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Should Breast Cancer Survivors Eat Soy?

10/24/2014 12:56 EDT | Updated 12/24/2014 05:59 EST

Soy? Did they say soy should be included in an anti-cancer diet?

This week the American Institute of Cancer Research (AICR) released its report on lifestyle factors that may affect survival after breast cancer. Surprise! Eating soy foods after diagnosis appears to improve your odds.

Eating high fibre foods, exercising and keeping weight under control may also help.

AICR in conjunction with the World Cancer Research Fund (WCRF) is, in the words of one researcher "the world's preeminent organization working to define evidence-based recommendations regarding how diet and nutrition impacts cancer risk and survivorship."

For the past two decades, their team of scientists from around the world have been analyzing the thousands of studies on lifestyle and cancer and producing reports periodically. Their findings have led to several recommendations for preventing all types of cancer:

 Limit alcohol, red meat, salty foods.

 Avoid processed meats.

 Eat a variety of vegetables, fruits, legumes and whole grains. .

Be lean and physically active, they also tell us.

This week's report, an analysis of 85 studies involving approximately 165,000 women, is their first to examine survival after a cancer diagnosis. While the "findings are not yet strong enough to merit making specific recommendations for breast cancer survivors," the evidence of links is "probable," they say. "(T)here is growing evidence that lifestyle choices may help to reduce the risk of having another diagnosis of breast cancer or dying from the disease," the report states.

Soy's Ups and Downs

Soy has had a controversial history. Soybeans (as well as a few other beans) contain compounds called isoflavones, including diadizen and genistein, that can act like estrogen in the body. And while these compounds, especially genistein, can also "exhibit potent anti-proliferative effect on various cancers," scientists have been concerned that they may promote hormone-sensitive cancers.

Over the past few years, several studies have been published examining thousands of women with breast cancer to see if there is an association. Their conclusion? Soy does not fuel estrogen-sensitive cancers.

In those studies, soy showed no adverse effects, did not interfere with drugs given to inhibit estrogen and in fact was associated with better outcomes. "These studies, taken together, which vary in ethnic composition (two from the United States and one from China) and by level and type of soy consumption, provide the necessary epidemiologic evidence that clinicians no longer need to advise against soy consumption for women with a diagnosis of breast cancer," researchers concluded.

How much soy may be helpful?

In those studies, the magic number for protection against breast cancer recurrence was about 25 mg/day of isoflavones, said Dr. Mark Messina, a scientist who has analyzed the data. Above that, soy seems to be safe but doesn't offer additional protection, he told me.

That translates into about a cup of soymilk a day or 1/3 cup of tofu, edamame or tempeh.

All soy, however, is not created equal, says Dr. Jeanne Wallace, who holds a PhD in nutrition and counsels clients with cancer. Soy supplements with large doses of isoflavones as well as soy protein isolates, found in many fake meats, should be avoided because they may stimulate cancer growth.

And to avoid the possibility of genetically modified soy, choose organic products.

Tempeh, a traditional Asian food, has another advantage: It's fermented, meaning bacteria are added to whole soybeans.That's good for two reasons: Fermentation makes soy's proteins and minerals easier for your body to absorb. And the bacteria, when they arrive in your gut, help produce important fatty acids that control inflammation, regulate appetite and blood sugar and fight cancer.

The fibre connection

And that's where fibre comes rolling in -- specifically fermentable fibre from various plant foods.

Many nutrients in plants get digested in the small intestine and pass directly into the bloodstream. Their leftover fibre then continues to the large intestine, which houses colonies of bacteria, both good and bad. There, the health-promoting bacteria combine with fermentable fibre to produce those key fatty acids. Some types of plant fibre -- legumes and alliums, for example -- actually provide the good bacteria as well.

Even if fibre is not fermentable, it still serves a purpose. Fibre traps toxins, including excess estrogens, and then moves them out of your system, assuming everything's working well. If your transit time is slow, however, or your intestinal lining compromised (a common side effect of chemotherapy), toxins can seep through the lining back into your blood. Butyrate, one of the fatty acids produced by bacterial fermentation, helps heal the lining,

Beyond soy and fibre

This week's AICR report offered more dietary guidance for breast cancer survivors: Keep weight under control. That's not a surprising finding. Overweight women and men are at greater risk for many types of cancers, for several possible reasons.

Fat tissue, especially around the abdomen, is biologically active. "(I)t produces proteins that cause inflammation, which can promote cancerous changes in cells and tissues, " says AICR. Being overweight also" increases blood levels of insulin, estrogen and other hormones that can encourage the growth of cancerous cells."

"Physical activity may influence breast cancer outcomes through its effects on hormones and by helping women prevent weight gain," AICR says.

Are you ready to calculate your Body Mass Index before heading out for a brisk walk? Have a look at this handy chart. Meanwhile, now that we've got permission, I'm heading into the kitchen to perfect my recipe for Tempeh Wraps with Red Curry Sauce -- soy and fibrous collards and button mushrooms, which also seem to inhibit estrogen.

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