Genetically Modified Foods and Safety

Honest opponents of genetically modified1 foods do not actually claim that GM foods are unsafe. Instead they write about the lack of long-term safety studies or a lack of evidence for safety. Less scrupulous opponents will claim that very scary results have been seen from GE foods. This post is about a few of them and why they aren’t nearly so scary as they seem or in some cases are likely not even there.

Note: This post is part of a short series on issues around GMO labeling. See the intro post for more information.

Scary Claim #1: GM potatoes were toxic in rats!

This is almost always a reference to the work of Árpád Pusztai who did some work on rats and a GM potato variety. The Lancet published his work but it was immediately criticized for major flaws including feeding the test animals inappropriately (the experiment and control potatoes differed in protein content). The Royal Society reviewed the work and found it unconvincing. As far as I know the work has not been replicated. You can read more about it at biofortified. The point here is not to claim there are no problems with this GM potato, but that a single heavily criticized study is insufficient to make a health claim about a single GM food, much less all of them as is often the case.

Scary Claim #2: GM toxins were found in the blood of pregnant women!

I’ve previously discussed the origin to this claim in my post about Senator Sanders’ bad GM label amendment. I don’t want to rehash the content of that post but, in summary, the researchers used a likely invalid method to detect Bt toxins (“Cry” proteins) in blood. Beyond the problems with the study itself is that it is used to claim some negative affect on people when the study (at best) just showed a very tiny level of the protein in blood. Moreover, the researchers did not attempt to trace the origin of the toxin (was it GM corn? or Bt residue from external application). Bt toxins have not been found in the blood of other mammals even though researchers have tried in both pigs and cows. The important point remains that this scary claim implies that some harm comes from the presence of the toxin when this is not the case. We haven’t seen harm despite over 50 years of Bt toxin use: more than a single study is needed to show a problem with Bt trait crops.

Scary Claim #3: GM corn causes kidney (or organ) failure

This claim usually refers to the work of Séralini, usually this paper. The problem here is that the authors used data from Monsanto itself, re-analyzed it and claimed statistical effects. But no one has found any any mechanism for the claimed effects (which weren’t even organ failure despite the scare story). His work has been repeatedly criticized, including by the European Food Safety Authority. One major problem with this study includes statistical effects at lower doses not seen at higher doses (see Table 2 in the original paper, for example) with no explanation of why this might be the case. Moreover, there are numerous other studies showing no similar effects. To claim that GM corn causes organ failure on the basis of one lab’s unreplicated work is not sound.

But are they safe?

This post isn’t meant to be exhaustive proof that GM foods are safe. Indeed, no such proof is possible — absolute safety just isn’t something that science can prove. All we can do is say the preponderance of evidence suggests one thing or another. In the case of current genetically modified foods, it appears they are safe to eat. When you read a scary story about safety of GM foods, consider looking for contrary evidence: it might not be as scary as it seems. Strong claims require strong evidence.


As before, “genetically modified”, GM, GMO, GE, etc. are primarily used to refer to transgenic organisms. See Kevin Folta’s post on the difference kinds of modification.