Soy and Breast Cancer Archives - Health Tips From The Professor

The Estrogenic Myth

April 29, 2025 by Dr. Steve Chaney

What Does Increase Breast Cancer Risk?

Author: Dr. Stephen Chaney

It seems like every time you turn around there are new headlines warning us that a particular food or supplement increases your risk of cancer. If you believe all those headlines, there would be little you could eat. You might starve to death trying to avoid eating anything that increases your risk of cancer.

So, it’s important to ask which of those warnings are true and which are just myths.

For example, a few days ago, a friend called me and said, “I just heard that resveratrol is estrogenic and causes breast cancer. Should I read the labels of the herbal supplements I take and avoid anything with resveratrol in it.”

I assured her that this was just a myth. The likelihood that resveratrol and related polyphenols cause breast cancer is very low. And if she was concerned about breast cancer, there were much more important things to worry about.

But as I started to explain why it was a myth, I realized the explanation was complex. I was able to explain it to my friend in a 20-minute discussion. But it was then I realized I needed to write a “Health Tips From the Professor” article to help explain it to the general public.

Why Are We Concerned?

You might be asking, “Why is this such a big deal? Why do we care if something has estrogenic properties?” Let me start at the beginning.

When I first started teaching medical students in 1972, hormone replacement therapy (a combination of estrogen and progesterone) was thought to be a safe and effective treatment for menopausal symptoms and post-menopausal bone loss, and it was very widely prescribed.

That practice came to a screeching halt in 2002 when the Woman’s Health Initiative study showed that it increased the risk of breast, endometrial, and ovarian cancer. Today,

The hormone composition of hormone replacement therapy has been changed.

It is only prescribed for severe menopausal symptoms. And drugs are the treatment of choice to reduce post-menopausal bone loss.

It is prescribed for the shortest possible time to limit exposure.

These simple changes in hormone replacement therapy represent the single most important intervention for reducing breast cancer risk in the past 50 years. Yes, you heard that right. These changes were more effective than any other medication or preventative strategy for reducing the number of women developing and dying from breast cancer.

This lesson made a big impression on the medical community. So, it is easy to understand why anything resembling estrogen is immediately suspected of increasing the risk of breast cancer. But the reality is far more complicated. So, it’s time for another of my “Biochemistry 101” segments.

Biochemistry 101: What Does Estrogenic Mean?

Let’s start at the beginning with what polyphenols are. They comprise a diverse group of compounds with these common features.

If you look at their structures, they contain multiple rings (A chemist would tell you they have more than one phenol group, hence the term polyphenol. But that terminology is only useful if you are a chemist).

They are found in plants. Specifically, they are found in fruits, vegetables, herbs, spices and beverages (coffee, tea, and cocoa, for example).

They have antioxidant properties.

Types of polyphenols include flavonoids, phenolic acids, lignans, and stilbenes. I mention this only because soy isoflavones, which I will talk about later, are flavonoids.

Some of these compounds have structures that resemble estrogen. If they bind to estrogen receptors and have the same effect as estrogen in cultured human cells, they are said to have “estrogenic properties”.

That’s why you see blogs warning about foods and herbal ingredients we should avoid because of their “estrogenic” properties. Some of these blogs are written by people with “Dr” on front of their name. But they aren’t biochemists and don’t know what biochemists know.

Let’s dig a little deeper. Here are some of the complexities that most bloggers either don’t know about or ignore.

There is more than one kind of estrogen receptor.

Different estrogen receptors have different effects in the cell. For example, some estrogen receptors activate pathways that increase cancer risk. Other receptors activate pathways that decrease cancer risk.

The same estrogen receptor can have different effects in different cell types. That’s why estrogen replacement therapy reduced menopausal symptoms and post-menopausal bone loss AND increased cancer risk in other tissues.

The Estrogenic Myth

A couple of weeks ago I talked about “The Soy Myth”, specifically the myth that soy isoflavones increase breast cancer risk. Of course, that myth was based on the observation that soy isoflavones have estrogenic properties and a simplistic interpretation of what that means. But in fact, soy isoflavones:

Are found naturally in most soy foods unless they are highly processed.

Bind strongly to the estrogen receptors that decrease cancer risk.

Bind weakly to the estrogen receptors that increase breast cancer risk.

In contrast, estrogen:

Binds strongly to the estrogen receptors that increase breast cancer risk.

Binds weakly to the estrogen receptors that decrease breast cancer risk.

Soy isoflavones compete with estrogen for binding to the receptors that increase breast cancer risks. This helps protect breast cells from the cancer-promoting effects of estrogen.

