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Is Soy Safe When Pregnant?

author image Janet Renee, MS, RD
Janet Renee is a clinical dietitian with a special interest in weight management, sports dietetics, medical nutrition therapy and diet trends. She earned her Master of Science in nutrition from the University of Chicago and has contributed to health and wellness magazines, including Prevention, Self, Shape and Cooking Light.
Is Soy Safe When Pregnant?
A farmer's hands holding some soy beans. Photo Credit fotokostic/iStock/Getty Images

Prenatal nutrition plays a crucial role in a healthy pregnancy, since the environment in the womb exerts a profound influence on a developing infant. Expectant mothers must take special care to get proper nutrition to facilitate fetal development and avoid or minimize exposure to substances that can have adverse effects on a fetus. Soy contains substances that have raised concerns when it comes to pregnancy, and this may lead you to wonder whether it's safe to consume soy while pregnant.

Phytoestrogen Concern

A growing fetus is extremely sensitive to hormone levels in the womb. The concern regarding soy consumption during pregnancy centers around substances found in soy called phytoestrogens. These substances may mimic the hormone estrogen. Because phytoestrogens have a structure similar to human estrogen, they can attach to estrogen receptor sites throughout your body, according to New York University Langone Medical Center. This action may either increase or reduce the effects of estrogen within the body.

May Cause Reproductive Problems

During certain periods of development, fetuses are more sensitive to estrogen exposure. Researchers conducted an animal study to examine potential risks of exposure to estrogenic-compounds from isoflavones -- phytoestrogens found in soy -- during critical pregnancy. The study found exposure to soy isoflavones altered estrogen-related reproductive activity. Researchers concluded phytoestrogen exposure during pregnancy may produce long-term reproductive consequences. The study is published in the January 2004 issue of the journal "Experimental Biology and Medicine."

Breast Cancer Risk in Offspring

Because exposure to increased estrogen in the womb may increase breast cancer risk, researchers set out to determine whether exposure to the phytoestrogen genistein -- found in soy -- alters breast cancer risk. The results of the animal experiment showed in utero exposure to genistein increased the risk for mammary tumors, and that offspring exhibited a significant increase in estrogen binding sites. The results were published in the September 2009 issue of the journal "Oncology Reports."

Things to Consider

In the "Experimental Biology and Medicine" study, researchers fed pregnant female rats levels of isoflavones similar to what a human may be exposed to through diet. Results from animal studies don't always translate to humans, however. Talk to your obstetrician about whether you should avoid soy during pregnancy if you have concerns. Data suggests growing babies are more sensitive to the estrogen levels in the womb during late gestation, so it may not be necessary to avoid soy throughout your entire pregnancy.

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