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New Scientist Health reports:

It's back. A controversial study purporting to show that genetically modified food causes health problems was republished this week in the journal Environmental Sciences Europe (DOI: 10.1186/s12302-014-0014-5). It was retracted last year by Food and Chemical Toxicology, which published it in 2012.

The research by Gilles-Eric SÚralini of the University of Caen in France, claims that rats fed the modified maize suffered kidney, liver and pituitary problems. But the original was slated by toxicologists for its poor use of statistics, and the republished study has received just as much criticism.

Here's what New Scientist's Debora MacKenzie wrote back in 2012 when the study was first published.

Original article, posted 19 September 2012

Today, researchers led by Gilles-Eric SÚralini at the University of Caen in France announced evidence for a raft of health problems in rats fed maize that has been modified to be resistant to the herbicide Roundup. They also found similar health problems in rats fed the herbicide itself.

The rodents experienced hormone imbalances and more and bigger breast tumours, earlier in life, than rats fed a non-GM diet, the researchers claim. The GM- or pesticide-fed rats also died earlier.

This kind of GM maize accounts for more than half the US crop, yet the French team says this is the first time it has been tested for toxicity throughout a rat's lifespan (Food and Chemical Toxicology, DOI: 10.1016/j.fct.2012.08.005).

Are the findings reliable?
There is little to suggest they are. Tom Sanders, head of nutritional research at King's College London, says that the strain of rat the French team used gets breast tumours easily, especially when given unlimited food, or maize contaminated by a common fungus that causes hormone imbalance, or just allowed to age. There were no data on food intake or tests for fungus in the maize, so we don't know whether this was a factor.

But didn't the treated rats get sicker than the untreated rats?
Some did, but that's not the full story. It wasn't that rats fed GM maize or herbicide got tumours, and the control rats did not. Five of the 20 control rats - 25 per cent - got tumours and died, while 60 per cent in "some test groups" that ate GM maize died. Some other test groups, however, were healthier than the controls.

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".

Anthony Trewavas of the University of Edinburgh, UK, adds that in any case, there should be at least as many controls as test rats - there were only 20 of the former and 80 of the latter - to show how variably tumours appear. Without those additional controls, "these results are of no value", he says.

Aside from the statistics, are there any other problems?
Yes. Tests like this have been done before, more rigorously, and found no effect of GM food on health. The French team claims to be the first to test for the animal's whole lifespan. But "most toxicology studies are terminated at normal lifespan - 2 years", as this one was, says Sanders. "Immortality is not an alternative." And those tests did not find this effect.

Furthermore, the team claims to see the same toxic effects both with actual Roundup, and with the GM maize - whether or not the maize contained any actual herbicide. It is hard to imagine any way in which a herbicide could have identical toxic effects to a gene tweak that gives the maize a gene for an enzyme that actually destroys the herbicide.

Does seeming unlikely mean that this is an invalid result?
Not necessarily. But even more damning from a pharmacological perspective, the team found the same effect at all doses of either herbicide or GM maize. That's unusual, because nearly all toxic effects worsen as the dose increases - it is considered essential for proving that the agent causes the effect.

Even the smallest dose that the team applied resulted in alleged effects on the rats. That is sometimes seen with other toxic agents. The team suggests that the effect kicks in at some very low dose, hits its maximum extent immediately, and stays the same at any higher dose.

But it could more simply mean the GM maize and the herbicide had no measured effect, and that is why the dose made no difference. "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."

Why would scientists do this?
The research group has long been opposed to GM crops. It claimed in 2010 to have found evidence of toxicity in tests by the GM-crops giant Monsanto of its own Roundup-resistant maize. Other toxicologists, however, said the supposedly damning data revealed only insignificant fluctuations in the physiology of normal rats.

French blogger Anton Suwalki, who campaigns against pseudoscience, has a long list of complaints about the group, including what he calls "fantasy statistics".

And who funded the work?
The group was funded by the Committee for Research and Independent Information on Genetic Engineering, or CRIIGEN, based in Paris, France. The lead author on today's study, SÚralini, is head of its scientific board, and it pledges to "make every effort towards the removal of the status of secrecy prevailing in genetic engineering experiments and concerning genetically modified crops (GMOs), both being likely to have an impact on the environment and/or on health".

Don't they realise that other scientists criticise their methods?
They might. The paper is supposed to have been reviewed by other scientists before it was allowed for publication. But the team refused to allow journalists to show the paper to other scientists before the news reports were due to be published.

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