GMO corn causes cancer–Myth vs. Science (recent news)


Genetically modified crops are foods derived from genetically modified organisms (GMOs), and all types of agricultural breeding induces genetic modification, but in general, GMO usually implies actual manipulation of the genes. The major controversy surrounds the use of DNA recombination-introducing genes from one species into another. Despite all of this controversy, there is an amazing lack of data that shows that GMO foods are unsafe. In fact, there are secondary reviews that show it is safe


This week, the interwebs exploded because of an article (pdf) published in Food and Chemical Toxicology by Gilles-Eric Séralini et al. that show health problems in rats fed genetically modified corn which is resistant to the herbicide Roundup. They also found similar health problems in rats fed the herbicide alone (along with non-GM feed). The rodents experienced hormone imbalances, along with more and larger mammary tumors, earlier in life, than rats fed a non-GM diet. The authors claimed that the GM- or pesticide-fed rats also died earlier.

Séralini et al. states this is the first time it has been tested for toxicity throughout a rat’s lifespan even though this type of GM corn accounts for more than half of the US crop.

Well, this peer-reviewed article went viral on the internet, being reported at the center of the pseudoscience universe, Natural News:

Eating genetically modified corn (GM corn) and consuming trace levels of Monsanto’s Roundup chemical fertilizer caused rats to develop horrifying tumors, widespread organ damage, and premature death. That’s the conclusion of a shocking new study that looked at the long-term effects of consuming Monsanto’s genetically modified corn.

They conclude the story in big bold 30 point type: 

Spread the word: GMOs are toxic!

Oh no. And yes, this meme is flooding Facebook and Twitter. But now we go to my favorite part…


Before we start with the scientific takedown of Séralini et al., let’s remember something I’ve written before–it is best to avoid primary sources (ones in which the authors directly participated in the research or documented their personal experiences). It is much better to utilize secondary sources–which summarizes one or more primary or secondary sources, usually to provide an overview of the current understanding of a medical topic, to make recommendations, or to combine the results of several studies. The reason secondary sources are so valuable is that they combine the works of several authors (and presumably locations), eliminating biases of one laboratory or one study. Séralini et al. is a primary study, and we cannot determine its value compared to the vast body of work in GMO research which do not share its findings.

Another issue that I find with Séralini is that his group has a long history of opposing GMO crops, not even attempting to show an unbiased approach to research. Poisoning the well is a well-worn logical fallacy of those who want to dispute the quality of research in medical products (Big Pharma funds that!), so this is a form of it, but researchers should at least try to be unbiased.

New Scientist provided an excellent skeptical analysis of the research, which identifies a list of significant problems with the study:

  • The rats used in the study seem to have a genetic predisposition for tumors. According to Tom Sanders, head of nutritional research at King’s College London, the strain of rat is predisposed to breast tumors, especially when given unlimited food; when corn is contaminated by a common fungus that causes a hormone imbalance; or when they are just allowed to age.
  • There were a lot of statistical anomalies to the data. For example, there were only 20 rats in the control group, while 80 in the exposure group. This is both a small total population, and very asymmetrical. In addition, the paper reports that only “some” of the test groups had a higher tumor incidence, so it appears that there was some cherry picking of data. It’s frustrating when a peer reviewed paper sounds like the authors intentionally discarded data that did not support their conclusion. 
  • In fact, some of the test group, those that ate the GM foods were healthier than the controls. Yes, read that again. Some of the rats fed the GM corn foods were healthier. Why wasn’t that broadcast by Natural News?
  • There were other statistical issues. New Scientist pointed out that “Toxicologists do a standard mathematical test, called the standard deviation, on such data to see whether the difference is what you might expect from random variation, or can be considered significant. The French team did not present these tests in their paper. They used a complicated and unconventional analysis that Sanders calls ‘a statistical fishing trip’.” Missing something as basic as a standard deviation? I don’t think you could write a paper in a high school science class without showing the significance of results without including a standard deviation.
  • Oddly, Séralini et al. claims that exposure to GM corn or the Roundup herbicide has the same effects to the rats. Now, this might not be impossible, but it is highly unlikely that a chemical like Roundup would have an identical toxic effect as a plant with a gene that destroys Roundup. It would take a huge leap of biological inventiveness to find some pathway that explains both Roundup and GM corn having the same exact effect. That would violate Occam’s razor, when answering a problem in science, one should never make more assumptions or posit more causes than the minimum necessary.
  • There was no dose response study, a minimum requirement for toxicological relationships. Without it, it’s impossible to determine whether the stressor (either the pesticide or the corn) has some level where it causes an effect, because the expectation is that as the dose increases, so should the effect.
  • The researchers did not control for the food amounts, especially considering that the rat strains were sensitive to tumors when they overeat. This was a ridiculous oversight on their part.
  • “They show that old rats get tumours and die,” says Mark Tester of the University of Adelaide, Australia. “That is all that can be concluded.” That’s a bit different than what’s flying around the internet.

What the Skeptical Raptor says

Right now, there is just little evidence that GM crops are dangerous. It’s the fear of science, rather than science providing us evidence of something of which to be afraid. This study was terrible with bad design, bad statistics, bad results, and bad conclusion.

I wouldn’t eat crops with Roundup on it, because I prefer to not eat herbicides. As for GM food, I’m just not worried. Why? Because there is no evidence. And because there just isn’t a plausible and realistic mechanism that a genetically modified food can harm a human, unless there’s some amazing new physiological process that’s unknown to all the brilliant physicians and researchers in the world.

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The Original Skeptical Raptor
Chief Executive Officer at SkepticalRaptor
Lifetime lover of science, especially biomedical research. Spent years in academics, business development, research, and traveling the world shilling for Big Pharma. I love sports, mostly college basketball and football, hockey, and baseball. I enjoy great food and intelligent conversation. And a delicious morning coffee!