by Marion Nestle
Sep 20 2012

What to make of the scary GMO study?

I am a strong supporter of labeling GMO foods.  Consumers have the right to know.

That’s enough of a reason to support California’s Prop. 37.  There is no need to muddy the waters with difficult-to-interpret science.

My e-mail inbox was flooded with messages yesterday about the new long-term rat study reporting that both GMO corn and Roundup (glyphosate herbicide) increase mammary tumors in mice.

The study, led by Gilles-Eric Séralini, concludes:

The results of the study presented here clearly demonstrate that lower levels of complete agricultural glyphosate herbicide formulations, at concentrations well below officially set safety limits, induce severe hormone-dependent mammary, hepatic and kidney disturbances… the significant biochemical disturbances and physiological failures documented in this work confirm the pathological effects of these GMO and R treatments in both sexes.

These results are so graphically shocking (see the paper’s photographs), and so discrepant from previous studies (see recent review in the same journal), that they bring out my skeptical tendencies.  (Note: Although Séralini is apparently a well known opponent of GMOs, his study—and that of the review—were funded by government or other independent agencies.)

For one thing, the study is weirdly complicated.  To its credit, it went on for two years (much longer than the typical 90 days for these kinds of studies).

But it involves ten separate groups of 20 mice each (10 males and 10 females) fed diets containing GMO (Roundup-resistant) corn, grown with Roundup or not, or fed control diets (non-GMO corn) with or without Roundup added to their drinking water at three different levels.

I needed a Table to keep this straight.


Non-GMO Control 33% No
GMO Corn 11% No
GMO Corn 22% No
GMO Corn 33% No
GMO Corn 11% Yes
GMO Corn 22% Yes
GMO Corn 33% Yes
Non-GMO Corn 33% No 0.1 ppb (level in tap water).
Non-GMO Corn 33% No 0.09% (level contaminating feed)
Non-GMO Corn 33% No 0.5% (half the level used in agriculture)


Complicated studies require careful interpretation.  Here are the main tumor results.

LINES: The dotted line is the control.  The three corn doses (11%, 22%, 33%) correspond to thin, medium and bold lines, respectively.

BARS: 0 = Control.  R = Roundup.  A, B, and C correspond to the three levels of Roundup in drinking water.


Besides complications, the study raises several issues:

  • Incomplete data: the authors state that “All data cannot be shown in one report and the most relevant are described here.”  I’d like to know more about what the control rats ate and whether there were differences in the amounts of diets consumed, for example.
  • Lack of dose response: the authors explain that 11% did as much harm as 33% as a threshold effect.  This requires further study to verify.
  • Statistical significance: The paper doesn’t report confidence intervals for the tumor data (the bars don’t look all that different to me).

The California Prop. 37 proponents (and I’m totally with them) already have a strong “right to know” argument.  They don’t need to be distracted by the kinds of scientific arguments that are already raging about this study (see, for example, the British Science Media Centre’s collection of criticisms).

For more information about the study:

The British Sustainable Food Trust has a website devoted to this study.

Tim Carman wrote about it in the Washington Post (I’m quoted)

Andrew Pollack has a sensible piece in the New York Times

France calls for a ban on GM foods

Additional clarification: I very much favor research on this difficult question.   There are enough questions about this study to suggest the need for repeating it, or something like it, under carefully controlled conditions.

  • By emphasizing so much on how the study is “weirdly complicated”, or with “complications” you seem to be already having a biased mindset at the onset as if you didn’t want to hear about it. Your skeptical stance loses all its credibility.

  • Maje Scott

    Wouldn’t it be wise to err on side of caution regarding their findings? Until such time more 2 year trials can be performed using different variables?

  • Ewan R

    For full disclosure – I’m a Monsanto employee (so feel free to stop reading here if you’re the sort of ad hominem slinging anti-reality type I often encounter to whom this is a sticking point) and the views herein are entirely my own and not those of my employer.

    I find it weird that Seralini, having been so scathing about Hammond’s work which used 10 groups of 20 rats (per sex) being poorly designed due to too few subjects he’d then go on and lead research utilizing 10 groups of 10 rats (per sex)

    Its almost like he knew that using such a small sample size and allowing the rats to feed at will would cause some sort of effect he could torture statistical significance of a sort out of.

