As the debate over GM products rages on, help for their proponents may come from an unlikely source. Arpad Pusztai achieved notoriety in the UK for bringing some of the worries over GM products to public attention following experiments with GM potatoes. However, speaking recently at the Organic Food and Wine Festival in London, he made it clear that he is not anti-GM per se. Instead he believes that testing has not yet been rigorous enough to prove the case one way or the other.

Dr Pusztai argued that the main studies used in the past to show the safety of GM food were technically flawed. The US Food and Drug Administration tested Flavr-Savr tomatoes on rats and found no change in weight gain, food consumption or clinical chemistry against rats eating non-GM produce. This test was used as a basis for saying that all GM food is safe, Dr Pusztai claimed.

However, he said the test was flawed because the tomatoes were grown at a different location and at different times, there were differences in the rats' starting weights, invalidating the findings, and the results were never published and peer-reviewed. In addition, he claimed a number of rats died unexpectedly after the tests. He had similar concerns over Japanese tests on mice and soybeans.

Dr Pusztai's solution is based on work he is developing and involves more rigorous testing techniques. He said that tested animals need to be of the same weight and age, preferably young so that changes in their metabolism and immune system can be tracked. The parent and GM crop should be identical, except for the genetic change. Rats should be weighed throughout. He added that as tests progressed, they needed to be extended to female rats and human volunteers.

"The only hope for GM foods in the 21st century is that we throw out crude methods of altering crop genomes," he concluded. "We need to use more refined replacement methods and then subject them to rigorous, proper testing before deciding if they are safe." The debate over the safety of GM foods is a long way from being over.

By Hugh Westbrook, just-food.com correspondent