"Our study is now the third epidemiologic study in the recent past to report no adverse effects of soy food intake on breast cancer recurrence or total mortality--either alone or in combination with Tamoxifen.
Contrary to soy being harmful, these recent reports to varying degrees, suggest possible benefits for breast cancer survivors.
Strengths of the Women's Healthy Eating and Living (WHEL) study include being one of the few existing studies of early-stage breast cancer survivors with long-term follow-up on both recurrence and survival, as well as information on post-diagnosis soy food intake.
In summary, we found no adverse association of soy food consumption with breast cancer prognosis, even at levels similar to those consumed in Asian populations.
Our study and the two previous epidemiologic studies, taken together, which vary in racial/ethnic composition (two from the US and one from China) and by level and type of soy consumption, provide the necessary evidence that clinicians no longer need to advise against soy food consumption for women diagnosed with breast cancer."
Bette J. Caan, Loki Natarajan, Barbara A. Parker et al. "Soy Food Consumption and Breast Cancer Prognosis," Cancer Epidemiology, Biomarkers & Prevention published OnlineFirst February 25, 2011.
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So, there you have it. Good news for breast cancer survivors who have been shunning soy for years. Get yourself a copy of this study from your local medical library and ask your doctor to take a look at it.
This latest-hot-off-the-press study, published online last week, gave a thumbs-up and the go-ahead for breast cancer survivors to start eating soy. This was the third large study to analyze the effects of soy on cancer survivors.
While the earlier Shanghai & LACE studies found soy to be protective against recurrences & mortality--the U.S. WHEL study found soy's effect to be neutral or harmless.
Worth noting: The Asian women who were most benefited by soy, were eating a lot more than their U.S. counterparts were consuming The Asians were eating about 2.5 cups of soy milk or 5 ounces of tofu a day--which likely accounts for the neutral rather than protective effects that the U.S. women experienced--who were consuming about 1/2 cup of soy milk or 2 ounces of tofu a day.
Back in January, I blogged about the benefits of soy (click here for that post), and I attempted to clear up some of the misconceptions about soy and breast cancer.
Bottom Line: Worst case scenario is that it has a neutral effect on breast cancer. Best case scenario is that it helps to prevent breast cancer when it's consumed starting at a young age--and it may protect against breast cancer recurrences & mortality in adult breast cancer survivors.
The Previous Breast Cancer & Soy Research
- Recent meta-analysis on the effect of soy on breast cancer showed that it works when you consume soy as a real food, start at a young age, and eat at least 1-2 servings a day. A 16% reduction in breast cancer risk is seen for every 10 mg of isoflavones consumed in soy foods--my Eden soy milk has 69 mg of isoflavones per 1 cup. Four additional epidemiologic studies on childhood soy consumption have shown breast cancer risk reductions from 28-60%.
- Two recent landmark studies have shown that for women who already have breast cancer, those who consumed soy foods experienced a decreased risk of death or cancer recurrence, compared to those who did not consume soy. Even among postmenopausal women treated with tamoxifen, there was an approximately 60% reduction in breast cancer recurrence in the highest soy groups--compared to the lowest. Soy further enhanced the recurrence reduction rates in women who were treated with Arimidex or Tamoxifen. Click here , here, and here for the articles. All three articles noted that the women consumed typical Asian servings of soy--the highest group consumed >62.68 mg of soy isoflavones--the lowest group consumed <20 mg of soy isoflavones.
Soy Confusion - How Did Soy Get Its Undeserved Bad Reputation When It Comes to Breast Cancer?
Get this straight--phytoestrogens (plant estrogens) are very different from the estrogens our body makes. In fact, parts of phytoestrogens are anti-estrogenic.
Soy expert, Mark Messina, Ph.D, says they should be called SERMS or selective estrogen receptor modulators--the same as tamoxifen or raloxifen--the drugs used to prevent breast cancer and osteoporosis.
Here's why: OK it's kind of technical. Phytoestrogens bind to & activate beta estrogen receptors in the breast--which inhibit the effects of the alpha estrogen receptors, which stimulate breast tissue. The clinical data is very clear. You don't see the stimulation of breast tissue in women who eat soy because of the (SERM) selective estrogen receptor modultator effect of soy phytoestrogens. According to soy expert Messina, when it comes to breast tissue, it's soy food first for breast cancer protection--but in the U.S. it's unlikely we'll ever see clinical trials using soy foods--or they'll be too short or too small--and they'll likely use isoflavone supplements. If you want to study the effects of soy foods on breast cancer you have to look at the long-term Asian studies.
The New WHEL Study: The Effect of Soy Food on U.S. Breast Cancer Survivors
Who was in the study?
