Soy and Breast Cancer: 5 Myths and Facts
2. Myth: All types of soy have the same effect on the body.
Your body may process the natural soy in tofu, miso, and soy milk differently than the kind that’s added to processed foods.
The soy protein isolate found in supplements, protein powders, and meat substitutes is usually stripped of nutrients, such as fiber.
“It’s also a more concentrated form of soy,” Millstine says. “So you’re much more likely to get a high dose if you’re having protein shakes and soy hot dogs than if you’re eating edamame.”
Researchers aren’t certain how large amounts of soy affect breast cancer risk. In one early study, soy supplements were shown to “switch on” genes that encourage cancer growth in women with early-stage breast cancer.
Experts recommend sticking with a moderate amount, or about one to two servings, of whole soy a day. One serving includes:
- Half a cup of cooked edamame
- 1 cup of soy milk
- 1 ounce of soy nuts
- 3 ounces of tofu
3. Myth: Eat soy to protect against breast cancer.
While eating a moderate amount of soy is fine, it’s too soon to suggest eating more to protect your breasts.
“The results are promising, but there’s still not enough information,” Meyers says. Experts now believe that soy isoflavones may actually block estrogen from attaching to breast cancer cells instead of spurring growth like once thought.
Meyers notes that many of the hallmark studies are done in Asian countries, where people grow up eating soy in its traditional forms. “That may influence the way their body processes soy,” she says. “We need to look at if having soy later in life has the same effect.”
More research also needs to be done on how much soy you get at different ages. “Soy may have more of an impact on a postmenopausal woman who’s not producing as much estrogen as a healthy 20-year-old,” Millstine says.
4. Myth: If you have or had breast cancer, avoid all soy foods.
Just as eating a moderate amount of whole soy doesn’t make you more likely to get breast cancer, it also doesn’t seem to raise your risk for recurrence.