Soy and Hormone Related Cancers

This article addresses a thoughtful question that was submitted by one of our readers. The reader had concerns about whether his wife, who was recently diagnosed with breast cancer, should include soy foods in her diet. We address this concern with a clear explanation of the science behind the confusing idea that "Soy foods are dangerous for women with breast cancer."

The concepts around soy foods, estrogen, and breast cancer often are presented in ways that are misleading and anxiety-producing for individuals who have been diagnosed with breast or other hormone related cancers such as ovarian or endometrial cancer. We feel that helping people to understand the science behind the various connections between soy foods in the diet and risk of cancer is the best way to relieve this anxiety and help people make wise nutrition choices. In this article, we discuss this topic and provide practical nutrition advice for how to handle soy in the diet if you have a history of breast or other hormone related cancers.

Note: Numbers appearing at the end of sentences indicate research references. References are listed at the end of each article.

Reader Question

"My wife has breast cancer. Her oncologist informed her not to have soy because it was estrogen producing and would stimulate cancer growth. In all of the information I have read, I cannot find supportive facts for this statement. On the contrary, I have found information stating that it does not produce harmful estrogen and may actually reduce breast cancer risk. Is it safe for a woman with a history of breast cancer to eat soy foods?"

Caring4Cancer.com Response

Thank you for your thoughtful question. As with most confusing nutrition topics, there is a grain of truth to the concept that soy foods are related to estrogen. However, the concept that "Soy foods produce estrogen and therefore are unsafe for women with a history of breast cancer" is distorted and can be very misleading. We have found that this is one of the most misunderstood concepts relating to healthy nutrition for women with a history of breast or other hormone related cancer. It leads to significant and unnecessary anxiety for individuals who have been diagnosed with this disease.

Do soy foods contain or produce estrogens?

You are right in that the research studies do not support the idea that soy foods produce estrogen and therefore should be avoided by women with a history of breast cancer.

The idea that soy foods are related to human forms of estrogen comes from the fact that these foods do contain a group of nutrients that are known as phytoestrogens. Phyto means plant and estrogen means estrogen. Therefore, phytoestrogens literally can be translated as "plant estrogens". This term caught on because soy foods do contain some nutrients that look chemically similar to some of the estrogens that occur naturally in the human body (1,2).

However, it is important to note that these nutrients are not the same as naturally occurring human estrogens. Soy foods do not cause the body to produce excess estrogen and they do not contain human estrogens. However, because soy foods do contain nutrients that look a bit like human estrogens, researchers are interested in how these nutrients affect how our bodies produce and use their own forms of estrogen.

What is the relationship between soy food and breast cancer risk?

Researchers have noted that women who traditionally consume soy food as part of a normal diet, such as Japanese women living in Japan, have much lower breast cancer rates as compared to women who do not eat soy foods regularly (3-5). The results of these studies may or may not apply to women in other countries besides Japan. It is important to note that there are many differences in diet and lifestyle between Japanese and non-Japanese women. For example, Japanese women often are thinner, they may exercise more, they may have other differences in their diet, and they may have different patterns of child-bearing as compared to non-Japanese women. Furthermore, Japanese women who eat soy food may have better quality diets overall, they may eat more fruits and vegetables, and they may eat less total fat. Any of these factors may play a role in the differences in breast cancer risk between Japanese and non-Japanese women.

It would be a mistake to assume that simply adding soy food to the diet automatically will reduce risk of breast cancer.

Another important point is that many health experts feel that eating soy food during childhood and adolescence (teen years) may be more protective against breast cancer than eating these foods as an adult (6). It might be that the true protection of these foods comes from eating them earlier in life.Most research studies on this topic do not answer this question.

However, the large portion of research looking at women who eat soy foods in adulthood support that it is safe and may reduce risk of breast cancer to do so (6-11). As well, it is reassuring that at least one study tells us there is a benefit from including these foods in your diet as an adult (4).

Why did I receive conflicting information from my health care provider?

Unfortunately, the term "phytoestrogen" caught on in the popular media. Because of this many people, including health care providers, focus on this one aspect of this very complex food. In truth, soy foods appear to have many cancer fighting abilities, many of which do not have anything to do with any type of so-called "phytoestrogen" activity.

