June 3rd, 2011
03:51 PM ET

How much is too much phytoestrogen?

Every weekday, a CNNHealth expert doctor answers a viewer question. On Friday, it's Dr. Melina Jampolis, a physician nutrition specialist.

Asked by Keyana of Spokane, Washington:

I have two questions. What is considered to be a high/harmful amount of phytoestrogen in a woman's diet per day? And should a woman who has had cancer not take estrogen replacements or eat a diet high in phytoestrogens?

Expert answer:

Hi, Keyana. These are interesting questions. I'm going to assume that you are talking about breast cancer since the association of phytoestrogen consumption and breast cancer risk is the most concerning to many women.

Phytoestrogens are plant-based compounds that act like the hormone estrogen. There are two basic types of phytoestrogens: isoflavones and lignans.

Soy products are the most common source of isoflavones, and the controversy surrounding cancer and phytoestrogens are related to soy products. To provide you with the best possible response to your question, I turned to noted cancer nutrition expert Rachel Beller, who addresses this question on a regular basis at the Beller Nutritional Institute in Los Angeles.

Beller explained that while phytoestrogens are similar to human estrogens, their effect on human estrogen levels has not been well-researched because plant estrogens are 1,000 times weaker than the estrogen produced in our bodies.

Many studies suggest that soy isoflavones' estrogen-like effects are probably too weak to have any significant consequence on breast tissue in healthy women - that includes breast cancer survivors.

Regarding the association with breast cancer, Beller points to a 2011 study published in Cancer Epidemiology, Biomarkers & Prevention that found soy to be safe and favorable, even for breast cancer survivors, when eaten in its natural, unprocessed state - for example, tofu, tempeh, edamame, miso soup.

In fact, experts agree that fermented soy (miso, tempeh) is good for you. The fermentation process alters the chemical makeup of soy, which reduces the level of isoflavones by as much as 300%.

Therefore fermented soy foods have three times less of the chemical in question.

While this study does not conclusively establish the safety of soy, phytoestrogens aside, soy is not only an excellent source of heart healthy plant-based protein, which is encouraged in the latest dietary guidelines for Americans, it also contains dozens of nutrients that also appear to help fight cancer development.

These nutrients can protect cells from becoming damaged, encourage faulty cells to die instead of reproducing, regulate cell growth and even improve cell communication. These are all things that help strengthen your body against cancer and heart disease.

A study has also shown that consumption of soy early in life may help protect against breast cancer later in life, even if it may be more questionable for post-menopausal women.

What's also noteworthy is that Asians have been eating soy foods in large amounts for centuries, and their traditional soy-rich diets are associated with lower risks of breast and prostate cancer than Western diets.

Beller goes on to say that the "bad rap" that soy's been getting is due to the fact that when we hear something's "good for you," we process it to the max, extract the good stuff and concentrate it, which basically makes it lose its original identity.

Skip the processed soy foods and supplements, especially if you have a history of breast cancer.

The bottom line: If you have no history of breast cancer, there is no known high or harmful amount of phytoestrogens, and foods such as unprocessed soy are an important part of a healthy diet.

If you have a history of breast cancer, as with nutrition in general, you should not focus on a single food or nutrient. The key is moderation.

The phytoestrogens consumed by eating moderate amounts of relatively whole and unrefined forms of soy foods (two to three times a week) can be considered part of a healthy, complete diet.

Regarding estrogen replacement therapy, according to the National Cancer Institute, "Studies of hormone use to treat menopausal symptoms in breast cancer survivors have produced conflicting results," so I suggest speaking with your physician to determine the best approach for you.

Follow Dr. Jampolis on Twitter

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Get a behind-the-scenes look at the latest stories from CNN Chief Medical Correspondent, Dr. Sanjay Gupta, Senior Medical Correspondent Elizabeth Cohen and the CNN Medical Unit producers. They'll share news and views on health and medical trends - info that will help you take better care of yourself and the people you love.