Soy: Breast cancer survivors can eat soy foods without risk, study finds

Breast cancer survivors needn’t worry about eating soy, according to a new study presented at the American Assn. for Cancer Research in Orlando this week.

Fears that the isoflavone chemicals found in soy -- which have estrogen-like properties -- might raise the risk of cancer recurrence seem unfounded. The conclusion comes from a large study compiling data from more than 18,000 women diagnosed with invasive breast cancer; an average of nine years after diagnosis, no statistical difference was seen between groups of women who ate a lot of soy and those who ate very little, both with regard to either recurrence of the cancers or death.

(The study, if anything, noted a trend toward lowered risk, but it wasn’t statistically significant.)

Soy has gotten mixed PR over the years. More than a decade ago when I was a freelancer, it seemed that every other article I was asked to write was about soy -- its isoflavones, its effects on hot flashes, on bone density, on breast-cancer-prevention, or how to make soy smoothies, and on which soy burgers were the most, er, tasty -- to the point where I was sick of the stuff and feared picking up the phone for fear of another soy assignment.


Then -- as is typical with miracle-food stories of this type -- early findings weren’t confirmed. It’s unclear if soy does much of anything to ameliorate hot flashes or build bone density. Its effects on breast cancer are uncertain. (It may help lower cholesterol, though.) A lot of the early surmise on the breast cancer issue was founded on large population studies that found Asian women -- who eat a lot of soy -- had lower rates of breast cancer until they flipped to a Western diet. But of course, there are many dietary and lifestyle differences that could have helped account for that.

Later on came a kind of soy backlash. For some, soy was not merely nonmiraculous: It was now a danger. Here’s an article about that we ran a few years back. (Google-search “soy” and “danger” and you’ll find plenty of examples of soy fears.)

The specter of benefit and risk have the same source -- the fact that isoflavones in soy bind to estrogen receptors. This could potentially stimulate cells to divide. (Lifetime exposure to estrogen is solidly linked to breast cancer risk.) But it could also block the receptors from being activated by estrogen. And it might do different things in different parts of the body.

Here’s what the National Institutes of Health’s National Center for Complementary and Alternative Medicine has to say about the science of soy. Among the info: “Soy’s possible role in breast cancer risk is uncertain. Until more is known about soy’s effect on estrogen levels, women who have or who are at increased risk of developing breast cancer or other hormone-sensitive conditions (such as ovarian or uterine cancer) should be particularly careful about using soy and should discuss it with their health care providers.” The new study should assuage some fears.


Soy supplements may, of course, be another matter, since these can contain levels of isoflavones you wouldn’t get from foods like tofu, soybeans or soy milk unless you consumed ridiculous quantities.