Soy and Breast Cancer

Written by Dr. Steve Chaney on . Posted in current health articles, Food and Health, Nutritiion

soy and breast cancerThe Soy Controversy

Author: Dr. Stephen Chaney

 

 

Soy and breast cancer: the wars are heating up again. You may have seen the recent headlines saying: “Soy protein found to speed the growth of breast cancer!” “Eating soy may turn on genes linked to [breast] cancer growth!” “Women with breast cancer should avoid high soy diets!” It all sounds pretty scary.

If this is true, it is big news. In recent years the consensus in the scientific community has been that soy is not harmful for women with breast cancer, and that it might even be beneficial. However, some skeptics have never accepted that consensus view. Those skeptics are once again claiming that soy protein may be risky for women with breast cancer.

Let’s look at the study behind the recent headlines and see if it is compelling enough to challenge the prevailing consensus on the safety of soy for women with breast cancer.

Does Soy Protein Turn On Breast Cancer Growth Genes?

This study (Shike et al, Journal of the National Cancer Institute, Sep 4 2014, doi: 10.1093/jnci/dju 189) looked at 140 women (average age 56) with invasive breast cancer. They were randomly divided into two groups of 70 and either given soy protein or a placebo between the initial biopsy and the time that surgery was performed to remove the tumor (a period of 7 to 30 days). A second biopsy was obtained at the time of surgery.

The activity of a number of genes associated with breast cancer survival was measured in the two biopsy samples. The observation that made the headlines was:

  • For some of the women in the study the activity of several genes associated with breast cancer growth and survival was increased in the group consuming soy protein compared to the placebo group. The authors concluded: “These data raise concern that soy may exert a stimulatory effect on breast cancer in a subset of women.”

What Are The Limitations Of The Study?

The authors acknowledged the many limitations of the study, but the press has largely ignored them.

  • The increased activity of the cancer growth genes was only seen in 20% of the women studied. For 80% of the women studied soy protein consumption had no effect on the activity of genes associated with breast cancer growth and survival.
  • This effect was only seen for some of the genes associated with breast cancer growth and survival. Other breast cancer growth genes were not affected in any of the women enrolled in the study. The authors conceded that it was unknown whether these limited genetic changes would have any effect on tumor growth and survival.
  • There was no effect of soy consumption on actual tumor growth in any of the women studied.
  • This was a very short term study so it is not known whether these changes in gene expression would have continued if soy supplementation were continued for a longer period of time. There are numerous examples in the literature of initial changes in gene expression in response to a radical change in diet that disappear once the body becomes accustomed to the new diet.
  • There is absolutely no way of knowing if the observed changes in gene expression would actually affect clinical outcomes such as survival, response to chemotherapy or tumor recurrence.

Should Women With Breast Cancer Avoid Soy?breast cancer prevention

Even with all of the limitations listed above, if this were the only study to test the soy-breast cancer hypothesis, I and most other experts would probably be warning women with breast cancer to be very cautious about consuming soy.

However, as I discussed in a previous “Health Tips From the Professor” (https://healthtipsfromtheprofessor.com/soy-and-breast-cancer-recurrence/) at least five clinical studies have been published on the effects of soy consumption on the recurrence of breast cancer in women who are breast cancer survivors, both in Chinese and American populations. 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 by breast cancer survivors.

A meta-analysis of all 5 studies was published last 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.

Another meta-analysis of 18 clinical studies found that soy slightly decreases the risk of developing breast cancer in the first place (J Natl Cancer Inst, 98: 459-471, 2006). To date there is absolutely no clinical evidence that soy increases the risk of breast cancer.

The Bottom Line

What does this mean for you if you are a woman with breast cancer, a breast cancer survivor or someone who is concerned about your risk of developing breast cancer?

  1. The study that has generated the recent headlines has so many limitations that I would not recommend any changes in soy consumption at present. It raises an interesting hypothesis that requires further study and validation. If this hypothesis holds up it may result in changes in dietary recommendations for a very small subset of women with invasive breast cancer.
  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.
  1. I personally feel that these studies are clear cut enough that women who are concerned about their breast cancer risk, women with breast cancer, and breast cancer survivors no longer need to fear soy protein as part of a healthy diet.
  1. 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.
  1. The irresponsible websites (I won’t name names, but you know who they are) are still warning breast cancer survivors to avoid soy completely. They are citing the latest study, with all of its limitations, as proof that they were right all along. As a scientist I really have a problem with people who are unwilling to change their opinions in the face of overwhelming scientific evidence to the contrary.
  1. 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.

 

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.

