There are few food-related debates more polarizing than the one around genetically modified organisms, or GMOs as they’re more commonly known. (Other than the question about whether people who like black coffee are psychopaths, that is.)

On one side of the fence, you’ve got those who claim that genetically modified foods are generally harmless. This cohort includes the American Medical Association, the World Health Organization, and 90 percent of members of the American Association for Advancement of Science.

But then there’s another sizable crew of experts, including prominent doctors (like Mark Hyman, MD, and Frank Lipman, MD), nutritionists (Ashley Koff, RD), and advocacy organizations like the Environmental Working Group, who are a bit more skeptical. Most GMO detractors claim that it’s simply too soon to tell whether there are any long-term health effects connected to this relatively young technology, which has only been around for about 20 years. And many feel there’s evidence that GMOs actually might have a detrimental impact on our health and that of the planet.

So who to believe? It’s a tricky question without a clear answer. Further complicating matters: Ordinary consumers don’t fully know how GMOs work. A new peer-reviewed study in the journal of Nature Human Behavior that interviewed 500 Americans about their stance on GMOs found that those who opposed GMOs the most understood the science behind them the least.

This years-old debate is about to resurface in the national conversation because the US government has just finalized new rules around GMO labeling, which became mandatory back in 2016 under the Obama administration. Starting in 2020, food brands will be required to disclose the presence of GMOs in their products. (More on that in a minute.)

To make sure you’re fully up to speed when the new packaging rolls out on store shelves, I tapped experts for the most up-to-date facts about GMOs—what the current science says about their health risks, how they’re impacting the environment, and whether there are any outdated myths about them that need to be dispelled. It’s never a bad thing to be too prepared in the grocery aisle, right?

First things first—what is a GMO, anyway?

When people talk about GMOs, they’re usually referring to genetically engineered crops. In extremely simplified terms, this involves extracting a gene from one organism in a lab and inserting it into the cells of another organism, bestowing the recipient cells with a new, desirable trait. In the US, there are 10 types of genetically engineered crops that are available commercially: squash, cotton, soybeans, corn, papaya, alfalfa, sugar beets, canola, potatoes, and apples. (That’s right—no wheat or tomatoes, despite what you may have heard.)

There are a few main reasons why scientists alter their crops’ DNA, says Jennifer Kuzma, PhD, professor and co-director of the Genetic Engineering & Society Center at North Carolina State University. “The first generation of genetically engineered foods took a gene from bacteria that killed insects and put it into plants,” she says. “When grown in a field, these plants kill insects on their own, so [farmers] can use fewer pesticides.”

That’s arguably a good thing, but genetic engineering can also create plants that withstand higher doses of agricultural chemicals, too. “Another reason is for weed control,” says Dr. Kuzma. “Engineers put a gene for herbicide tolerance into plants. [When] farmers spray the whole field, the plants with this herbicide tolerance gene will still grow, but the weeds will be killed.”

More recently, scientists have been using genetic engineering for other purposes, like creating an apple that doesn’t turn brown and canola oil that’s extra-rich in omega-3 fatty acids. Dr. Kuzma notes they’re also using the technology on animals—genetically engineered, rapid-growing salmon is already available in Canadian grocery stores—and they’re developing new, more efficient methods for genetically modifying foods.

Some of this new tech includes the CRISPR gene editing tool. It’s creating a lot of buzz in the food industry because it’s a faster, more cost-effective way of altering the DNA of crops. While genetic engineering makes changes in an organism that couldn’t occur in nature—like taking a gene from bacteria and transferring it to a plant—CRISPR edits the organism’s existing DNA to favor certain traits, resulting in changes that otherwise could only be achieved through the much lengthier process of traditional breeding. Scientists are currently using it to create things like low-gluten wheat and sweeter strawberries. (And since it’s so new, it’s not yet subject to government regulation—that’s not the case for the first generation of genetically engineered plants.) So expect to see more types of tech-enhanced produce on the market in the near future.

So if GMOs are in our food supply, they must be safe, right?

While you might not be eating raw corn or soybeans on the reg, you’re likely consuming more GMOs than you realize. Genetically modified crops are often used to make ingredients like corn starch and soybean oil, which are abundant in packaged, processed foods. They’re also used to feed livestock, whose meat or eggs we may eat.

Based on the latest research, this shouldn’t necessarily be cause for concern. “The majority of the studies in the scientific literature have not found any prominent adverse effects from eating genetically engineered crops or food products,” says Dr. Kuzma.

Yet there are a few reasons why GMOs still give many experts pause. As mentioned before, many GMO crops are created to withstand high levels of a weed-killing chemical called glyphosate (aka Roundup). “The International Agency for Research on Cancer deemed glyphosate as a probable human carcinogen, [meaning] any exposure to glyphosate could likely cause cancer in humans,” says Colin O’Neil, agriculture policy director at the Environmental Working Group. (Monsanto, the maker of Roundup, is facing lawsuits from hundreds of people who allege their cancer diagnosis was caused by exposure to glyphosate.)