3088 U.S. breast cancer survivors, diagnosed between 1991 and 2000 with early stage breast cancer--followed for a median of 7.3 years. The trial ended in 2006.
What kind of soy did they eat? How much? How was it measured?
Soy intake was measured post-diagnosis--the women self-reported their soy intake via a questionnaire at regular intervals. I wish I could say that the women only consumed whole soy, but that wasn't the case. Their soy intake included tofu, "meat substitutes" like veggie burgers, soy milk, and a category called "other soy products"--maybe edamame, tempeh, soy yogurt, maybe even Tofutti (but the study doesn't get specific). Portion sizes & quantities were tracked. Follow-up on any soy supplements was also included.
Those in the lowest soy group consumed almost zero soy. The highest soy group was wide-ranging--from 16 mg to 87 mg of soy isoflavones.
Why have doctors been skittish about soy foods for their cancer patients?
Although ample studies have shown that soy food consumption protects against breast cancer, some animal & (in vitro) test tube studies have shown that isolated soy isoflavones--the major component of soy--can enhance the proliferation of breast cancer cells in the test tube, promote mammary growth in rats, and have casted some doubt that soy might interfere with Tamoxifen. Because of these doubts, physicians thought it best to advise their patients to just avoid soy.
So, what has changed? Why is it time to rethink soy for breast cancer survivors?
The two large studies--one in Shanghai (the Shanghai Breast Cancer Survival Study-SBCS) and one in the U.S. (Life After Cancer Epidemiology study-LACE)--both found that:
- Soy does not negatively affect the breast cancer prognosis
- Soy does not interfere with Tamoxifen
- Soy may actually decrease breast cancer recurrences & death in breast cancer survivors
Now comes the WHEL Study's soy component! To confirm these two studies--University of California at San Diego researchers, along with Kaiser Permanente researchers decided to use their WHEL data to see if the previous two studies' conclusions would hold up in a third study. And it did!
What subgroups were the researchers able to analyze?
The women were divided by Stage I, II, or III invasive breast cancers, race/ethnicity, age, pre & post-menopausal status, estrogen or progesterone + or -, whether or not they used Tamoxifen. Every variable was looked at. Every type of cancer or recurrence was analyzed against soy consumption.
The study's conclusions about soy?
Soy intake was not related to the risk of cancer recurrence--regardless of the cancer's hormone receptor status or the use of Tamoxifen. No significant increased or decreased risk was associated to any specific level of soy intake. Risk of death was lower as soy intake increased. And the women with the highest soy intake-->16.3 mg/day of isoflavones, which is about 1/2 a cup of soy milk or 2 ounces of tofu--had a non-significant 54% decrease in the risk of death compared to those who had the lowest soy intake. But, these risk reductions were comparable to the Chinese women who consumed similar levels of isoflavones.
Also similar to the Chinese results & the U.S. study, the largest benefits associated with soy consumption were seen in women who used Tamoxifen.
It's worth noting that in this U.S. study, even the women who ate the most soy--which was certainly a wide-ranging group, from 16.33 to 86.9 isoflavones a day--were still eating much less than the Shanghai group were eating--their highest group consumed >62.68 mg of soy isoflavones--and their lowest group consumed <20 mg of soy isoflavones.
In the Shanghai study soy food consumption was significantly associated with decreased risk of death and recurrence--and sweet spot of soy consumption was at 40 grams/day of isoflavones or 11 grams/day of soy protein--about 2.5 cups of soy milk or 5 ounces of tofu.
"The results of the Shanhai Study found that breast cancer mortality and recurrence appears to follow a linear dose-response pattern until soy food intake reached 11 grams/day of soy protein--or 40 mg/day of soy isoflavone; no additional benefits on mortality and recurrence were observed with higher intakes of soy food. This study suggests that moderate soy food intake is safe and potentially beneficial for women with breast cancer."
"We found that women in the highest soy food intake groups had the lowest mortality and recurrence rate compared with women in the lowest soy food intake group, regardless of tamoxifen use status."
Shu, XO et al. "Soy food intake and breast cancer survival" JAMA. 2009 Dec 9;302(22):2437-43.
Caveats to the study?
Because the WHEL group consists of early-stage breast cancer survivors, who were enrolled in the study 2 years after their diagnosis, the authors say that these positive results can't be generalized to women diagnosed with advanced-stage breast cancer.
Additional reading on the subject: Check out "Can Clinicians now assure their breast cancer patients that soyfoods are safe?" Women's Health 2010:6(3):335-338.
Please note: I suggest reading Eden Foods' publication--an ethical non-GMO organic best-practices company--"Sorting Out Soy Confusion" to answer any further concerns you might have about soy. And by all means choose choose whole non-GMO soy products.