Soybeans, corn, cotton and canola -- most of the acres planted in these crops in the United States are genetically altered. "Transgenic" seeds reduce the use of some insecticides. But herbicide use is higher, and respected experts argue that some genetically engineered crops may also pose serious health and environmental risks. The benefits of genetically engineered crops may be overstated.

We don't have the complete picture. That's no accident. Multibillion-dollar agricultural corporations, including Monsanto and Syngenta, have restricted independent research on their genetically engineered crops. They have often refused to provide independent scientists with seeds, or they've set restrictive conditions that severely limit research options.