Soy foods contain dozens of different nutrients that appear to have many important functions in our bodies. They protect cells from damage, encourage damaged cells to die (rather than to keep multiplying), provide vital nutrients that control normal cell growth, and enhance cell to cell communication. In a nutshell, soy foods protect the body against many steps in the cancer process and much of this protection is not related to the 'estrogenic' activity of these foods (12,13).

However, because the popular literature focuses only on the phytoestrogen aspects of soy food, many people have the mistaken idea that soy contains estrogen. This is not true. However, in defense of health care providers, it is important to remember that it is very, very difficult to keep up on all of the research literature on this very complex topic. There are literally thousands of studies published every year just on cancer and nutrition alone. Dozens, and even hundreds, focus only on soy foods. We make it our full time job to keep up on this research and to really understand it.

In the same way that we read and study the topic of nutrition and cancer, your oncologist and other health care providers spend all of their time focused on reading the hundreds and thousands of studies that come out every year in their particular specialty areas. In other words, no one person can keep up on all of the research about cancer. There is simply too much of it. So, health care providers, just like the rest of us, are susceptible to what they read and hear in the media.

In the same way I, or any other nutritionist or dietitian cannot provide the best information on other cancer treatment areas such as surgery, radiation and chemotherapy, we believe that health care providers who do not specialize in nutrition do not provide the best information on the connection between what we eat and cancer risk. Please keep in mind that this is not to criticize your or any other health care provider. Rather we hope to give you an understanding of why people often hear conflicting information from their different health care providers.

What if I already have a history of breast or other hormone related cancer?

Now we understand that women who have eaten an "Asian style" diet that contains tofu and other soy food throughout childhood, adolescence, and adulthood have decreased risk of breast cancer. However, this still does not answer the question for women who have a history of breast or other hormone related cancer, such as endometrial or ovarian cancer.

It is important to note that what is good for cancer prevention may not be good for someone with existing cancer. This is because most cancers develop very slowly, over many years. This gives the different factors in the diet a lot of time to "intervene" and change the course of disease. Once cancer is established, cancer cells no longer behave like normal cells. This means that in the body, they don't respond to different factors such as hormones, other nutrients, vitamins and minerals.

This is confusing, what is the right answer?

The bottom line is that there is not enough research, to know with 100% certainty, that soy foods are helpful, harmful or completely neutral (neither helpful nor harmful) for women with a history of breast or other hormone related cancer.

However, at Caring4Cancer.com, after reviewing hundreds of studies on soy foods and breast cancer, we believe that soy food can be a healthy part of a woman's diet, even if she has a history of breast cancer or other hormone related cancer. 

We believe that WHOLE SOY FOODS (tofu, tempeh, miso, soy milk) can be included in the diet of women with a history of breast cancer.

However, soy foods never should be the whole focus of your best cancer fighting nutrition plan. In other words, whole soy foods are one part of a healthy, cancer fighting diet. As well, please keep in mind that women with a history of breast cancer should not consume highly processed soy foods (soy supplements, soy dogs, soy chips, soy fortified cereals, etc.). These items do not contain the same balance of healthy nutrients as whole soy food, such as tofu, tempeh, or miso. Plus, they often contain many unhealthy ingredients such as preservatives, colorings and sodium (salt).

In summary, if you are a woman with a history of breast cancer or other hormone related cancers, there is no good reason to completely avoid soy food. Neither is there any reason that you must include these foods in your diet. The choice is yours!

Practical Tips On Decision Making

Finally, before you decide if soy foods are right for you, consider these other points first. There are many, many healthy diet changes you can make to help fight cancer. These are even more important than whether you eat or avoid soy foods. Start by considering the following points.

• Are you at a healthy body weight? If not, this would be the first goal to address before adding soy foods into the diet. Solid research evidence tells us that being overweight may increase risk of breast cancer recurrence (14-16). Working toward a healthy body weight is a concrete way in which to gain control over your prognosis.
  
