In mid-October 2006, I drove from Indianapolis to Bloomington to tour Indiana University, a prospective college. Having grown up in Connecticut, the Midwest looked like another planet to me: mile after mile of flat, verdant cropland. As I gazed at the sea of gold-tipped cornstalks, little did I know that 40 percent of Indiana corn that year was genetically modified. Six years later, that percentage more than doubled to 84 percent.

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In recent years, people worldwide have become more aware of the prevalence of genetically modified organisms, or GMOs. Nearly 2 million people participated in a global non-GMO “March Against Monsanto” in May of this year. More than 20 states, including Washington, Oregon, and Vermont, now have GMO-labeling legislation in the works. And in a game changing move, Whole Foods Market announced in March that by 2018 all items sold in its stores must include GMO labeling. “We are putting a stake in the ground on GMO labeling to support the consumers’ right to know,” said Whole Foods co-CEO Walter Robb.

But for many people, GMOs are still a mystery. What are they? How do they impact our health and environment? And what’s being done to label them? Here’s a quick overview of GMOs from seed to plate.

Made in a lab

There’s little argument over what genetic engineering is: Scientists remove a gene from one organism and transfer that gene to a different organism. Unlike traditional methods, where farmers might breed plants from the same species to make a stronger plant, GE technology makes it possible to transfer any gene from any organism into a foreign one.

For example, Bt corn, introduced in 1996, contains a gene from soil bacteria that’s toxic to insects. Scientists first isolate the desired bacterium’s DNA. “They then use a ‘gene gun’ to shoot [the bacteria] genes into a petri dish full of corn embryos,” explains Gregory Jaffe, director of biotechnology projects at the Center for Science in the Public Interest. “They hope a bit of DNA randomly gets through the corn cell membrane. If it does, scientists take that embryo and grow a plant from it.” The resulting plant expresses the gene—in Bt’s case, an insecticide—in every one of its cells, enabling the corn itself to kill bugs. This scenario would never occur in nature, but as of 2012, Bt corn takes up 67 percent of all American corn acreage.

Spread in a field

Even more widespread than Bt corn are herbicide-tolerant crops that survive spraying of glyphosate, the weed killer known as Roundup. (Fittingly, these crops are called Roundup Ready.) Companies that manufacture Roundup Ready corn, cotton, canola, and soybeans claim these crops are the solution to the world’s food problems, insisting that the GMO versions have higher yields, benefit farmers and the environment, and reduce herbicide use.

Anti-GMO activists disagree. “When [Roundup Ready] technology first came onto the market in 1996, most farmers had excellent weed control with only one herbicide application per crop,” says Chuck Benbrook, a research professor at
Washington State University who studies genetically engineered crops. “By 2000, the first Roundup-tolerant weeds started to emerge in fields and were surviving a low application rate.” Fighting these progressively more resilient weeds is a snowballing struggle because farmers must incrementally increase herbicide use. Whereas earlier farmers were forced to minimize glyphosate applications because it would kill their crops, Roundup plants are not affected by the chemicals. Since farmers adopted GMOs, they have increased herbicide use by 404 million pounds—a 7 percent jump.

This worries Benbrook. “The sheer volume of glyphosate has led to soil changes that reduce a plant’s ability to draw up various mineral micronutrients [like zinc, chromium, and manganese],” he says. This also renders plants vulnerable to bacterial and fungal attacks. The downsides? Lower crop yields, less nutrition, and more fungicide spraying.

Plus, a whole host of negative effects result from massive Roundup use. Most recently, a study published in the scientific journal Entropy suggests that long-term exposure to glyphosate residues could be linked to a suite of nasty human-health issues, including gastrointestinal disorders, Alzheimer’s, and certain cancers. As weeds continue to become even more resistant, the biotech industry’s strategic answer is to breed seed resistance to more precarious herbicides, including 2,4-D, an ingredient in Agent Orange. Frighteningly, these higher-risk chemicals have a habit of drifting to neighboring crops, which can be particularly devastating to flowering vegetable and fruit crops, says Benbrook.

Sold without labels

The Grocery Manufacturers Association estimates that a whopping 75 percent to 80 percent of conventional processed foods now contain GMOs. Even foods that don’t list corn, soy, or canola as a main ingredient can still be GMO-laden because of sneaky additives like ascorbic acid, sugar from beets or corn, lactic acid, and more.

“Products with seemingly low-risk ingredients often have ones that could contain GMOs,” says Courtney Pineau, assistant director for the Non-GMO Project, the leading non-GMO certification organization. “It’s surprising where GMOs can pop up, and it’s changing all the time.” Translation: If you’re not buying USDA Organic products—which, by definition, exclude GMO ingredients—you’re probably eating GMOs.

The jury’s still out on whether eating GMOs cause harm. Smatterings of animal studies suggest negative repercussions. For example, one study published in the Journal of Organic Systems found that pigs given GE feed had significantly more stomach inflammation than pigs eating non-GE feed. Another two-year study found that rats fed GMOs had a higher chance of developing mammary tumors.

Regardless of the GMO safety issue, non-GMO proponents insist that labeling foods containing GMOs is paramount. Nearly 60 countries, including Australia, Japan, and France, mandate GMO labeling. But the United States does not.

That lack of transparency doesn’t sit well with a lot of people. In 2012, products sporting the Non-GMO Project Verified seal fetched $2.4 billion in sales, and since Whole Foods announced its labeling initiative, the Non-GMO Project has fielded a surge of inquiries from natural manufacturers wishing to get their products certified GMO free.

The FDA maintains its position that GMOs are harmless, claiming there’s no evidence to substantiate adverse health effects. But the opposite is also true: There’s inconclusive evidence to show that they’re safe. According to a growing base of scientists, food experts, and citizens, you have the right to know what’s in your food and to choose or avoid products based on that knowledge.