Send Add comment

Long-term feeding study with rats

New study of GM maize is controversial in scientific circles

According to the results of a long-term feeding study at the University of Caen in France, genetically modified NK603 maize and the herbicide Roundup lead to severe health problems in rats. However, the results are disputed in scientific circles. Other scientists have questioned the experimental design and the statistical analysis and claim the type of rat used in the experiment was unsuitable. Despite this, three French ministers have called on the European Commission to act, mentioning an emergency suspension of the import licence for NK603 maize as a possible option.


GM maize and the herbicide Roundup are said to lead to increased cancer and kidney damage in rats, according to the interpretation of a new feeding study.

Source: Wikimedia commons

Gilles-Eric Seralini

Gilles-Eric Seralini of the University of Caen is head of the research team that conducted the latest feeding experiments with GM maize.

Source: Universität Caen

The research team led by Gilles-Eric Seralini at the University of Caen presented its research findings on the potential health risks of NK603 maize to the press on 19 September. The paper will shortly be published in the journal Food and Chemical Toxicology. NK603 is a GM maize variety produced by Monsanto that is resistant to the active herbicide ingredient glyphosate. It has been authorized for food and feed use in the EU since 2004, but not for cultivation.

Two-year experiment instead of 90-day test

Gilles-Eric Seralini’s team conducted feeding experiments with rats over the entire lifespan of the animals, which was around two years. Generally, feeding experiments to investigate the health risks of GM plants last no more than three months. A large number of experts are of the opinion that longer feeding studies do not provide any more information, partly because the animals do not receive a balanced diet.

The scientists in Caen observed ten groups of 20 rats (ten males and ten females), each of which was fed a different diet:

  • Three groups received food consisting of 11 per cent, 22 per cent or 33 per cent NK603 GM maize.

  • Another three groups received the same food, but with maize that had previously been treated with Roundup.

  • Finally, three groups were given water containing Roundup. The highest dose is said to be the same as the maximum permitted threshold for Roundup in GM food in the US.

  • The tenth group was the control group, which was fed only on conventional maize and water with no herbicide.

According to Seralini, the GM maize and Roundup, which contains glyphosate, produced similar problems in the trial animals. 50 per cent of the male rats and 70 per cent of the female rats died prematurely. Only 30 per cent and 20 per cent of the males and females in the control group died prematurely. The main cause of the higher mortality rate in the female rats was breast cancer, while the male rats died of liver and kidney damage and skin cancer. 17 months after the start of the trial, five times more animals had died in the group fed on GM maize than in the control group. Seralini interprets the findings as a clear indication that the herbicide and the substances in the GM maize disrupt the animals’ hormonal system, triggering organ damage and cancer. He finds the results alarming.

Study results disputed – are the results invalid?

A number of scientists have already severely criticised the study. They claim that the results may not be at all suitable for identifying potential health risks associated with NK603 or Roundup. Independent British scientists like Prof. David Spiegelhalter (University of Cambridge), Prof. Maurice Moloney (Rothamsted Research) and Prof. Anthony Trewavas (University of Edinburgh) view the experimental design, the statistical analyses and the published data as inadequate:

  • The animals used in the experiment (Sprague Dawley rats) are naturally very prone to cancer. More than 70% develop cancer within two years anyway.

  • The small number of animals used in the experiment was also criticised in this context. The control group, which was fed only on conventional maize and water without herbicide, consisted of only ten animals. This is claimed to be inadequate for a statistically secure analysis of the experiments. For this they would have needed 90-180 rats. On this basis, the observed number of rats in the control group that displayed effects is more likely the result of random variation and does not allow conclusions to be drawn from the observed differences in the other trial groups.

  • The observed health problems in the trial animals did not increase in line with higher levels of GM maize or herbicide in the food, which you would normally expect if the effects were caused by certain substances in the food. Seralini’s critics claim he has not provided a sufficient explanation for this in his study. In some cases, the most severe effects occurred in rats that received the lowest dose. Some of the rats fed GM maize or water with herbicide actually survived better than those in the untreated control group.

  • The food used in the experiment has also been criticised. Because of the high maize content, scientists claim it is not balanced enough for a healthy diet and is therefore unsuitable for a long-term experiment. Neither did the study provide any data to show how much food the animals had actually eaten. The rat line they used is known to be more prone to tumours when the rats are fed large amounts of food.

  • The study does not provide any data on the precise composition of the food. For instance, mycotoxin contamination cannot be ruled out. Mycotoxins could also have triggered the health problems observed in the study.

In addition, Mark Tester of the Australian Centre for Plant Functional Genomics (University of Adelaide) describes the statistical analyses used in the study as “unconventional”. Since there was no defined data analysis plan, he suspects the scientists fished around in the data once the study ended until they found something interesting. Many of the data from the feeding experiments were missing from the paper, as were statistical values like the range of variation of the test data. This makes it difficult for external scientists to follow the conclusions drawn by Seralini and his colleagues.

Seralini drew attention to himself in 2007 with study results that he claimed pointed to health risks associated with genetically modified MON863 maize. This research was partly financed by Greenpeace. After evaluating his study results, the European Food Safety Authority (EFSA) and the German Federal Office of Consumer Protection (BVL) concluded that the results presented by Seralini did not provide any evidence of health risks.

EFSA to examine study, politicians call for ban

The European Commission has asked the European Food Safety Authority to assess the study. If new findings come to light concerning health risks, the Commission will take appropriate action. Germany’s Federal Institute for Risk Assessment (BfR) and Federal Office of Consumer Protection and Food Safety (BVL) have also said that they intend to examine the study in more detail before commenting.

However, politicians in France want to see faster reactions. MEP Corine Lepage called on the Commission to suspend authorisation of NK603 and to conduct long-term studies for other GM plants that have been authorized in the EU. In a joint communication, French Minister for Agriculture Stéphane Le Foll, Environment Minister Delphine Batho, and Minister for Health and Social Affairs Marisol Touraine also called on the Commission to act quickly to “protect human and animal health”, saying that an emergency suspension of the import authorisation for NK603 might be appropriate.

Alexander Bonde, Baden-Württemberg’s Minister for Consumer Affairs and Chairman of Germany’s Conference of Agricultural Ministers, intends to include the issue on the agenda of the Conference of Agricultural Ministers in the next few weeks so that they can discuss the potential consequences.

Discussion / Comments

Comments are being loaded…