A couple of years back a French research study (known as the Seralini study after it’s first author) claimed that rats fed a diet which contained a Roundup-tolerant genetically modified corn or the herbicide Roundup or a combination of the herbicide and genetically modified corn died more frequently and earlier over the two year study than control groups.
The paper was retracted last year after widespread criticism of its methodology and interpretation. The study has now been republished in a new journal.
However, despite some minor tweaks to the paper the major flaws in this study still remain. Basically, none of its claims are valid, indeed the entire study is uninterpretable.
1) the wrong controls were used - there were three concentrations of genetically modified (GMO) corn but only one concentration of non-GMO corn there should have been a non-GMO control for each concentration of GMO corn (i.e. there should have been an 11 per cent standard corn control for the 11 per cent GMO corn, a 22 per cent control for the 22 per cent GMO corn and 33 per cent standard corn for the 33 per cent GMO corn. As energy content, carbohydrate load and other components of the corn may affect tumour formation (especially when one third of your diet is now corn), this is a fundamental flaw which invalidates any conclusions.
2) there is no dose response. For a substance to be an attributable cause of cancer, being exposed to more of the substance should result in more cases of cancer this just does not happen in this study.
3) furthermore, there is no consistent response to any of the measured outcomes that would even hint at a real adverse effect.
The GMO corn had no effect on the overall number of tumours - Roundup even decreased the number of tumours in male rats, as did the combination of roundup and GMO corn in male rats (there was no consistent effect in female rats). High levels of GMO corn and high levels of roundup both reduced spontaneous mortality and pushed back the onset of death in male rats.
Yet somehow this amazing finding that Roundup protects against all cause mortality in male rats is not mentioned in the abstract or press release.
4) they didn’t use enough rats. After 2 years the strain of rats Seralini et al. used normally have between 70% to 85% of the rats developing tumours, in the absence of of any intervention. To see a statistically significant increase in tumours when most of the rats are going to develop them anyway will take a lot of animals to see any meaningful difference.
Another way to think about this is to look at the variation in tumour rates if you stuck one group of rats in a cage, and a second group of rats in another cage, then treated them identically for two years.
This experiment has been done, looking at just mammary tumours (which the Seralini paper makes a big deal of) in one group 29% of the rats had mammary tumours, and in the other identically treated group had a 50% of the rats mammary tumours. This is the sort of variation we see in the Seralini paper, the variation associated with just treating groups identically.
Conclusion
This evidence shows that all we are seeing in this recycled paper is due to random variation in a poorly controlled experiment. It does not show that GMO corn, or roundup, even at concentrations that no human would ever be exposed to through diet, have any effect on cancer or mortality.
More links
Food Standards Australia on the flaws in the original paper http://www.foodstandards.gov.au/consumer/gmfood/seralini/Pages/default.aspx
European Food Safety on the flaws in the original paper http://www.efsa.europa.eu/en/press/news/121128.htm
A major review of many long term GMO feeding trials (the ones that have been claimed not to exist) which shows no adverse effects on health http://www.foodpolitics.com/wp-content/uploads/Snell_2012.pdf
And no, I get no funding from any agricultural companies, or GMO groups or drug companies, just the NH&MRC.