Smelling a rat - a study that suggested GM food may cause cancer has been retracted.

Smelling a rat

GM maize, health and the Seralini affair

The Economist - December 7, 2013

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, GM maize doesn't cancer and, on November 28th, the journal re­tracted the paper. This followed criticism that the rats used in the experiment were prone to cancer anyway; that the experimental pro­tocol used could not distinguish between tumours which might have been caused by gm food from those that were spontaneous (the experiment had been set up to investigate a different question and thus included too few ani­mals); and the authors offered no mechanism by which gm food could cause cancer. While it may be too much to say that gm foods have been proven to be safe for human consumption, no other study has found health risks in mammals from eating them.

The article was by Gilles-Eric Seralini of the University of Caen, in France, and his colleagues. It described what happened to rats fed with NK6O3 maize, a variety made by US firm Mon­santo and which was resistant to the herbicide glyphosate thanks to a genetic modification of the maize DNA. Monsanto also discovered glyphosate's herbicidal proper­ties, selling 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.

In Dr Seralini'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 NK6O3 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 from glyphosate). That finding was confirmed by a review of all the available evidence by a team at the University of Nottingham, in England, published in 2012.

But Dr Seralini'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 paper's 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 Seralini. And anti-GM activists are unabashed: in Au­gust, a group in the Philippines destroyed a field study of Golden Riceh had been 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.