Regularly eating soy may protect women undergoing infertility treatments from poor success rates linked with bisphenol A (BPA), according to a new study from Harvard T.H. Chan School of Public Health. It is the first study to show a possible interaction between soy and BPA in humans.

The study was published January 27, 2016 in the Journal of Clinical Endocrinology & Metabolism.

BPA is a widely used chemical found in plastic food containers, water bottles, and in can linings. More than 96% of Americans have BPA in their bodies, according to the U.S. Centers for Disease Control and Prevention. The chemical can mimic estrogen, one of the two main sex hormones found in women. Many previous studies have linked BPA with health problems, including reproductive disorders.

Researchers looked at the relationship between BPA exposure, diet, and success rates among 239 women who underwent at least one in vitro fertilization (IVF) cycle at the Massachusetts General Hospital Fertility Center from 2007 to 2012. The study found that among women who did not consume soy, higher urinary BPA levels were associated with lower chances of embryo implantation, fewer pregnancies advancing to the point where the fetus could be seen on an ultrasound, and fewer live births. However, BPA had no impact on IVF outcomes among women who routinely ate soy.

“Our study highlights the need to consider the possibility that the health effects of environmental chemicals can be modified by lifestyle factors such as diet,” said Jorge Chavarro, associate professor of nutrition and epidemiology at Harvard Chan.

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