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Who Should You Believe When it Comes to the Safety of Genetically Engineered Foods?

Conflicting studies and tons of controversy surrounding GE foods are muddying up the water.

Photo Credit: Bogdan Wankowicz/


Controversy and genetic engineering go together like peanut butter and jelly, so naturally, there’s another brouhaha over genetically engineered (GE) crops in the news. Back in September 2012, a French study led by Gilles-Eric Séralini found that rats fed Monsanto’s GE corn were more likely to develop tumors than rats fed non-GE corn. The study was published in the journal Food and Chemical Toxicology, the same journal that routinely publishes Monsanto’s own studies finding that its GE corn is safe to feed to rats. Now, over two years later, the journal retracted the Séralini study.

So what’s going on? Does GE corn give rats tumors? How about people? And how do Americans, the vast majority of whom are not scientists, know what is safe to eat? Here’s a look at what the Séralini study found, why it should not have been retracted, and how to tell the difference between valid and bogus claims about GE food.

Both Monsanto and Séralini’s feeding studies follow the same general model. Get a large group of a type of rats called Sprague-Dawley and divide them into groups. Feed some groups GE corn and feed the others non-GE corn. Occasionally test their blood and urine, and watch to see if any get sick and die. At the end of the study, euthanize the remaining rats and dissect them to check their organs. Pretty simple, right?

Here are the differences. Monsanto studied its rats for only 90 days, but Séralini studied the rats for two years. Monsanto used twice as many rats — 20 male rats and 20 female rats in each group — as Séralini.

Then there’s the corn used. Both studied a variety of Roundup Ready corn called NK603. (Roundup Ready means that the corn resists Monsanto’s herbicide Roundup, so cornfields can be sprayed by Roundup, killing the weeds and leaving the corn alive.) In addition to the Roundup Ready corn that was sprayed by Roundup, as a control they used what’s known as a “near isoline.” A near isoline means corn that is genetically identical to the Roundup Ready corn, with the exception of the Roundup Ready gene. The near isoline corn was grown in the same location at the same time as the Roundup Ready corn, so they would be as similar as possible.

But each study added some additional groups. Séralini examined groups fed Roundup Ready corn that was never sprayed by Roundup. He also studied rats fed a control diet but given water spiked with Roundup herbicide. The extra groups would help find out if any impacts of the Roundup Ready corn were attributable to the Roundup and not to the corn itself.

Monsanto, for its part, added extra groups called “reference controls” that obscured its data. Rats fed reference control diets were fed various kinds of non-GE corn grown in different locations.

Whenever Monsanto found a statistically significant difference between the Roundup Ready rats and the control rats, they could often dismiss the differences by saying that the results of the Roundup Ready rats were within the normal range for the reference control rats. Michael Hansen, senior scientist at Consumers Union, compares this to a pharmaceutical company testing a drug. If the group taking the drug gains 10 pounds and the control group doesn’t, it’s not okay for the pharmaceutical company to brush that off because a 10 pound weight gain is a relatively normal occurrence within the wider human population.

Monsanto, of course, concluded that its Roundup Ready corn is perfectly safe to eat. Séralini did not, because more rats fed GE corn developed tumors than rats fed non-GE corn. What accounted for the different results?

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