What you need to know about GMOs

What is it? Genetically modified foods are plants or animals that have had genes copied from other plants or animals inserted into their DNA. While farmers have been selectively breeding plants for centuries, this manipulation is done in a lab, speeding up the process by transferring a gene from one plant or animal to another. The engineering is done to create certain traits, like resistance to herbicides.

The bulk of the nation's genetically engineered crops are corn and soybeans that are eaten by livestock or made into popular processed food ingredients like cornstarch, soybean oil or high fructose corn syrup. Only a handful of genetically engineered fruits and vegetables are available in the produce aisle — Hawaiian papaya, some zucchini and squash and a small percentage of the sweet corn we eat, for example. The food industry says about 75 percent to 80 percent of foods contain genetically modified ingredients — most of those corn and soy-based. The Food and Drug Administration says they are safe to eat.

What happens next? The Agriculture Department has two years to write the rules. The legislation allows USDA to determine how much of a "bioengineered substance" must be present to determine the food should be labeled GMO. Labeling advocates say many foods wouldn't be labeled if the department sets a high threshold. Once President Obama signs the bill — which the White House said he will do — the law will pre-empt a Vermont law that kicked in earlier this month.

Why should there be labels? While there is little scientific concern about the safety of those GMOs on the market, advocates for labeling argue that not enough is known about their risks and people want to know what's in their food.

Associated Press