Soy Consumption May Promote Overexpression of Breast Cancer Genes in Some Women

Soy and products made from it, like soy milk and tofu, could have an effect on genes involved in breast cancer growth.

Soy and products made from it, like soy milk and tofu, could have an effect on genes involved in breast cancer growth.

Theories abound as to which foods help or hurt in preventing cancer or easing its effects on the body. Researchers at Memorial Sloan Kettering have recently uncovered evidence that addresses one often-discussed food in many diets: soy.

In a controlled, randomized study of women with newly diagnosed, early-stage breast cancer, MSK scientists found that, in a subset of participants, adding a moderate amount of soy to the diet led to an increase in the expression of genes associated with cancer growth.

In a small portion of the women in the study, “there was evidence that genes that promote proliferation were overexpressed,” says gastroenterologist, internist, and nutritionist Moshe Shike, a coauthor of the study and leading researcher in the field of diet and nutrition.

The study was not long enough to address the question of whether these changes in gene expression would lead to enhanced tumor growth. “Although the genes were being expressed, it is not clear that this will translate into actual tumor growth,” says physician-scientist Jacqueline Bromberg, a coauthor of the study. “But the concern is that there may be the potential.”

The findings were published in the September 4 issue of the Journal of the National Cancer Institute.

A Small but Significant Effect

Study participants had recently undergone breast biopsies and were diagnosed with stage 1 or 2 breast cancer and scheduled to have a mastectomy or lumpectomy two to three weeks later. During the time between their diagnosis and surgery, the women were randomized to receive either soy protein or a placebo as part of the study.

From the original pool of participants, those in the soy group who had high levels of genistein, a component of soy, were evaluated along with patients in the control group who did not take soy to look for signs of changes in gene expression or molecular changes in their tumors.

High levels of genistein are “an indirect way of knowing whether you had actually consumed high levels of soy,” meaning those participants consumed the food, says Dr. Bromberg.

Not everyone who took the soy had high levels of genistein— and changes in gene expression were seen only in patients who did experience an increase. “Only 20 percent of those patients who took the soy had really high levels of the genistein metabolite,” she says, adding that the reasons behind that disparity aren’t clear, and that there’s no way to predict who would have this reaction after consuming soy.

Of the women with high genistein levels, a few of them experienced changes in a specified set of genes that are established to be involved in breast cancer cell growth, death, or some aspect of breast cancer pathology, Dr. Bromberg adds.

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Amount of Soy Could Be Normal for Some Diets

Though the levels of soy given to study participants was significant — about 51.6 grams, or the equivalent of about four cups of soy milk, per day — people who eat soy regularly could reasonably consume that amount throughout the course of a day, particularly vegetarians, those who don’t consume dairy, or people from Asian countries, says Dr. Bromberg.

“We’re not talking about 20 times more soy. We’re talking about something that a person could eat,” she adds.

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Best Bet Is Moderation

The study didn’t address the question of whether soy does or doesn’t prevent breast cancer, or whether soy would have any effect on women who don’t have breast cancer or have premalignant lesions.

The researchers’ general recommendation is not to avoid soy, but — like most everything else in the modern diet — to consume it in moderation. “If you currently have early-stage breast cancer, don’t eat soy in large amounts. If you’ve had breast cancer, you can eat soy, but in moderation,” says Dr. Bromberg.

“It seems reasonable to advise at this present state of the knowledge that women don’t overconsume soy,” adds Dr. Shike. “When it comes to nutrition, variety is important, and so is moderation.”

Read more about this study in HealthDay.

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As an MSK RD who works with women who have (or have had breast cancer), I'd like to highlight this sentence, because it is so important and may help assuage some fears:

"The researchers’ general recommendation is not to avoid soy, but — like most everything else in the modern diet — to consume it in moderation."

The same way it's not a great plan to eat four servings of eggs a day, it's not a good idea to eat too much of *any* given food or take unnecessary dietary supplements. There are still many benefits with a balanced, mostly plant-based diet that incorporates a wide variety of whole foods.

I would be interested to know if the scientists were just collecting data on the impacts of soy or if they had hypothesized that high amounts of soy could have negative effects and, if the latter, why? I would also be interested to know if the scientists draw a distinction between eating the actual soy bean in it's natural form or soy products that have been processed. Is there a difference in the amount or concentration of genistein?

This can be taken out of context. I have seen people post the cause and effect, already, on social media. The study says MAY not WILL. There is a difference. Too much of anything can be a problem. THere are so many gray areas. Is it the pesticides, chemicals, how it's processed, GMO, etc? This kind of thing is a license to confuse and scare the public.

I don't understand how the high-genistein group also had a few women whose growth genes were evidently activated by soy protein. But I can say this: soy protein may have enough of the key growth-promoting LEUCINE amino acid, that high consumption levels are likely to stimulate the Growth Hormone/Insulin-like Growth Factor-1 hormonal growth factor signalling pathway, resulting in growth signals in many tissues. I believe that Vegan Muscle Men actually bulk out with high doses of soy protein concentrate--and may risk dense prostate tissue, like abusers of whey protein powder [another good source of leucine]. Activation of the Insulin-like Growth Factor-1 system speeds up cell growth, proliferation, motility and metastasis [spread], while also preventing cell death [i.e. precancerous and cancer cells can survive better]. These growth signals are also strongly promoted by natural dairy growth factors and growth-activating exosomes, which accompany the leucine amino acid in milk products. We may have underestimated dairy as a major risk factor for breast cancer [and prostate cancer too]. In contrast, meat and soy protein provide only the leucine, not the additional exosomes and hormonal growth factors that make calves grow up much faster than we do.
The good news is that WHOLE soybean foods actually contain a strong anti-cancer protective compound, Inositol hexaphosphate [phytic acid; IP6], found in the skin of the bean--and also in whole grains, nuts, and [as Inositol sugar] in citrus and cantaloupe too. There are two cellular metabolites of Inositol, Inositol pyrophosphate [IP7] and Inositol pentaphosphate [IP5] that both partly BLOCK the Insulin-like Growth Factor-1 growth-activating signalling pathway. This has both anti-cancer and anti-ageing effects. Prof A M Shamsuddin, in Baltimore, has shown that IP6 can affect 100s of genes involved in cell growth, and has shown that IP6 can actually REVERSE THE EPIGENETIC PROGRAMME in breast cancer cells, causing them to "re-differentiate" into apparently NORMAL breast cells able to secrete milk protein [lactalbumin]. In other words, IP6--available from grains, nuts, legumes and citrus--can control cancer cells [cytostasis] without having to actually kill them--although very high IP6 doses can kill cancer cells. Japanese and Okinawan women who eat a traditional soy-rich diet rarely get breast cancer. Eat the whole bean.

The doctors say "a few of them experienced changes...".
Why don't they give a number or a percent instead of saying "a few".

GMO food has been proven to cause cancer....Fermented organic SOY has benefical effects...Soy has an effect on VIT B 12 ....and that is why VIT B 12 is added to soymilk....but that might not be as effective as natural VIT B 12

What about women who are positive for brca1 mutation? Does the same advice about soy apply?

Ellen, thank you for your comment. The study did not look at inherited mutations such as BRCA1 —- it included only women with early-stage breast cancer and looked at gene expression in the tumor tissue. So the study didn’t investigate any relationship between BRCA1 and soy consumption.

what is the recommendation for soy if you have breast cancer. It says to avoid large amounts, but what is the recommended amount of soy you can have.

Dear Phyllis, unfortunately, we cannot offer specific medical advice or recommendations on our blog. Please consult with your physician as to what is the appropriate amount of soy consumption for you. Thank you for reaching out to us.