    You know… like he’s done in all the rest of his work around GMOs. (twisting non-biologically significant significance out of Hammond’s work, and designing his own in vitro assays which one could almost guarantee from the outset would give him the results he was after) (independant funding here is also funny – CRIIGEN is as independant in this arena as Monsanto is, one organization however discloses their conflict of interest, the other pretends there is none (just as Seralini did with his Greenpeace funded work – no conflict there, no siree Bob)

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  • I find it somewhat humorous that the same group of people who solemnly assured us that the recent study on organics is valid science, and demonstrates how unnecessary organic food is, is now the same group of people exclaiming about the flawed methodology and misuse of statistics in this study.

    My take is it would be interesting to hear a more detailed criticism of the GMO study, but I think it is valid to start conducting longer-term studies. In the US, we should be demanding such studies from the FDA, as I don’t particularly trust Monsanto studies. Unfortunately, I think we have to start becoming more wary of studies from agricultural departments of Universities, because too many of them are now dependent on Monsanto et al. Too dependent on Monsanto, and too enamored of the technology.

    As regards GMO labeling, this study has no impact, one way or another, on my views that products should have complete and comprehensive labeling.

    Thanks for links to additional information.

  • A positive note about this study: it’s not locked behind a journal paywall.

  • Mary

    Shelley: I hope you find it equally humorous that people who are demanding the organic study get retracted are flogging this one as a holy grail.

    I thought the funniest part of the study was that they were able to grow two types of corn adjacent to each other without contamination. I’m constantly told that’s not possible. Quite the wizards they are apparently.

  • Maje Scott
  • Right on Shelley! May I add that GMO products are usually officially approved after ‘only’ a 3-4 month study is carried out.

  • Jane Weiner

    I just spoke briefly to you on the phone and it was clear that you didn’t want to talk about this. As a filmmaker living in France and working on films concerning this issue, I am surprised by your response to this study (as I said when we spoke). Someone else as commented on your saying it was ‘weirdly complicated’ — of course, this is exactly what the media picked up. I’d really like to discuss this with you in more detail because the knee-jerk response of using phrases like this obviously feeds into the machine that may be mistaking your hesitation as an absolute declaration against this research. Can you please clarify to me and to all those who read your blog why you’ve reacted to this with such force..
    Many thanks in advance.

  • William Haar

    Marion, I really appreciate your informed critique of this study’s methodology. I’m voting “yes” on Prop. 37 because I believe I have a right to know what’s in my food, not because the epidemiology has convinced me that GMOs are dangerous.

    Ewan, I was excited to read your perspective but disappointed when I saw you make exactly the type of ad hominem attack against Seralini that you say others make against you.

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  • MikeB

    Marion Nestle, you are on record as stating that the FDA, the EPA, the USDA, their scientists and employees, are using us all as “guinea pigs in a great pesticide experiment.” Why should anyone take anything you have to say seriously?

  • SAO

    If anything, this shows that Round-up is bad, not genetic modification. Why not require herbicide/pesticide use be labelled?

    Why not re-examine the safety of Round-up, as used?

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  • Ewan R

    William, I don’t believe I’m making an ad hominem arguement above, I jsut find it odd that someone who is dead against studies with 10 groups of 20 rats per sex (as being too small a sample size)would then publish a study with 10 groups of 10 rats per sex – his study isn’t wrong because of this, but it is quite clear that he’s blatantly hyopcritical. Calling someone a hypocrite because they’re a hypocrite isn’t ad hominem, calling him wrong because he’s a hypocrite on the other hand is.

    My second point on him torturing the statistics also isn’t off base – he has a track record of doing this, this clearly isn’t ad hominem – he is quite obviously torturing the hell out of the stats to get anything (and omitting any reference to statistics when it appears his results probably aren’t significant (areas highlighted in Marion’s above post) ( – has a good takedown on the stats by an actual statistician (PDiff))

    My mention of the non-independance thing also isn’t the same sort of Ad hom that I am used to seeing – I don’t throw out a study because it is fudned by interested parties (I’d be rather buggered if I did right?) but do find it curious that Seralini claims no COI and has always claimed no COI when clear COI is present (non-declaration is way more fishy than an actual COI – although regardless the data should still speak for themselves (and in this case basically say nothing at all))

