So Much On Soy!

A couple of weeks ago the headlines were bold "Soy no safe for breast cancer survivors to eat""Soy may actually prolong breast cancer survivors life" "Soy actually decreases the recurrence rate". I got really excited and were reading on the headlines and the articles.

If soy was somehow protective, I would go back to my edamame, soy milk and tofu (all occasionally) ways. Anything to support nutritional science.

What generated these wonderful headlines? That would be the Study by Zhang et al titled Dieatray Isoflavone Intake and All Cause Mortality in Breast Cancer Survivors: The Breast Cancer Family Registry (DOI: 10.1002/cncr.30615). This study used 13,000 families from the United States, Canada, and Australia. However, because a different Food Frequency Questionnaire (FFQ) was used for Australia, the Australian population was not included in their end analysis. After exclusions, the study involved 6,883 women. Each woman was given an FFQ and each woman self reported their cancer treatment history and ER/PR status of their cancer was obtained for record. The study also used self reported weights and heights (this cracked me up, because I wondered how many people shaved a couple of pounds off, or reported how tall they used to be).

The study looked at isoflavone intake; isoflavones come from whole food soy (soy milk, edamame and tofu). And the study showed that there was a 21% lower all cause mortality associated with high isoflavone intake after following the group of woman for longer than 9 years. Those are good numbers!

However, the biggest key piece is that the reduction in mortality was only for those women who had ER/PR negative tumors and those who were not receiving hormone therapy. ER?PR positive tumors are the most common form of breast cancer and this means that these great headlines about extending survival and decreased risk of recurrence does not apply to most women and none who are receiving hormone therapy.

So I will continue to avoid soy protein isolate and I will likely consider continuing to not eat edamame, tofu and soy milk.

Another study on soy consumption over the lifetime and response to tumors came out in February. Researchers fed rats a high soy diet over a lifetime (to simulate a typical Asian diet intake) and then fed other rats higher soy intake as adults (to simulate a typical Western diet) and the rats were given ER+ tumors. Now, this study was in animal models, which doesn't always translate into humans. The researchers found that high lifetime soy intake was protective against the development of mammary tumors and that those who where lifetime consumers of soy while on tamoxifen had better response to the therapy. However, they researches found that the rats that started consuming soy during tamoxifen therapy or as adults the tumors didn't respond as well to the tamoxifen therapy. The rats that started eating soy as adults and not over a lifetime had a significantly higher tumor burden. (Zhang X et al, "Lifetime Genistein Intake Increases the Response of Mammary Tumors to Tamoxifen in Rats" doi: 10.1148/1078-0432.CCR-16-1735).  Yes, its only an animal model but it s demonstrating that maybe you shouldn't start eating soy later in life for a protective affect.

Bottom line, I am going to continue to not eat soy and work on my overall fruit and vegetable intake.