Cancer and Soy Products

Have Americans have been misled about the health benefits of soy products and the relationship between soy and cancer?  Based on various polls, most Americans are under the impression that soy products like soy beans (edamame), tofu and miso, are unhealthy and promote or even cause cancer, particularly breast cancer.

Much of the misconceptions and confusion about soy stemmed from widely publicized laboratory animal (rodent) studies, some of which showed possible harmful effects.  However, human studies have shown different results.  According to Eat to Defeat Cancer, a global campaign that aims to crush the cancer epidemic by getting people to eat foods that starve cancer "... theoretical concerns that soy intake may worsen breast cancer or interact with tamoxifen treatment has now been thoroughly dispelled by the results of multiple studies."  

The following are but a few articles that summarize and/or help to explain the results of various studies concerning the consumption of soy products and cancer risk:


Foods that Fight Cancer:  Soy - AICR's Foods That Fight Cancer™
According to the American Institute for Cancer Research (AICR):  Soy foods contain several key nutrients and phytochemicals studied for their cancer prevention properties. Many soy foods also contain dietary fiber, which links to lower risk of colorectal cancer. Soy foods contain isoflavones, which are phytoestrogens that in some ways mimic the action of estrogen. Because high levels of estrogen link to increased breast cancer risk, there was a fear that soy foods – and its isoflavones – may increase risk. Yet overall, human studies show soy foods do not increase risk and in some cases, research suggests they may lower it.

Soy is Safe for Breast Cancer Survivors (New Review of the Research) - The American Institute for Cancer Research
According to the AICR:  Scientists now know that rodents and most other laboratory animals metabolize soy isoflavones differently than humans and that soy consumption does not lead to increased estrogen levels in humans.  Six recent human studies and one major meta-analsys have found that consuming moderate amounts of soy foods does not increase a breast cancer survivor's risk of recurrence or death.

Soy and Breast Cancer:  An Update - Michael Greger, MD, Nutrionfacts.org
According to Dr. Greger:  We’ve known that regular soy consumption appears to both prevent breast cancer and prolong survival in women battling the dreaded disease, but we haven’t understood why.  A new study measured estrogen levels inside the breasts themselves of women placed on a high versus low soy diet. This was accomplished by aspirating ductal fluid from the nipple, which is what bathes the very cells most likely to turn cancerous. After 6 months, the researchers found a trend towards lower estrogen levels inside the breasts of women eating two servings of soy foods a day. Not only does this aid our understanding of why soy may shield us from cancer, but can help explain the findings presented in The Effect of Soy on Precocious Puberty (Video), which documents new research suggesting young girls drinking soymilk just twice a week may be protected against premature puberty.

Soy Consumption Associated with a Decreased Risk of Breast Cancer Recurrence by Roderick Smith, M.S., Eat to Defeat Cancer™
Since soy isoflavones are similar to estrogen, there have been concerns that soy can potentially promote breast cancer recurrence and possibly blunt the effects of the estrogen blocking drug tamoxifen. A major study conducted in more than 5,000 Chinese breast cancer survivors found that high soy consumption was in fact associated with a reduced risk of breast cancer recurrence and overall mortality regardless of whether they took tamoxifen or whether their breast cancer was estrogen receptor-positive or negative. These findings should help reassure women who have had breast cancer that soy intake is safe and even beneficial. - See more at: http://www.eattodefeat.org/evidence/374/soy-consumption-associated-with-a-decreased-risk-of-breast-cancer-recurrence.html#sthash.ThWaFuCx.dpuf
Since soy isoflavones are similar to estrogen, there have been concerns that soy can potentially promote breast cancer recurrence and possibly blunt the effects of the estrogen blocking drug tamoxifen. A major study conducted in more than 5,000 Chinese breast cancer survivors found that high soy consumption was in fact associated with a reduced risk of breast cancer recurrence and overall mortality regardless of whether they took tamoxifen or whether their breast cancer was estrogen receptor-positive or negative. These findings should help reassure women who have had breast cancer that soy intake is safe and even beneficial. - See more at: http://www.eattodefeat.org/evidence/374/soy-consumption-associated-with-a-decreased-risk-of-breast-cancer-recurrence.html#sthash.ThWaFuCx.dpuf
A major epidemiological study of more than 5,000 Chinese female breast cancer survivors, in which researchers collected detailed data from the women about their diets, lifestyle and post-cancer treatment at 6, 18, 36 and 60 months after their diagnosis, found that a high soy consumption was, in fact, associated with a reduced risk of breast cancer recurrence and overall mortality, regardless of whether or not they took tamoxifen or whether or not their breast cancer was estrogen receptor positive or negative.

Soy Products Improve Survival in Women with Lung Cancer - The Physician's Committee for Responsible Medicine (March 27, 2013).
A new study published in the Journal of Clinical Oncology, in which researchers examined the diets of 444 women who were diagnosed with lung cancer, found that those women who ate the most soy products cut their risk of dying by nearly half, compared with those who ate the least amount of soy.  According to PCRM, previous studies have shown that soy products reduce the risk of developing lung cancer, and have a similar ability to reduce the risk of breast and prostate cancer.

Image:  WikiMedia Commons


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