Soy is a staple for vegetarians looking to get their protein fix—and for meat-eaters who just can’t resist a side of edamame with their meals. But there’s been controversy over whether soy is good or bad for your cancer risk (along with whether it can contribute to other issues like man boobs, too).
Now, a new study published in the International Journal of Cancer suggests that eating foods high in certain soy compounds might actually raise your risk of aggressive prostate cancer.
In the study, researchers analyzed dietary data from over 27,000 men, and compared that to their risk of developing prostate cancer over about 12 years. They discovered that the men who ate the most total isoflavones—a compound found in plants like soybeans—were 91 percent more likely to develop advanced prostate cancer than those who ate the least.
There was no link between eating the soy compounds and prostate cancer in general or non-aggressive prostate cancer, though—only to prostate cancer that was detected at a later stage, or the kind that is more likely to spread quickly.
So what might be the link? While the study wasn’t designed to tease out what might be the cause, there are a few possibilities, says study author Jianjun Zhang, M.D., Ph.D. For one, it’s possible that isoflavones trigger responses similar to the hormone estrogen, since they are structurally similar, he says.
Estrogen has been linked to prostate cancer, because as it’s broken down, its byproducts may become “genotoxic,” says Dr. Zhang. That means they can damage genetic information in your prostate cells, possibly leading to cancer-causing mutations.
But researchers need to delve more deeply into why the link was only seen in advanced prostate cases, not prostate cancers in general. In fact, more research needs to be done on the topic in general to confirm the link, says Dr. Zhang—especially in more diverse populations where people tend to eat more soy. For example, in this study, people in the highest group of isoflavones consumed 0.75 to 2.03 milligrams (mg) a day.
For context, you’d exceed that average if you ate just one, 3-ounce serving of extra-firm tofu once a week, says Men’s Health nutrition advisor Mike Roussell, Ph.D.
So should you be worried if you supplement your diet with soy? In light of these new findings, we posed the question to Roussell.
“Totally a non-issue,” he says. “I’m not generally worried about guys over consuming soy.”
That’s because this most recent study shows an association, he stresses—not a cause and effect relationship. Plus, he says, the thinking on the estrogenic activity of soy might not be as clear as it sounds. That’s because prior data has shown that soy doesn’t actually increase levels of estrogen in men, he says. And this study didn’t look directly at how soy may or may not be influencing levels of that hormone, either.
What’s more, according to the National Cancer Institute, prostate cancer rates tend to be lower in Asian countries, where guys there tend to eat a whole lot more soy than we do here.
Bottom line: You don’t need to start switching up your dietary habits just yet based off this one study, Rousell says: “At best, this study gives researchers an association to further examine.”
Of course, if you’re still worried about soy as your protein source, there are a bunch of other non-soy options available.
By Christa Sgobba