed meats and high in beans, fish & chicken

7) Finally, diet is just one component of a holistic approach for reducing the risk of breast cancer. In addition to a healthy diet, the American Cancer Society recommends that you:

- Control your weight
- Be physically active
- Limit alcohol
- Don’t smoke
- Limit hormone replacement therapy unless absolutely necessary.
- Reduce stress

These statements have not been evaluated by the Food and Drug Administration. This information is not intended to diagnose, treat, cure, or prevent any disease.

Can A Multivitamin A Day Keep Breast Cancer At Bay?

Author: Dr. Stephen Chaney

A few weeks ago I wrote about soy and breast cancer survival. You’ve probably seen the latest headlines: “Multivitamin Supplements May Reduce Breast Cancer Mortality” and are wondering if they could possibly be true. After all, wasn’t it just a short time ago that the headlines said “Multivitamin supplements have no effect on breast cancer mortality” or that “Multivitamins may increase your risk of death”?

With all the conflicting headlines, you have every right to be skeptical about the latest news. So perhaps we should start with looking at the previous studies and discussing why they disagree.

What do we know about multivitamin use and breast cancer survival?

Three very large studies have reported no correlation between multivitamin use and breast cancer incidence. So it is pretty clear that multivitamins don’t prevent breast cancer.

However, breast cancer incidence and breast cancer survival are two different things. In the first case you are starting with healthy women and asking how many of them develop cancer. That is what we scientists call a primary prevention study. It is very difficult to prove the effectiveness of any intervention in a primary prevention study. In the second case you are starting with a sick population and asking if an intervention provides a benefit. It is much easier to prove whether or not an intervention is effective in this kind of study.

There, have been several small studies looking at the effect of vitamin supplementation in women who already had breast cancer. While the results have been mixed, the majority of the studies showed that vitamin supplementation did appear to reduce breast cancer recurrence and mortality.

What makes this study different?

The women in this study were part of 161,608 women enrolled the Women’s Health Initiative (WHI) study to investigate the effects of multivitamin use in post-menopausal women. In fact, this was one of the studies to report no effect of multivitamin use on the incidence of breast cancer (Neuhouser et al, Arch. Intern. Med., 169: 294-304, 2009).

What the present study did was to look at the those women in the WHI who did develop breast cancer during the previous study and followed them for an additional 7.9 years to see if multivitamin use affected breast cancer survival (Wasserthiel-Smoller et al, Breast Cancer Res. Treat., 141: 495-505, 3013).

This is the largest study of its kind (7,728 women). It started with an older and sicker group of women than previous studies. All of the women were 50-79 years old at the time the study began, and all of them had invasive breast cancer at the time of enrollment into the study.

The results were quite impressive. Multivitamin use improved survival by 30%, and the results were highly significant.

Strengths of the Study:

This was a large and very well controlled study. The authors did an excellent job of controlling for confounding variables that might have affected the outcome.

Multivitamin use was measured at multiple time points. It was assessed at enrollment into the original WHI study and at each subsequent doctor visit. The multivitamin usage for the purpose of data analysis was the usage at the time of breast cancer diagnosis, but the authors also corrected for any change in vitamin use post-diagnosis.

The study was in agreement with the majority of previous studies, further strengthening the conclusion that multivitamin use in women with breast cancer improves the likelihood of survival.

Weaknesses of the Study:

Because previous studies have been mixed with respect to the effect of multivitamins on breast cancer survival, further placebo controlled intervention studies will be required before multivitamin use becomes part of the standard of treatment for breast cancer patients.

Most of the women in the study were post-menopausal. It is unclear if multivitamins will provide the same benefit to pre-menopausal women with breast cancer.

This study measured consistent multivitamin use before and after the diagnosis of breast cancer. It did not look at women who began multivitamin use after diagnosis. So we have no idea whether starting multivitamin use after diagnosis would have also been beneficial.

The Bottom Line:

1) This study strongly suggests that multivitamin use may help improve your chances of survival if you are unlucky enough to develop breast cancer. While more studies are still needed, this study certainly strengthens the argument for multivitamin use.

2) The rap on multivitamins has always been that they aren’t needed by healthy people who have a good diet. However, multivitamins are important for assuring good nutritional status if your diet is not optimal or if you have increased nutritional needs – either because of your genetic makeup or because of illness.

3) The difficulty is that you usually don’t know if your genetics increases your vitamin needs, and once your disease has progressed far enough to be diagnosed it may be too late to improve disease outcome. That’s why many experts consider a multivitamin supplement as an inexpensive form of nutritional and health insurance. I concur.

4) As for the fear that multivitamins might just kill you, that hypothesis has been disproven by several subsequent studies including one published just a couple of weeks ago (Macpherson et al, Am. J. Clin. Nutr., doi: 10.3945/ajcn.112.o49304).

These statements have not been evaluated by the Food and Drug Administration. This information is not intended to diagnose, treat, cure or prevent any disease.