Caution tape over burger.GMOs ahead: Proceed at your own risk.Are genetically modified foods safe to eat?

The conventional answer is “yes,” and it’s not hard to see why. Since their introduction in 1996, genetically modified (GM) or genetically engineered (GE) corn and soy seeds quickly conquered U.S. farm fields. Today, upwards of 70 percent of corn and 90 percent of soy are genetically modified, and these two crops form the basis of the conventional U.S. diet. Nor are they GM technology’s only pathway onto our plates. Nearly 80 percent of U.S. cotton is now genetically engineered, and cottonseed oil has emerged as a staple fat for the food industry. (USDA has figures on this.) Canola oil — another crop that has largely succumbed to genetic modification — is yet another common ingredient.

Given their swift path to ubiquity, wouldn’t we know by now if GMOs posed some threat? Since no obvious problems have come to the fore, some scientists — and certainly the agrichemical industry, which dominates GM seed production — have seen fit to declare them safe. Pamela Ronald, professor of plant pathology at the University of California, Davis, recently summed up the conventional view: “After 14 years of cultivation and a cumulative total of two billion acres planted, GE crops have not caused a single instance of harm to human health or the environment.”

Let’s leave aside Ronald’s claim about the environment (which is rendered suspect by the rise of herbicide-resistant “superweeds“) and dig into the human-health aspect. What we do know is that GMOs are not acutely toxic to eat. That is, we know that if you dine on a burger made from cows gorged on GM corn and soy, French fries cooked in oil from GM cottonseed, and soda laced with high-fructose syrup from GM corn, you’re not likely to keel over in agony. Tens of millions of people do it every day.

But what about more subtle, long-term effects — problems that public-health professionals call “chronic”? Here we enter less certain territory. With our highly processed diets largely deficient in fruits and vegetables, Americans have high and rising rates of chronic diseases like obesity and heart disease. Meanwhile, food allergies, autism, and non-alcohol-related liver disease have rocketed. It’s highly plausible that GMOs, which have existed in our diets for less than a generation, have emerged as another of many contributors to such long-term conditions.

So GMOs could theoretically be unsafe to eat. What does science tell us about the matter? Unfortunately, not much. Back in 1992, before the first GM seed had been commercially planted, the FDA declared GM foods to be “generally regarded as safe” — despite a complete absence of rigorous testing. And that meant that safety testing is completely unnecessary if, say, Monsanto wants to bring a novel crop to market. In a peer-reviewed 2004 paper [PDF] — which remains an extremely useful primer on regulation of GM crops —  William Freese and David Shubert show that the FDA made the “generally regarded as safe” decision over the objections of several agency scientists, who saw significant potential for harm. Moreover, when the agency rubber-stamps the introduction of a GM crop into the food supply, it does so using extremely non-committal language. As Freese and Shubert put it:

The review process outlined above makes it clear that, contrary to popular belief, the FDA has not formally approved a single GE crop as safe for human consumption. Instead, at the end of the consultation, the FDA merely issues a short note summarizing the review process and a letter that conveys the crop developer’s assurances that the GE crop is substantially equivalent to its conventional counterpart.

The authors quote from the letter the FDA sent to Monsanto on approval of Bt corn back in 1996:

Based on the safety and nutritional assessment you have conducted, it is our understanding that Monsanto has concluded that corn products derived from this new variety are not materially different in composition, safety, and other relevant parameters from corn currently on the market, and that the genetically modified corn does not raise issues that would require premarket review or approval by FDA. … as you are aware, it is Monsanto’s responsibility to ensure that foods marketed by the firm are safe, wholesome and in compliance with all applicable legal and regulatory requirements.

Shorter version: We’re approving this crop based on your word — don’t blame us if someone gets sick!

To put it more broadly, regulation of the safety of GM food is virtually nil, and research is scant and largely industry-funded. In a 2010 paper [PDF] in the journal Food Policy, researchers looked at all the papers on the health and nutritional effects of GM foods published in English between 1996 and 2009. Of the 94 studies they identified — not a large number, given the surge of GMOs into our diets over that period — 80 delivered “favorable” conclusions about the novel foods, while 10 had “negative” views and two were neutral. That sounds at first glance like a positive near-consensus around GMOs.

But then the researchers dug deeper and looked for industry ties. In 44 of the 94 total papers, one or more of the researchers had a financial or professional tie to the agrichemical industry. Of those 44, 43 had “positive” conclusions and one turned out “negative.” Meanwhile, 37 of the studies were done by independent researchers. Of those, 27 came back positive, eight came back “negative,” and two were “neutral.” In other words, near-complete consensus reigns among industry-linked scientists as to the safety of GM foods. But among independent scientists, the issue is much more contested.

In a peer-reviewed 2008 paper, Don Lotter demonstrates that only one independent long-term study has ever assessed how eating GMOs affects mammals. Funded by the Austrian government and released in 2008, that study initially seemed to reveal disturbing reproductive trouble in mice fed GMOs. But then in 2010, the Austrian government withdrew it from publication, citing insufficient data. I am trying to contact the study’s lead author, Austrian scientist Jurgen Zentek, for comment.

So where does all of this leave us? Obviously, in need of much more independent research. In April, a bit more trickled out from Quebec, Canada — and again, the results are unsettling. The study, published in the journal Reproductive Toxicology, focused on corn engineered to possess a trait from the bacteria Bt, which is toxic to a range of insects. So-called Bt corn is extremely common in the United States; according to the USDA, upwards of 60 percent of corn planted here has it. Since its introduction in the ’90s, its maker, Monsanto, has insisted that Bt corn must be safe, because the toxin embedded in it cannot survive the human digestive system.   

The Quebec study (here’s the abstract) casts serious doubt on that bedrock assumption. Researchers checked blood samples of 39 pregnant women and 30 non-pregnant women for the presence of the toxin. None were exposed directly to Bt, but all had conventional diets. The results: The Bt toxin showed up in 93 percent of pregnant women and 80 percent of their fetuses. It was also present in 69 percent of non-pregnant women in the study.   

So, 15 years after the introduction of GMOs, we know that they pose no threat of immediate, spectacular harm. That is, they won’t kill us suddenly. Whether they’re killing us slowly — contributing to long-term, chronic maladies — remains anyone’s guess.