Are genetically modified plant foods safe to eat?

Foodstuffs made of genetically modified crops that are currently available (mainly maize, soybean, and oilseed rape) have been judged safe to eat, and the methods used to test them have been deemed appropriate. These conclusions represent the consensus of the scientific evidence surveyed by the International Council for Science (ICSU) and are consistent with the views of the World Health Organization (WHO).

However, the lack of evidence of negative effects does not mean that new genetically modified foods are without risk. The possibility of long-term effects from genetically modified plants cannot be excluded and must be examined on a case-by-case basis. New techniques are being developed to address concerns, such as the possibility of the unintended transfer of antibiotic-resistance genes.

Genetic engineering of plants could also offer some direct and indirect health benefits to consumers, for instance by improving nutritional quality or reducing pesticide use.

Could genetically modified plant foods have health effects?

Millions of people worldwide have consumed foods derived from genetically modified plants (mainly maize, soybean, and oilseed rape) and to date no adverse effects have been observed.

Allergens and toxins occur in some traditional foods and can adversely affect some people leading to concerns that genetically modified plant-derived foods may contain elevated levels of allergens and toxins. Extensive testing of genetically modified food currently on the market has not confirmed these concerns. The use of genes from plants with known allergens is discouraged and if a transformed product is found to pose an increased risk of allergies it should be discontinued. All new foods, including those derived from genetically modified crops, should be assessed with caution.

One concern about food safety is the potential transfer of genes from consumed food into human cells or into micro-organisms within the body.
Many genetically modified crops were created using antibiotic-resistance genes as markers. Therefore, in addition to having the desired characteristics, these genetically modified crops contain antibiotic-resistance genes. If these genes were to transfer in the digestive tract from a food product into human cells or to bacteria, this could lead to the development of antibiotic-resistant strains of bacteria. Although scientists believe the probability of such a transfer is extremely low, the use of antibiotic-resistance genes has been discouraged.

Methods are now being developed whereby only the strict minimum of transgenic DNA is present in genetically modified plants. Some of these techniques involve the complete elimination of the genetic marker once the selection process has been made.

Several methods have been reported to create transformed plants that do not carry marker genes, for example co-transformation (Stahl et al., 2002), transposable elements (Rommens et al., 1992), site-specific recombination (Corneille et al., 2001) and intrachromosomal recombination (De Vetten et al., 2003). The International Maize and Wheat Improvement Center (known by its Spanish acronym, CIMMYT) is committed to providing resource-poor farmers in developing countries with the best options for implementing sustainable maize and wheat systems. CIMMYT believes that although GM crops will not solve all of the problems faced by farmers, the technology does have great potential and should be evaluated.

Scientists at CIMMYT have developed and adapted a transformation technique for wheat and maize to produce genetically modified plants that do not carry the selectable marker genes. With this technique, two DNA fragments, one containing the selectable marker gene and the other containing the gene of interest, are introduced and integrated separately into the genome. During the selection process, these genes segregate from each other, allowing the selection of the plants with only the gene of interest. CIMMYT scientists tested this simple technique using the selectable gene bar and the Bt genes, Cry1Ab and Cry1Ba, and successfully obtained plants without the selectable marker gene but with the Bt gene and which expressed high levels of Bt toxin. Transgenic plants were morphologically indistinguishable from untransformed plants and the introduced trait was inherited stably in the subsequent generations Efforts are now under way with the Kenya National Agricultural Institute and the Syngenta Foundation for Sustainable Agriculture to transfer these “clean events” to local varieties of maize in Kenya to provide resource-poor farmers with an additional option for insect control in the form they know best – the seed they plant. A similar approach is being used to enhance other important traits, such as abiotic stress tolerance and micronutrient content. Improved tolerance to stresses such as drought would directly benefit farmers, and biofortified plants could have a significant impact on children’s health in developing countries.

Other unintended changes

Other unintended changes in food composition can occur during genetic improvement by traditional breeding and/or gene technology. Chemical analysis is used to test GM products for changes in known nutrients and toxicants in a targeted way. Scientists acknowledge that more extensive genetic modifications involving multiple transgenes may increase the likelihood of other unintended effects and may require additional testing (ICSU, GM Science Review Panel).

Health benefits:

Potential health benefits of transgenic foods

Scientists generally agree that genetic engineering can offer direct and indirect health benefits to consumers (ICSU). Direct benefits can come from improving the nutritional quality of foods (e.g. Golden Rice), reducing the presence of toxic compounds (e.g. cassava with less cyanide) and by reducing allergens in certain foods (e.g. groundnuts and wheat). However, there is a need to demonstrate that nutritionally significant levels of vitamins and other nutrients are genetically expressed and nutritionally available in new foods and that there are no unintended effects (ICSU). Indirect health benefits can come from reduced pesticide use, lower occurrence of mycotoxins (caused by insect or disease damage), increased availability of affordable food and the removal of toxic compounds from soil. These direct and indirect benefits need to be better documented (ICSU, GM Science Review Panel).

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