  • Pedro

    There’s a movie out by the Jeffrey M. Smith called genetic roulette. It discusses the GMO issue. I haven’t watched it yet but I’m guessing it’s not in favor of GMO’s. I believe it is free till the 22nd of September

  • David

    Dear Dr. Nestle,

    You have a long history as a proponent of food labeling, and the right for consumers to know about the food that they are eating. While I completely agree with the concept in principle, I have concerns about the implementation and implications of such an undertaking. My perspective is rooted in nutrition labeling, something which you have wrote about on multiple occasions (ie. FOPL). I see a strong parallel in the restriction of food labeling used to sell products by misleading consumers (ie. flavonoids in confectionary), and restriction of food labeling used to stop people from buying products by evoking fear.

    I sometimes wonder if the push to have GMOs labeled is more of an indirect tactic by people who oppose GMOs to force food processors to use non-GMO ingredients rather than risk the loss of business associated with putting a label on their product that is synonymous with “poison” in the eyes of many consumers (and now also cancer). Is the risk of GMOs different than that of pesticides?

    I suppose my question is one of consumer knowledge – is the general population knowledgeable enough to make informed choices about food? If yes, then I see no reason why products should not also be required to contain labels listing the pesticides and fertilizers used, and even the production method (ie. monoculture). At the same time, I fear that this would be used by companies to double-down on misleading nutrition labeling. Are the two concepts not the same?

    Food production is rapidly evolving, as is our knowledge of nutrition, at a rate that makes it impossible for even the experts to keep up – let alone the public. The Atkins craze of the early 2000s, and the surge in “super-foods” are just a couple examples that suggest to me that they are ill equipped to make informed choices. Rather than add to the confusion and fear around food, if there are true concerns about the safety of these products, I would submit that they should be dealt with at the level of food production.

    While it is difficult to predict the outcomes of these kinds of policies, I think it is reasonable to assume that if GMO labeling goes through, many processors will shift their production, which is certain to have some rippling effects on the future of food production and food labeling in the future.

    I certainly value your opinion on this matter, and welcome your thoughts.

  • Min

    But it’s good to know who’s funding the anti-37 campaign too.

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  • Jan Dietrick

    It is unethical to treat North Americans like unwitting lab rats, especially in light of the big rise in severe allergies, immune suppression, autism and cancer in American children. How can anyone study or report about associations when the food isn’t labeled? Where would researchers get funding for such a study even if they had any means of tracking GM food in human subjects’ diets? Take a deeper look the careful controls in this study and hold your judgement about it not being completely reported until he publishes the rest of it. It is SOP in a study to publish the results in a series of papers and to conclude that more research is needed. This is a solid study that supports longstanding health concerns about releasing these foods into the market and feeding them to our kids.
    It is phenomenal that Seralini completed a two-year peer reviewed study under the current hegemony of biotech. It is an incremental first big step we urgently need because the precautionary principle is not being justly applied after 12 years of effort through legislative means and petitions to the FDA and USDA by many concerned organizations, farmers, mothers, etc. to appropriately regulate genetically engineered food.
    You disregarded Seralini’s explanations for why the study design sets a revolutionary and comprehensive new bar for food toxicity studies of this kind. A minimum study costs $200K+. Where would such funding come from even if some other courageous researcher wanted to sacrifice his career to attempt to do what Seralini did? Yet CRIIGEN somehow put it together. FDA’s own scientists had similar hypotheses and have been forbidden to either test it or talk about the issue for over a decade. The American Academy of Environmental Medicine raised the same hypotheses urgently enough to call for a ban. Seralini is no more biased or untrustworthy than those respected physicians and our own government scientist regulators. BSF, on the other hand, is biotech, likewise ACPFG, and Pollack’s piece is as unfair and disrespectful as yours. You only reference those who are living in the biotech bubble saying that a study that does not prove safety somehow proves no harm! How could all those 200 fine studies Monsanto condones prove harm? They stop the studies when the rats start to lose weight and get sick.

  • The more I find out about the GMO corn, the more I feel betrayed by our government. I’m 18, what will food be like in another 10 years?
    I’m thankful that my parents shop at the farmers market and we eat mainly organic.

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