So, it is true that soy isoflavones bind to estrogen receptors, but on the balance, you would predict that soy isoflavones decrease, rather than increase breast cancer risk.

The key word here is “predict” breast cancer risk. If you are a woman, you don’t want a prediction, you want to know one way or the other.

That’s why multiple human clinical studies have been conducted to determine the effect of soy foods on breast cancer risk. As I told you two weeks ago:

Some studies showed no effect of soy consumption on the risk of getting breast cancer or breast cancer recurrence if you have previously had breast cancer.

Other studies found that soy consumption reduced the risk of breast cancer occurrence and recurrence.

No studies found that soy consumption increased the risk of breast cancer occurrence or recurrence.

So, for soy the answers are clear.

Yes, soy isoflavones have estrogenic properties.

No, soy consumption is not associated with an increased risk of breast cancer. That is a myth.

The situation with resveratrol is similar:

It is found naturally in grapes and many other fruits.

It has estrogenic properties.

Cell culture experiments show that it activates pathways that reduce cancer risk.

Animal studies predominantly show that it reduces cancer risk. The only exceptions are a few animal studies with very high doses of resveratrol.

The few clinical studies that have been done show that it either has no effect on breast cancer risk or reduces cancer risk.

No human clinical trials have shown that resveratrol increases cancer risk.

The take home lesson is clear. Knowing that a food or herbal ingredient has estrogenic properties is meaningless unless you have data from human clinical trials on cancer outcomes.

So, the next time you see headlines telling you that you should avoid a food or herbal ingredient because it has “estrogenic properties” treat them skeptically. Unless the claim is backed up by human clinical trials showing an increased cancer risk, the claim is probably a myth.

What Does Increase Breast Cancer Risk?

The take home lesson is clear. If you are concerned about your risk of breast cancer or any other form of cancer you should ignore the social media posts, podcasts, and blogs about the cancer risks of estrogenic foods and herbal ingredients.

Unless they are backed by human clinical trials showing they increase cancer risks, the claims are likely to be mythical rather than real.

If they have any effect on cancer risk, it is likely to be small. Instead, focus on the important risk factors.

According to the American Cancer Society, the top 5 risk factor for breast cancer, and most other cancers, are:

#1: Overweight and obesity. The American Cancer Society recommends that you get and stay at a healthy weight.

Let me put this in perspective for you. Even if things like soy and resveratrol increased your risk of breast cancer, their effect is very small compared to estrogen and you are only exposed to them briefly once or twice a day.

In contrast, fat cells produce estrogen, and if you are overweight, fat cells accumulate in your breasts. Those fat cells are bathing your breast cells in a bath of pure estrogen 24/7.

#2: Inactivity. The American Cancer Society recommends that adults get at least 150 to 300 minutes of moderate intensity or 75 to 150 minutes of vigorous intensity activity each week (or a combination of these), preferably spread throughout the week.

#3: Alcohol use. The American Cancer Society says it is best not to drink alcohol at all. For women who do drink, they should have no more than 1 alcoholic drink a day.

#4: Hormone use after menopause. The American Cancer Society recommends talking to your health care provider about non-hormonal options to treat menopausal symptoms.

#5: Poor diet. The American Cancer Society recommends a diet low in fat, processed and red meat, and sugary drinks, but high in fruits and vegetables.

The Bottom Line

It seems like every day you hear about another food or supplement you should avoid because it has “estrogenic properties” and is likely to cause cancer. I call this the estrogenic myth because those claims are generally mythological rather than factual. In this article:

I discuss why these claims are myths rather than facts using soy isoflavones and resveratrol as examples.

Tell you what the American Cancer Society tells you to focus on if you want to decrease your risk of breast cancer and other cancers.

For more details on these studies and what they mean for you, read the article above.

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.

____________________________________________________________________________

My posts and “Health Tips From the Professor” articles carefully avoid claims about any brand of supplement or manufacturer of supplements. However, I am often asked by representatives of supplement companies if they can share them with their customers.

My answer is, “Yes, as long as you share only the article without any additions or alterations. In particular, you should avoid adding any mention of your company or your company’s products. If you were to do that, you could be making what the FTC and FDA consider a “misleading health claim” that could result in legal action against you and the company you represent.

For more detail about FTC regulations for health claims, see this link.

https://www.ftc.gov/business-guidance/resources/health-products-compliance-guidance

_____________________________________________________________________

About The Author

Dr. Chaney has a BS in Chemistry from Duke University and a PhD in Biochemistry from UCLA. He is Professor Emeritus from the University of North Carolina where he taught biochemistry and nutrition to medical and dental 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 textbooks for medical students.