Dr. Kuzma points out that many common grocery-store staples, like granola bars and cereals, have been found to contain significant levels of glyphosate. “That’s more of an indirect effect of eating genetically engineered crops. It’s not necessarily because of the gene you put into the crop—it’s because of the use of herbicides on the resulting crop,” she says.

Oh, and those low-pesticide crops? They might have some issues of their own. Dr. Kuzma notes that their insect-killing proteins work by piercing holes in the insects’ guts. And since humans have the same receptor for the protein as insects do, some scientists have hypothesized that our guts may also be sustaining damage by eating these foods. “The vast majority of studies have shown no harm,” she stresses. “But we are uncertain about whether or not they may be causing food sensitivities or allergenicity at a lower level when consumed over a lifetime. That is very difficult, if not virtually impossible, to test for.”

What about the environmental impacts of GMOs?

Humans aren’t the only ones you have to think about when judging the impact of GMOs. According to O’Neil, they have some pretty major implications for our entire ecosystem, particularly when we’re talking about Roundup-tolerant crops. A new generation of herbicide-resistant weeds has evolved in response to the heavy use of glyphosate, and it’s proving to be a big problem for farmers. “There have been a few cases in which farmers have just stopped farming entire fields because they’re so overrun with weeds that can no longer be killed with glyphosate, which was a mainstay in the farmer toolbox,” he says.

Sad? Yes. But the alternative is even more terrifying. “The response by the biotech industry has been to engineer crops to withstand older, more toxic herbicides like 2,4-D—one of the active ingredients in Agent Orange—and dicamba,” says O’Neil. 2-4 D is considered a possible carcinogen by the International Agency for Research on Cancer, while dicamba has proven harmful to neighboring crops and vegetation when it’s sprayed on fields. (Even so, the EPA has given farmers the green light to continue using dicamba for the next two years.)

Scary stuff. But if that’s true, why do most studies about GMOs claim they’re totally okay?

One major criticism about GMO research is that a lot of it is funded by companies that stand to benefit from positive outcomes, like Monsanto and Dow. “The industry has the resources to generate the studies—and they should use their own resources for that—and yet their studies are not very trusted by consumers,” says Dr. Kuzma.

“I caution people about this all the time—whenever you’re researching, always look at who’s sponsoring those studies because they definitely will be reporting favorable outcomes,” says Dana Hunnes, PhD, MPH, RD. Hunnes, adjunct assistant professor at the UCLA Fielding School of Public Health and a dietician at UCLA Medical Center. “You can pretty much guarantee there will be no commentary on the negative effects of GMOs, if there are any to begin with.”

And when not-so-flattering studies about GMOs actually are published, adds Dr. Kuzma, the biotech industry is often quick to try and pick them apart, as it’s in their best interest to keep developing and selling GMO seeds to farmers. “It’s kind of a sad situation on both sides—industry studies aren’t trusted, and they may be very good studies, but studies that show harm are discredited,” she says. “And I think consumers are left in a really bad position: Where do they get their information and who can they trust?” Good question.

Okay, so tell it to me straight: Are GMOs bad for you?

Unfortunately, there’s not a cut-and-dried answer right now. “The situation on safety is a little bit more complex than it’s made out to be on either side of the issue,” says Dr. Kuzma. “The scientists developing the crops and the industry will say they’re safe, and some consumer groups will say they’re not safe as a category, but neither is true. You have to look at it on a crop-by-crop basis.”

If you’d rather be safe than sorry, Dr. Hunnes says the easiest way to opt out of GMOs is to buy organic whenever possible. (Certified organic foods, by definition, can’t be genetically modified or sprayed with harmful herbicides.) And, starting in 2020, foods that have been made with genetically-modified ingredients will need to be labeled as such, thanks to the Obama-era mandate mentioned previously.

That said, not every GM ingredient will be subject to this law. For instance, ultra-refined ingredients like corn syrup aren’t included in the list, as they’re so processed that they don’t contain genetic material. Neither are meat, eggs, or seafood if the animal or fish in question ate genetically-engineered food, but it wasn’t genetically engineered itself. There’s also debate over whether the labeling will be clear, warns O’Neil. He points out that the labels will use the term “bioengineered” or “BE” in place of the much more familiar “GMO”—and that companies will have the option to use QR codes in place of full on-package disclosure. (And raise your hand if you’ve ever bothered to scan a QR code? Or even know how?)

Bottom line, according to Dr. Hunnes: GMOs probably aren’t the biggest concern we should have when it comes to nutrition, but it’s still good to be aware of what’s going on with them and decide for yourself. “Honestly, I would have to say there are other things we should worry about first,” she says, citing things like eating more fruits and vegetables. “But I do think having a concern should be valid, because we’re still dealing with parts unknown. I tend to go for organics whenever I can because I don’t personally want to be the test subject.”

This piece was originally published on December 27, 2018. It was updated on January 30, 2019. 

Turns out that washing your fruits and veggies might not be enough to reduce your pesticide exposure. So make sure to keep this year’s Dirty Dozen list in mind when you’re hitting the market.