http://www.economist.com/news/science-and-technology/21591159-study-suggested-gm-food-may-cause-cancer-has-been-retracted-smelling-rat


GENETICALLY modified maize causes cancer: that was the gist of one of the most controversial studies in recent memory, published in September 2012 by Food and Chemical Toxicology. Well, actually, it doesn’t. On November 28th the journal retracted it. This followed criticism that the rats used in the experiment were prone to cancer anyway; that the experimental protocol used could not distinguish tumours which might have been caused by GM food from those that were spontaneous (it had been set up to investigate a different question, and thus included too few animals); and that the authors offered no mechanism by which GM food could cause cancer. It would be too much to say that GM foods have thereby been proven safe. But no other study has found health risks in mammals from eating them.

The article was by Gilles-Eric Séralini of the University of Caen, in France, and his colleagues. It described what happened to rats fed with NK603 maize, a variety made resistant to a herbicide called glyphosate by a genetic modification made by Monsanto, an American firm. Monsanto also discovered glyphosate’s herbicidal properties. It sells it under the trade name “Roundup”. Because the crop is resistant to glyphosate, farmers can spray their fields with it, killing weeds but leaving the maize unscathed.

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In Dr Séralini’s experiment, rats fed with the modified maize were reckoned more likely to develop tumours than those which had not been. Females were especially badly affected: their death rates were two or three times as high as those of control groups. (Rats fed with diluted glyphosate also suffered health damage.)

The article was explosive. Jean-Marc Ayrault, France’s prime minister, said that if its results were confirmed his government would press for a Europe-wide ban on NK603 maize. Russia suspended imports of the crop. Kenya banned all GM crops. The article came out two months before a referendum in California that would have required the labelling of all GM foods. It played a role in the vote, though in the event the proposition was defeated.

The paper had all the more impact because it contradicted previous studies on GM foods. Research published in 2007 by Japan’s Department of Environmental Health and Toxicology on genetically modified soyabeans, for example, reported “no apparent adverse effect in rats” from the beans (or the glyphosate). That finding was confirmed by a review of all the evidence by a team at the University of Nottingham, in England, published in 2012.

But Dr Séralini’s paper was also explosive for reasons unrelated to its content. It stirred up controversy before it was even published because the authors insisted that journalists who were given advance copies could not seek independent comment on the contents when writing their articles, and would face a large fine if they did so. This was an unusual and widely criticised requirement, which had the effect of ensuring that third-party criticism of the paper did not appear during the important early days when a huge amount of public attention was focused on the findings. That may help explain the panicky reactions in France, Kenya and Russia.

Though the paper has been retracted, that is unlikely to be end of the matter. The journal’s publisher said there was “no evidence of fraud or intentional misrepresentation of the data”, which are the usual justifications for retraction. Scientific opinion runs strongly against the conclusion that GM foods are harmful—but not universally so. A group called the European Network of Scientists for Social and Environmental Responsibility backed Dr Séralini. And anti-GM activists are unabashed. In August a group in the Philippines destroyed a field study of Golden Rice, a type genetically modified to carry beta-carotene, a chemical precursor of vitamin A. Deficiencies of this vitamin contribute to the deaths of hundreds of thousands of children every year, and make many more blind. Neither the prospect of public-health benefits in poor countries, nor the absence of scientific evidence of damage to health is dulling the edge of the environmental campaign against all GM foods.

From the print edition: Science and technology