Should you avoid eating soy-based foods?
Do they increase your risk for cancer?
How much is safe?

These are all questions I’ve gotten over the course of my nutrition classes that I run for cancer patients. It is also something I’ve wondered about for myself. As a vegetarian, I often look to soy as an alternative source of protein.

The Cause for Concern:
The natural active compounds in soybeans are called isoflavones. These compounds mimic the hormone estrogen. It’s thought that the body’s own estrogen can promote the growth of breast-cancer cells. After reading through quite a bit of literature on isoflavones for my Master’s research project,  I found that although they bind to the estrogen receptor and mimic the action of estrogen, they exhibit a much weaker effect than endogenous estrogens and may actually block the effects of estrogens in some tissues.

Observational Studies:
There has been an observed lower breast cancer incidence in Asian countries (where soy intake is high) relative to Western countries (where soy intake is low).  However it is important to remember that many factors can contribute to this observed geographical difference in breast cancer, such as environment.

soy and cancer

Key Points From the Literature
The following points are summarized from four meta-analysis studies (Qin et al., 2006, Trock et al., 2006, Wu et al., 2008, Don et al., 2011).

  • Consumption of soy isoflavones has been studied in relation to breast cancer prevention with the majority of studies showing either a protective or no significant association.
  • Breast safety studies of soy isoflavones do not reveal cause for cancer when examining functional endpoints such as mammographic density and breast cell proliferation.
  • Studies of women who are breast cancer survivors have so far been observational in design and do no report adverse relationship between soy expose and breast cancer recurrence or mortality. In fact, some of these studies report reduced risks of breast cancer recurrence or mortality.

How Much Soy?

  • The results of the above studies support the idea that moderate soy food consumption is not of concern. Moderate consumption refers to no more than 3 servings of soy foods a day.
  • It is important to note that this refers to soy foods and not supplements. Soy isoflavones in the form of supplements or concentrated powders should be avoided by breast cancer survivors.

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