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Comments (2)

  • Amy Williams

    |

    Hi Steve, I sure have missed seeing you and Suzanne. I am enjoying reading and listening to your information

    Reply

    • Dr. Steve Chaney

      |

      We hope to see you soon. You are a good friend.

      Reply

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Latest Article

Can Plant-based Diets Be Unhealthy?

Posted September 10, 2019 by Dr. Steve Chaney

Do Plant-Based Diets Reduce Heart Disease Deaths?

Author: Dr. Stephen Chaney

 

plant-based diets vegetablesPlant-based diets have become the “Golden Boys” of the diet world. They are the diets most often recommended by knowledgeable health and nutrition professionals. I’m not talking about all the “Dr. Strangeloves” who pitch weird diets in books and the internet. I am talking legitimate experts who have spent their life studying the impact of nutrition on our health.

Certainly, there is an overwhelming body of evidence supporting the claim that plant-based diets are healthy. Going on a plant-based diet can help you lower blood pressure, inflammation, cholesterol and triglycerides. People who consume a plant-based diet for a lifetime weigh less and have decreased risk of heart disease, diabetes, and cancer.

But, can a plant-based diet be unhealthy? Some people consider a plant-based diet to simply be the absence of meat and other animal foods. Is just replacing animal foods with plant-based foods enough to make a diet healthy?

Maybe not. After all, sugar and white flour are plant-based food ingredients. Fake meats of all kinds abound in our grocery stores. Some are very wholesome, but others are little more than vegetarian junk food. If you replace animal foods with plant-based sweets, desserts, and junk food, is your diet really healthier?

While the answer to that question seems obvious, very few studies have asked that question. Most studies on the benefits of plant-based diets have compared population groups that eat a strictly plant-based diet (Seventh-Day Adventists, vegans, or vegetarians) with the general public. They have not looked at variations in plant food consumption within the general public. Nor have they compared people who consume healthy and unhealthy plant foods.

This study (H Kim et al, Journal of the American Heart Association, 8:e012865, 2019) was designed to fill that void.

 

How Was The Study Done?

plant-based diets studyThis study used data collected from 12,168 middle aged adults in the ARIC (Atherosclerosis Risk in Communities) study between 1987 and 2016.

The participant’s usual intake of foods and beverages was assessed by trained interviewers using a food frequency questionnaire at the time of entry into the study and again 6 years later.

Participants were asked to indicate the frequency with which they consumed 66 foods and beverages of a defined serving size in the previous year. Visual guides were provided to help participants estimate portion sizes.

The participant’s adherence to a plant-based diet was assessed using four different well-established plant-based diet scores. For the sake of simplicity, I will include 3 of them in this review.

  • The PDI (Plant-Based Diet Index) categorizes foods as either plant foods or animal foods. A high PDI score means that the participant’s diet contains more plant foods than animal foods. A low PDI score means the participant’s diet contains more animal foods than plant foods.
  • The hPDI (healthy plant-based diet index) is based on the PDI but emphasizes “healthy” plant foods. A high hPDI score means that the participant’s diet is high in healthy plant foods (whole grains, fruits, vegetables, nuts, legumes, coffee and tea) and low in animal foods.
  • The uPDI (unhealthy plant-based diet index) is based on the PDI but emphasizes “unhealthy” plant foods. A high uPDI score means that the participant’s diet is high in unhealthy plant foods (refined grains, fruit juices, French fries and chips, sugar sweetened and artificially sweetened beverages, sweets and desserts) and low in animal foods.

For statistical analysis the scores from the various plant-based diet indices were divided into 5 equal groups. In each case, the group with the highest score consumed the most plant foods and least animal foods. The group with the lowest score consumed the least plant foods and the most animal foods.

The health outcomes measured in this study were heart disease events, heart disease deaths, and all-cause deaths. Again, for the sake of simplicity, I will only include 2 of these outcomes (heart disease deaths and all-cause deaths) in this review. The data on deaths were obtained from state death records and the National Death Index. (Yes, your personal information is available on the web even after you die.)

 

Do Plant-Based Diets Reduce Heart Disease Deaths?

plant-based diets reduce heart deathsThe participants in this study were followed for an average of 25 years.

The investigators looked at heart disease deaths over the 25 years and compared people with the highest intake of plant foods to people with the highest intake of red meat and other animal foods. The results were:

  • People with the highest intake of plant foods and the highest intake of healthy plant foods (whole grains, fruits, vegetables, nuts, legumes, coffee and tea) had a 19-32% lower risk of dying from heart disease than people with the highest intake of red meat and other animal foods.
  • People with the highest intake of unhealthy plant foods (refined grains, fruit juices, French fries and chips, sugar sweetened and artificially sweetened beverages, sweets and desserts) had the same risk of dying from heart disease as people with the highest intake of red meat and other animal foods.

