How much is too much during pregnancy?
Soy has spent a lot of time in the spotlight in recent years, linked to lowering cholesterol levels and halting heart disease. The legume also packs a nutritional wallop during pregnancy. "Besides high-quality protein, soy is a great source of folate, iron, calcium, zinc and trace minerals," says Elizabeth Somer, M.A., R.D. "Soybeans are also high in fiber, and they're a source of omega-3 fatty acids."
With these nutritional benefits, soy seems like a natural choice for expectant moms. But some experts point to the negative effects of eating it in excess, leaving pregnant women wondering: Is soy safe?
Too Much of a Good Thing
Soybeans contain phytic acid, a natural plant substance that binds to minerals. "Phytic acid can block the uptake of some heavy metals like mercury, which is great, but it can also block the absorption of essential minerals like calcium magnesium, iron and zinc, which are critical for the growth and development of the fetus," says Brandon Horn, Ph.D., J.D., L.Ac., a professor of reproductive medicine at Yo-San University of Traditional Chinese Medicine in Los Angeles and an adjunct professor at the University of California, Los Angeles, David Geffen School of Medicine.
Another soy perk gone sour: Soy's ability to lower cholesterol levels is a benefit when you're not expecting. But right now your body needs cholesterol to make progesterone and estrogen, hormones that are necessary to maintain a healthy pregnancy, says Horn.
The Bottom Line
You may have heard that eating soy while expecting may lead to early puberty, irregular menstrual cycles and fertility problems in girls and an increased incidence of urological birth defects in boys. While animal studies have linked soy to such outcomes, there's no evidence that these same effects would occur in humans. But moderation is key.
"During pregnancy, one to two servings of soy daily is fine," says Somer. "A serving is half a cup of tofu or a cup of soymilk." Some experts recommend fermented soy products like tempeh and miso over more popular forms like soymilk and tofu. "Fermentation helps neutralize the phytic acid in soy, making the nutrients easier for the body to absorb," says Jonny Bowden, Ph.D., C.N.S., co-author of The 100 Healthiest Foods to Eat During Pregnancy (Fair Winds Press).
No matter which form of soy you choose, the key is to eat whole foods, not highly processed snacks. Says Bowden, "Many of the soy foods that are marketed as health foods are really just junk foods that have some soy in them, like soy nuts, soy chips and soy ice cream."
Make Room for Miso
It's easier than you think to work the fermented forms of soy (miso and tempeh) into your diet. Mix miso paste with oil for a flavorful salad dressing, or add the paste to soups. Slice and fry tempeh until the surface is crisp and golden brown; or use it in soups, salads and sandwiches. Bonus: Fermented foods contain "friendly" bacteria called probiotics, which help improve digestion and boost immunity—a nice extra coup when you're eating for two.
For more information on eating well during pregnancy, go to fitpregnancy.com/prenatalnutrition.