Genetic engineering can cause unintended effects in plants. For example, genetic engineers have no control over where in a plant’s DNA their foreign genes will be inserted and often foreign genes are inserted in one of the recipient plant’s own genes, mutating it.

To my knowledge, it was never determined whether the GE tomato variety associated with lesions in rat stomachs had an unintentional insertional mutation or not.

While some scientists blamed the study methodology and argued against using animal feeding trials to assess GMOs, many FDA scientists questioned the safety of the tomatoes and the way the FDA management was handling the approval of GMOs. In a memo dated 16 June 1993 to Linda Kahl, Consumer Safety Officer at the FDA, Fred Hines, Staff Pathologist at the FDA wrote: “There is considerable disparity in the reported findings of gastric erosions or necrosis lesions from the three studies provided by Calgene Inc. This disparity has not been adequately addressed or explained by the sponsor or the laboratory where the study was conducted … The criteria for qualifying a lesion as incidental were not provided in the Sponsor’s report.”

In an October 1993 memo, the Director of Special Research Skills at the FDA suggested that the Flavr Savr safety experiments were “hardly strong evidence that gastric erosions are random and highly variable … the sponsor (Calgene) admits that no cause for the lesions is established … the data raise a question of safety”. The Additives Evaluation Branch added in December 1993 that “the responses Calgene provided were insufficient to answer the questions that still remain”.

In 1994, Dr Joseph Cummins, Emeritus Professor of Genetics at the University of West-Ontario warned that the inclusion in Flavr Savr tomatoes of a genetic sequence from the Cauliflower Mosaic Virus could create virulent new viruses. In October 1991, Dr Edwin Mathews from the Department of Health and Human Services and of the FDA’s Toxicology Group wrote to the FDA Biotechnology Working Group saying: “Genetically modified plants could also contain unexpected high concentrations of plant toxicants”.

The FDA was obliged to reveal these internal views in 1998 only after a lawsuit filed by consumer groups, scientists and others (Alliance for Bio-integrity) in which it was accused of ‘failing to fulfil its regulatory duties’.