Health risks

The ability to genetically modify plants gives scientists unprecedented power to alter the composition of foods, so that they are resistant to weedkillers, produce their own pesticides inside the plant, have altered nutrient content, or produce new chemicals for use in industrial processes or pharmaceuticals. This raises the question: is GM food safe to eat?

Some argue that GM foods are tested more thoroughly than any other foods, while others believe that we have not tested them enough so would not know if there are problems. Although GM foods have been eaten in some countries for years, there has been no monitoring so hard evidence about their safety is in short supply. Members of the public are dependent on regulators to predict the effects of GM foods on health before they are allowed on the market and to prevent unauthorised crops from entering the food chain.

The first specific regulations for safety testing of GM foods became law in Europe in 1997. These were revised in 2003. To read more about how GM food is assessed for food safety read the regulations section of our website

There are five main areas of food safety concern:

The genetic modification itself may make the plant toxic when eaten, or alter its nutrient content in ways that may be harmful.
The weedkillers used with herbicide-tolerant GM crops may be harmful to people eating the crops or living in the area when the crops are sprayed.
The new GM characteristic may cause allergies.
If antibiotic resistance genes are used, they may increase problems with drug resistant diseases.
The GM process may have unintended effects on the plant, which may affect food safety.

Toxicity and altered nutrients - When a crop is changed to make it resistant to insects (Bt crops) or tolerant of weedkillers (herbicide tolerant crops), it has to make new compounds to carry out these functions. If people have not eaten such compounds before, they will need to be safety tested. Some toxicity testing is carried out using laboratory animals, which may detect very rapid effects but may not identify longer-term, more subtle health effects. GM crops being developed for industrial or pharmaceutical use will also make new chemicals, some of which will need to be kept out of the food chain altogether. A new generation of GM crops is also being developed with intentionally altered nutrient content. Enhanced nutrients can be harmful if the levels are too high or if they are consumed by certain groups of people, even if they are of benefit to others: this will pose new challenges for regulators. Other GM crops could become toxic due to changes in the way the plant grows in the environment (for example, by taking up toxic metals from the soil).

Herbicide residues - Herbicide-tolerant GM crops are sold as a package with the company's own-brand herbicide. They are designed to survive when the field is sprayed with the herbicide to kill the weeds. There are concerns that pesticide residues from the spraying may be harmful when eaten or that the spraying harms local people living near by. Herbicides are regulated, but increasing volumes are being used with GM crops (more sprayings and additional spraying with other types of chemicals) as herbicide-resistant superweeds develop. In 2015, the World Health Organisation's cancer agency classified glyphosate, the active ingredient in Monsanto's weedkiller RoundUp, which is blanket sprayed on RoundUp Ready GM crops, as a probable human carcinogen.

Allergies - The new compounds produced in the GM food may cause an allergic reaction. Food allergies are on the increase as we eat more varied diets with new ingredients. It will be possible to test for allergenicity if the GM genes come from something such as peanuts, which are known to cause allergies in some people, but with new sources it will be much harder. When a new food is introduced, it takes 5-6 years before allergies are recognised.

Unintended effects - GM is not a precise technique. There is no control over where genes are inserted among the plant's own genes. Many copies or fragments of genes can be included and the gene may even be inserted backwards. There is plenty of potential for unexpected outcomes if normal genes are disrupted or the foreign gene does not function properly. These may affect the chemical composition of the crop and the safety of the food derived from it. Until recently, GM food safety testing ignored the potential for unintended effects, and techniques to screen GM foods for 'surprise' effects are still in the development stage.

Antibiotic resistance - Antibiotic resistance genes are used as 'markers' in GM crops to indicate whether the genetic modification has been successful. The GM process is inefficient and only a small number of cells incorporate the foreign genes. Therefore, an antibiotic resistance gene is included and, if the genetic modification is successful, the plant cell will grow in the presence of the antibiotic - if not, it will die. If these genes are transferred to disease-causing organisms, they may compromise antibiotic treatment. The antibiotic marker genes have no function in the plant and could be removed, but this costs more. The British Medical Association has called for a ban on the use of antibiotic resistance marker genes.

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