• Are you eating 7 to 9 servings of fruits and vegetables every day to ensure that you are following a plant-based diet? If you answered "no" to this question, start working on meeting this goal before you add soy foods to your diet. New research tells us that following the dietary guidelines of the American Institute for Cancer Research, which includes eating a wide variety of numerous servings of fruits and vegetables every day can significantly lower risk of death related to cancer and other diseases (17). For ideas on how to eat more of these foods every day, please see our information on Tips for Eating a Plant Based Diet.
  
• Are you eating the majority of your breads and cereals as whole grain foods rather than refined grains? If you answered "no" to this question, focus on meeting this goal before you are concerned about soy foods in your diet. Reviews on the ways that whole grains protect against disease tell us that these foods are an important part of a cancer fighting diet (18-20). Great whole grain recipe for you to try are Whole Grain Wheat Berry Saladand Barley Apple Salad.
  
• Do you focus on consuming plenty of variety of plant foods? For example, do you include cruciferous vegetables in your diet on a regular basis? Cruciferous vegetables include foods such as broccoli, cauliflower, and cabbage. If you answered "no" to this question, focus on meeting this goal before you are concerned about adding soy foods to your diet. Research tells us that cruciferous vegetables have terrific cancer fighting properties (21-23). These foods should be part of a cancer risk reduction diet. Great recipes to try that use these foods include Sweet Fennel Greens, Spicy Broccoli, Cauliflower, and Tofu Stir Fry, and Sweet, Spicy Kale.
  
• Many women with breast cancer are concerned about soy foods in particular. What about other legumes (starchy beans)? Do you eat these foods? Other beans are an important part of any diet to reduce cancer risk long-term (24). Beans should be part of your cancer prevention plan. Great bean recipes to try are White Bean Rosemary Soupand Lentil Sweet Potato Soup.
  
• Do you eat citrus foods, such as oranges, grapefruits, lemons and limes regularly? If not, start to include these foods in your diet. Health experts believe that citrus fruits contain numerous phytochemicals that lower the risk of cancer and other diseases (25). Try to focus on this goal before worrying about adding or avoiding soy foods. Try our fruit smoothie recipe, Sour Citrus Blast Smoothie, to add these foods into your diet.
  
• Do you consume plenty of dark red and purple berries such as blueberries, blackberries, and strawberries? These foods may help reduce risk of many types of cancer (26-28). If you are not eating these foods, start adding them in now. This is an important goal to accomplish before you focus on adding soy foods into your diet. Try our Tasty Everyday Smoothiesto get started with eating more berries.
  
• Do you eat a "high glycemic index" diet? Does your total diet have a high glycemic load? Do you eat many processed foods that contain large amounts of refined sugar? A good cancer prevention diet contains minimal processed sugars. Research tells us that eating more simple sugar and sweets in a total dietary pattern that has a high glycemic load not only may increase risk of breast cancer, but also may increase risk of dying of the disease after diagnosis (29-32). This is a very important issue to address before tackling concerns about soy foods. Eating less processed food that is high in sugar is a good step to take to eat a better cancer prevention diet.
  
• Do you consume dietary sources of probiotics? If not, this is a good goal prior to focusing your efforts on adding or avoiding soy foods. Research tells us that these healthy bacteria that are found in certain fermented foods, such as yogurt, may decrease risk of cancer and numerous other diseases (33-35).
  
• Are you getting enough exercise every week? We know that exercise helps to keep insulin levels in the body stable (36,37). This in turn may lower your risk of cancer recurrence (30). If you are not exercising regularly, talk to your doctor about starting an exercise program that is right for you. It may be as simple as walking several times each week. Check with your doctor and work together on a good exercise plan for you.

Summing It All Up

The bottom line is that the research tells us that soy food can be a healthy part of a cancer fighting diet, even for women with a history of breast or other hormone related cancer. However, do not focus only on one food when you are ready to make positive diet changes. There are many steps you can take to improve your diet before you even worry about adding or avoiding soy food.

Thank you for your thoughtful question. We hope this information is helpful to you. The concepts around soy foods and breast cancer risk often are presented in ways that are misleading and anxiety-provoking for individuals who have been diagnosed with this disease. We feel that helping people to understand the science behind the many connections between what we eat and cancer is the best way to relieve this anxiety. It is our sincere hope that this will help people make wise nutrition choices after a diagnosis of cancer!

References

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Publish Date: 10/2004