Since retiring from the University of North Carolina, he has been writing a weekly health blog called “Health Tips From the Professor”. He has also written two best-selling books, “Slaying the Food Myths” and “Slaying the Supplement Myths”. And most recently he has created an online lifestyle change course, “Create Your Personal Health Zone”. For more information visit https://chaneyhealth.com.

For the past 53 years Dr. Chaney and his wife Suzanne have been helping people improve their health holistically through a combination of good diet, exercise, weight control and appropriate supplementation.

The Soy Myth

April 15, 2025 by Dr. Steve Chaney

Why Is There So Much Confusion About Soy?

Author: Dr. Stephen Chaney

What is the truth about soy and breast cancer? Does it increase the risk of breast cancer, or is that just a myth? 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 increases 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” has been 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? 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 Most Recent Study Show?

In earlier 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 established 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 Soy Myth

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 most recent 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.

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

For more information on this study and other things you can do to reduce the risk of breast cancer read the article above.

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.

______________________________________________________________________________

For more detail about FTC regulations for health claims, see this link.

https://www.ftc.gov/business-guidance/resources/health-products-compliance-guidance

_______________________________________________________________________

About The Author

The Truth About Soy And Breast Cancer

May 24, 2022 by Dr. Steve Chaney

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.

Why Is There So Much Confusion About Soy?

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.

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.

What Have Previous Clinical Studies Shown?

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.

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.

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.”

The Truth About Soy And Breast Cancer

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.

Soy And Breast Cancer Survivors

February 5, 2019 by Dr. Steve Chaney

Do Soy & Cruciferous Vegetables Reduce Breast Cancer Treatment-Related Symptoms?

Author: Dr. Stephen Chaney

The topic of soy and breast cancer has been a controversial subject for years. If you read Dr. Strangelove’s nutrition blogs, you would be led to believe that soy causes breast cancer and shortens the lifespan of breast cancer survivors.

This is one of the many myths I have debunked in my book “Slaying The Supplement Myths.” Multiple clinical studies have proven that soy reduces the likelihood of developing breast cancer. Several clinical studies have shown it also decreases recurrence of breast cancer and enhances survival following breast cancer treatment. Other clinical studies have found no effect of soy on recurrence or longevity in breast cancer survivors. Zero studies have found any detrimental effects of soy in breast cancer survivors.

So, is there a true relationship between soy and breast cancer survivors? These studies have all shown that soy is part of a healthy diet and should not be feared by women who have survived breast cancer.

Breast cancer survivors suffer from several treatment-related side effects. These include menopausal symptoms, fatigue, joint problems, hair thinning, and memory loss.

The most recent headlines claim that soy and cruciferous vegetables (broccoli, cauliflower, cabbage, Brussels sprouts, kale and related vegetables) decrease menopause and other treatment-related symptoms in breast cancer survivors. If you have seen those headlines, you are probably wondering:

Are they true?
Should I increase soy consumption following breast cancer treatment?

How Was The Study Designed?

This study (SJO Nomura et al, Breast Cancer Research and Treatment, 168: 467-479) enrolled 192 Chinese-American and 173 non-Hispanic White women in the San Francisco Bay area between 2006 and 2012. The average age of the women was 57. They were all breast cancer survivors who had been treated 1-5 years previously. Most had been treated at least 2 years previously.

The participants were recruited by mail and filled out questionnaires which provided demographic data, health information, and information on treatment-related symptoms. They also filled out a food frequency questionnaire designed to estimate intake of soy foods and cruciferous vegetables.

In terms of food consumption, the range was:

0 to 24 gram/day for soy.
<33 grams/day to >71 grams/day for cruciferous vegetables. For reference, one serving (1/2 cup) of cooked broccoli weighs 78 grams.

Soy And Breast Cancer Survivors?

In looking at the effect of soy and cruciferous vegetables on treatment-related symptoms, it is important to understand that the two groups of women had different baseline characteristics.

The Chinese-American women had a higher average intake of both soy and cruciferous vegetables.
The Non-Hispanic White women were more likely to experience treatment-related worsening of menopausal symptoms.
The Chinese-American women were more likely to experience fatigue, joint problems, hair thinning, and memory loss.

With that in mind, here are the results of the study:

Soy intake:

When all women in the study were grouped together, high (>24 grams/day) versus low (0 grams/day) soy intake was associated with a 57% reduction in fatigue.
For Non-Hispanic White women high versus low soy intake was associated with a 71% reduction in menopause symptoms and a 75% reduction in fatigue.
The effect of soy on treatment-related symptoms was non-significant for Chinese-American women, perhaps because the baseline intake of soy was greater for this group.

