A controversial French study linking GM corn to cancer has been pulled apart by Kiwi scientists and others overseas.
The study has led the French Government to order an investigation and GE Free New Zealand has requested an "immediate review" by Food Standards Australia New Zealand on the GE food the authority has approved for the food chain. But the findings have also been challenged by experts around the world.
Researchers at the University of Caen analysed the effects of NK603, a type of herbicide-tolerant corn developed by US firm Monsanto, on rats.
The study concluded female rats fed the maize developed large mammary tumours more often than, and before, untreated rats used as controls. Male rats presented with more large tumours than the control group.
But yesterday, scientists cited "major flaws" in the study, criticising the size of the test groups and questioning the link between treatment and effect.
Mark Vickers, a senior research fellow at the University of Auckland, said he was surprised the paper was published without key data gauging fluid intakes and body growth.
Dr Vickers said the strain of rat used in the trials was prone to developing tumours with advancing age anyway.
University of Auckland professor of biostatistics Dr Thomas Lumley believed the strongest conclusion that could be drawn from the study was that it would be worth studying a larger group of controls, and just a single low dose of Roundup or GM corn.
But Organic New Zealand spokeswoman Debbie Stanwick said she would not be surprised if the claims were genuine.
"You can't keep putting something which isn't natural and has been doused in herbicide into your body - it's not rocket science."
* Rats in groups of 10 were tested over two years with maize genetically modified to be tolerant to the herbicide Roundup.
* Females fed the maize developed large mammary tumours almost always more often than and before untreated rats used as controls.
* "I do not think the herbicide risks look convincing, especially with respect to cancer." - Thomas Lumley, University of Auckland.
* "I am surprised it was accepted for publication." - David Spiegelhalter, University of Cambridge.