Genetically modified foods have been around for years, but most Americans have no idea if they are eating them. The Food and Drug Administration says such foods don't need to be labeled, so some states are moving forward on their own. Vermont recently became the first state to require labeling of genetically modified organisms (GMOs). Here's a look at the debate:

WHAT THEY ARE

Genetically modified foods are plants or animals that have had genes copied from other plants or animals inserted into their DNA. It's not a new idea. Humans have been tinkering with genes (think tomatoes and turkeys) for centuries through selective breeding. What's different about genetically modified or engineered foods is that the manipulation is done in a lab. Engineers speed up the process by transferring a gene from one plant or animal to another.

IN YOUR GROCERY CART

Most of the nation's corn and soybeans are genetically engineered to resist pests and herbicides, and are used in cattle feed or made into ingredients such as corn oil, cornstarch, high fructose corn syrup or soybean oil. A papaya in Hawaii is modified to resist a virus. The FDA is considering an application to approve a genetically engineered salmon that would grow faster than traditional salmon. A small amount of sweet corn, the type we eat, is genetically modified.

what are THE potential RISKS

The vast majority of scientific research has found genetically engineered foods to be generally safe. An Italian scientist's review of 10 years of research, published in 2013, concluded that the scientific research conducted so far has not detected "any significant hazard directly connected with the use of GM crops." One French team raised safety questions. But their much-criticized 2012 study linking genetically modified corn to rat tumors was retracted in 2013 by the scientific publisher.

The main concerns for the future would be new genetically engineered foods that somehow become allergenic or toxic through the engineering process.

THE BENEFITS

There are clear benefits for the agricultural industry : for example, crops that are engineered to ward off pests or to tolerate herbicides. Also, companies such as Monsanto that produce modified seeds say their technologies will be needed to feed a rising world population as they engineer crops to adapt to certain climates and terrains. Advocates envision engineering crops to also make them more nutritious.

THE POLITICS

There is an escalating fight between labeling advocates and the food industry. In the absence of a federal labeling standard, GMO opponents have gone to the states to try to get a patchwork of labeling laws approved. That could eventually force a national standard. The National Conference of State Legislatures said there are 85 pending GMO labeling bills in 29 states. In Congress, the food industry is pushing a House bill that would head off efforts to enact mandatory labeling of genetically modified ingredients by proposing new voluntary labels nationwide — an attempted end run around the state-by-state laws.

Associated Press