Cruciferous vegetable intake:

When all women in the study were grouped together, high (>71 grams/day) versus low (<33 grams/day) cruciferous vegetable intake was associated with a 50% reduction in menopause symptoms.
For Chinese-American women, high versus low intake of cruciferous vegetables was associated with a 39% reduction in memory loss.
The effect of cruciferous vegetables on treatment-related symptoms was non-significant for Non-Hispanic White women.

The authors concluded: “In this population of breast cancer survivors, higher soy and cruciferous vegetable intake was associated with less treatment-related menopausal symptoms and fatigue. To confirm study findings, additional research is needed that explores the relationship between diet and breast cancer treatment-related symptoms…in a larger, diverse study population.”

What Does This Study Mean For You?

This is a small, preliminary study that needs to be repeated before any definitive recommendations can be made. Here are my take-home points from this study.

Soy is an excellent source of high-quality plant protein. We already know there is no reason to avoid soy following breast cancer treatment. This study provides another reason to include soy as part of a healthy, plant-based diet following treatment. This study also provides a rationale for including cruciferous vegetables as part of a healthy, plant-based diet following treatment.
However, 24 grams of soy represents a single serving of many soy foods. This study does not provide a rationale to increase soy consumption beyond a single serving.
The danger after studies like this are publicized is that breast cancer survivors will just focus on soy and cruciferous vegetables in their diet. This study looked at the effects of soy and cruciferous vegetables based on their potential effects on menopausal symptoms. However, they are just two components of a healthy, plant-based diet, and we know that primarily plant-based diets are associated with a decreased risk of breast cancer.

In my opinion, we need to focus less on “magic bullet” approaches (single nutrients and single foods) and focus more on holistic approaches. We should be asking how holistic, healthy diets influence recovery from breast cancer and reduction of treatment-related symptoms. We should be encouraging breast cancer survivors to focus on all aspects of a healthy diet, not just soy and cruciferous vegetables.

The Bottom Line

This is one of the many myths I have debunked in my book “Slaying The Supplement Myths.” Multiple clinical studies have shown that soy is part of a healthy diet and should not be feared by women who have survived breast cancer.

The most recent headlines claim that soy and cruciferous vegetables (broccoli, cauliflower, cabbage, Brussels sprouts, kale and related vegetables) decrease menopause symptoms and fatigue in breast cancer survivors.

These headlines are based on a small, preliminary study that needs to be repeated before any definitive recommendations can be made. Here are my take-home points from this study.

Soy is an excellent source of high-quality plant protein. We already know there is no reason to avoid soy following breast cancer treatment. This study provides another reason to include soy as part of a healthy, plant-based diet following treatment. This study also provides a rationale for including cruciferous vegetables as part of a healthy, plant-based diet following treatment.
However, 24 grams of soy represents a single serving of many soy foods. This study does not provide a rationale for increasing soy consumption beyond a single serving.
This study focused on soy and cruciferous vegetables based on their potential effects on menopausal symptoms. However, they are just two components of a healthy, plant-based diet, and we know that primarily plant-based diets are associated with a decreased risk of breast cancer. In my opinion, we need to focus less on “magic bullet” approaches (single nutrients and single foods) and focus more on holistic approaches. We should be asking how healthy diets influence recovery from breast cancer and reduction of treatment-related symptoms.

For more details read the article above.

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.

Does Soy Increase Breast Cancer Risk?

May 2, 2017 by Dr. Steve Chaney

What Does the Latest Study Say?

Author: Dr. Stephen Chaney

Does soy increase breast cancer risk?

“To soy or not to soy. That is the question.” 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.

Why Is There So Much Confusion About Soy?

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.

The confusion has been amplified by claims and counter-claims 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 claimed that soy definitely increased breast cancer risk and should be avoided at all cost. Their claims were picked up by other web sites. Eventually, the claims were 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.

It is easy to see why the general public still asks “Does soy increase breast cancer risk?”

What Have Previous Clinical Studies Shown?

The question “Does soy increased breast cancer risk” 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 Meta-Analysis-of-Soy-Intake-and-Breast-Cancer-Risk). 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 (soy-and-breast-cancer-recurrence) 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.

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

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 breast cancer. Therefore, we can recommend women to consume soy foods because of soy’s many health benefits.” In light of this study, has the question “Does soy increase breast cancer risk” been answered?

Does Soy Increase Breast Cancer Risk?

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

Does soy increase breast cancer risk? No.

The Bottom Line

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.
Multiple clinical studies have shown that soy either has no effect on breast cancer risk, or that it reduces the risk.
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.
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.
No clinical studies have provided any evidence to support the claim that soy increases either breast cancer risk or breast cancer recurrence.
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

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.