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Is soy harmful during pregnancy?
Q: I’ve heard that taking soy products while pregnant can cause birth defects. Is this true?
A: Soybeans and soy products are a staple of many Asian diets, and pregnant women have consumed them without ill effects for centuries. We know of many health benefits of soy. Soybeans provide a good source of protein and are rich in many nutrients. Fermented soy products, such as tempeh or miso, contain healthy bacteria and enzymes that benefit digestion. Epidemiological studies suggest that frequent soy consumption reduces the risk of cancer, heart disease and menopausal symptoms.

Soybeans contain phytochemicals (plant-chemicals) that can act like hormones (endocrine chemicals such as estrogen or progesterone). Some of these phytochemicals weakly attach to hormone receptors in the body, stimulating or blocking the effects of hormones. Estrogen-like soy isolates have been produced to treat menopausal symptoms in women who are deficient in estrogen. During pregnancy, however, your body naturally produces high levels of hormones. It’s hard to imagine that phytochemicals from soy could have a significant impact on overall hormone levels during pregnancy.

The only research I could find possibly linking soy to human birth defects is a study that suggested that boys born to vegetarian mothers were more likely to have hypospadias, a malformation of the penis that can be surgically corrected. However, this study did not specifically measure soy consumption, and found the same association in pregnancies where the mother took iron supplements. It’s hard to draw clear conclusions from this one study.

I think that it’s fine to eat whole soybeans and soy foods during pregnancy as part of a balanced diet. It’s always best to eat a variety of foods, and I advise avoiding supplements containing high levels of soy isolates.