Scientists are still debating whether it's wise to avoid eating foods that contain genetically modified organisms, or GMOs—and with good reason. Just a decade ago, these were not part of our food supply. Today 30 percent of U.S. cropland is planted with genetically modified seeds. "It's a huge change in a very short time," says pediatrician Alan Greene, MD, author of Raising Baby Green (Wiley, 2007).

Most Americans don't believe foods made with GMOs are entirely safe. But according to a 2003 study by the Pew Initiative on Food and Biotechnology, more than 60 percent also don't believe they've ever eaten any. In fact, most Americans eat them every day, mostly in processed foods, in the form of ingredients derived from corn, soy, cottonseed, and canola. (Certified-organic producers agree not to use genetically modified seeds or ingredients.)

To genetically modify a plant, scientists splice (or shoot) in a desired foreign gene—from a fish, a petunia, even a human—that's intended to help the new organism resist pesticides, pests, or freezing. At the same time, they also insert a virus or bacteria, which helps the foreign gene invade the host cell, and an antibiotic marker gene, which helps to determine whether the splicing worked.

The long-term effects of these new organisms, both on our planet and our bodies, are unknown. Scientists do know that brand-new proteins have been introduced into our food supply, raising concerns about new allergies—our immune systems' overreaction to proteins. Food allergies indeed have been on the rise. In fact, childhood allergies to peanuts (closely related to soy) doubled between 1997 and 2002, according to research published in the Journal of Allergy and Clinical Immunology (2003, vol. 112, no. 6). "Whether genetically modified foods caused it or not, we don't know, "Greene says. "But that's kind of the point. I'd rather people—especially small kids and pregnant women—at least have the choice to use foods we've been eating for millennia."

In the European Union and Japan, where foods with GMOs are labeled, consumer pres-sure essentially has driven these products off the shelves. Because the USDA chooses not to label genetically modified foods, U.S. consumers can avoid them only by choosing organic.

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