When the investigators looked at all-cause deaths over the 25 years:

  • People with the highest intake of plant foods and the highest intake of healthy plant foods had an 11-25% lower risk of dying from any cause than people with the highest intake of red meat and other animal foods.
  • People with the highest intake of unhealthy plant foods had the same risk of dying from heart disease as people with the highest intake of red meat and other animal foods.

What Else Did The Study Show?

The investigators made a couple of other interesting observations:

  • The association of the overall diet with heart disease and all-cause deaths was stronger than the association of individual food components. This underscores the importance of looking at the effect of the whole diet on health outcomes rather than the “magic” foods you hear about on Dr. Strangelove’s Health Blog.
  • Diets with the highest amount of healthy plant foods were associated with higher intake of carbohydrates, plant protein, fiber, and micronutrients, including potassium, magnesium, iron, vitamin A, vitamin C, folate, and lower intake of saturated fat and cholesterol.
  • Diets with the highest amount of unhealthy plant foods were associated with higher intake of calories and carbohydrates and lower intake of fiber and micronutrients.

The last two observations may help explain some of the health benefits of plant-based diets.

 

Can Plant-Based Diets Be Unhealthy?

plant-based diets unhealthy cookiesNow, let’s return to the question I asked at the beginning of this article: “Can plant-based diets be unhealthy?” Although some previous studies have suggested that unhealthy plant-based diets might increase the risk of heart disease, this study did not show that.

What this study did show was that an unhealthy plant-based diet was no better for you than a diet containing lots of red meat and other animal foods.

If this were the only conclusion from this study, it might be considered a neutral result. However, this result clearly contrasts with the data from this study and many others showing that both plant-based diets in general and healthy plant-based diets reduce the risk of heart disease deaths and all-cause deaths compared to animal-based diets.

The main message from this study is clear.

  • Replacing red meat and other animal foods with plant foods can be a healthier choice, but only if they are whole, minimally processed plant foods like whole grains, fruits, vegetables, nuts, legumes, coffee and tea.
  • If the plant foods are refined grains, fruit juices, French fries and chips, sugar sweetened and artificially sweetened beverages, sweets and desserts, all bets are off. You may be just as unhealthy as if you kept eating a diet high in red meat and other animal foods.

There is one other subtle message from this study. This study did not compare vegans with the general public. Everyone in the study was the general public. Nobody in the study was consuming a 100% plant-based diet.

For example:

  • The group with the highest intake of plant foods consumed 9 servings per day of plant foods and 3.6 servings per day of animal foods.
  • The group with the lowest intake of plant foods consumed 5.4 servings per day of plant foods and 5.6 servings per day of animal foods.

In other words, you don’t need to be a vegan purist to experience health benefits from adding more whole, minimally processed plant foods to your diet.

 

The Bottom Line

A recent study analyzed the effect of consuming plant foods on heart disease deaths and all-cause deaths over a 25-year period.

When the investigators looked at heart disease deaths over the 25 years:

  • People with the highest intake of plant foods and the highest intake of healthy plant foods had a 19-32% lower risk of dying from heart disease than people with the highest intake of red meat and other animal foods.
  • People with the highest intake of unhealthy plant foods had the same risk of dying from heart disease as people with the highest intake of red meat and other animal foods.

When the investigators looked at all-cause deaths over the 25 years:

  • People with the highest intake of plant foods and the highest intake of healthy plant foods had an 11-25% lower risk of dying from any cause than people with the highest intake of red meat and other animal foods.
  • People with the highest intake of unhealthy plant foods had the same risk of dying from heart disease as people with the highest intake of red meat and other animal foods.

The main message from this study is clear.

  • Replacing red meat and other animal foods with plant foods can be a healthier choice, but only if they are whole, minimally processed plant foods like whole grains, fruits, vegetables, nuts, legumes, coffee and tea.
  • If the plant foods are refined grains, fruit juices, French fries and chips, sugar sweetened and artificially sweetened beverages, sweets and desserts, all bets are off. You may be just as unhealthy as if you kept eating a diet high in red meat and other animal foods.

A more subtle message from the study is that you don’t need to be a vegan purist to experience health benefits from adding more whole, minimally processed plant foods to your diet. The people in this study were not following some special diet. The only difference was that some of the people in this study ate more plant foods and others more animal foods.

For more details on the study, 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.

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