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GM health risks



Key Information

From the beginning industry and governments around the world have overstated the benefits of GM crops whilst downplaying the risks that GM crops pose to the environment, human and animal health. In their desperate attempt to force GM food into the supermarkets the GM lobby focuses on PR spin rather than scientific studies to persuade sceptical consumers that GM food is safe to eat. The argument that GM food is safe is based more on wishful thinking rather than actual science.

Scientists are still a very long way from truly understanding the DNA and genes of living things. As a result it is impossible to tell what the long-term health implications of GM food will be. Genetic engineering can introduce proteins that humans have never been exposed to before. In addition, the modification process could have caused an increase in the level of existing allergens (a substance that can cause an allergic reaction). For example, one GM soya had 27% more allergens than non-GM soya.

There are concerns that GMOs could pose a serious health risk, with possible health problems ranging from antibiotic resistance, the creation of new toxins, and unexpected allergic reactions. These concerns remain largely speculative because no one can predict what the outcome of the introduction of GMOs into the food chain will be since:

  • no adequate safety tests have been carried out

  • no-one is monitoring the impact of GMOs into the diets of those countries now selling significant quantities of GM

  • far too little is known about genes and DNA to predict what the possible unexpected effects of genetic engineering will be


Lack of safety testing

No one is monitoring the risks to human health

Despite massive public concern GM foods have undergone little rigorous and no long term safety testing. The GM industry likes to claim that Americans have eaten GM foods for years with no ill effects. However this is not backed up with any studies. GM foods are unlabelled in the US and no one has monitored the consequences, for example allergic or carcinogenic reactions. Any health effects from a GM food would have to meet unusual conditions before they would be noticed. If GM foods caused a rise in common or slow-onset diseases like allergies or cancer, nobody would know what caused the rise.

In the UK no GM crops are being grown on a commercial basis and there are only a few GM derived food products on the shelves. But millions of tons of GM soya, oilseed rape and maize are imported every year and fed to our farm animals. This raises serious questions about the impacts on animal health and those consuming the milk, meat and eggs - products which do not have to be labelled. There has been little long-term safety testing for GM animal feeds. Laboratory studies and anecdotal reports from farmers show that GM feed can disturb animals' body functions and make them ill. We also know that GM DNA in feed is taken up by the animal's organs. Small amounts of GM DNA appear in the milk and meat that people eat. 123

Professor Bob Orskov OBE, director at the International Feed Resource Unit in Aberdeen, is among those who have warned about the lack of proper testing: "As a scientist, I wouldn't drink milk from cows fed GM maize with the present state of knowledge"4


Safety testing based on flawed science

"The possibility that certain novel genes inserted into food may cause problems to humans is a real possibility, and 'substantial equivalence' is a rule which can be used to evade this biological fact." British Medical Association, 1999

"There is no unique, absolute, scientific cut-off threshold available to decide whether a GM product is safe or not". Leaked European Commission document submitted to the World Trade Organisation

The biotech industry likes to claim that GM foods are the "most tested" foods in history. But GM foods are not properly tested for human safety before they are released for sale. In fact the only study ever published on the direct effects on humans of eating a GM food found potential problems but was never followed up.5

Current safety tests are based on a flawed model of how genetic modification affects an organism. Genetic modification is a crude and imprecise way of incorporating foreign genetic material (e.g. from other plants, animals, viruses and bacteria) into crops, with unpredictable consequences for how the foreign genes will express themselves and affect the functioning of other genes in the plant. 67

For GM crops and food products to be considered safe, all a GM company needs to show is that the new plant or product is largely similar to one already considered safe. Just a few key chemicals such as nutrients and known toxins are compared to those in the non-GM plant. If the levels are similar, then the whole plant is considered to be 'substantially equivalent'. This ignores mounting scientific evidence that inserting foreign genes will often lead to unexpected results such as new toxins, changed levels of plant chemicals or new allergens.

The concept of substantial equivalence was introduced in the early 1990s to facilitate rapid approval for genetically modified foods and has enabled the GM industry to avoid the need to carry out thorough safety testing of GM foods. The stringent testing normally required for new food products can cost millions of pounds and take years of testing before a product gains approval for marketing. Such demands and delays would have made genetically modified foods unprofitable for private companies.

On top of that there is a lack of clear and universal guidelines about what to test and just how similar the properties of the natural and the GM plant need to be. The tests for equivalence are generally carried out by the researchers or Biotech company wanting to grow the GM plant. Independent research is systematically blocked by the GM corporations which own the GM seeds and reference materials. This is illustrated by the example of Professor Bela Darvas of Debrecen University, Hungary, who was refused more Mon 810 corn to use in his studies after informing Monsanto that the variety was lethal to three Hungarian insect species.8

Whether a GM food is judged safe or not depends on tests conducted by the GM companies themselves. Most of these tests have never been published or subjected to independent peer review. For example, a Spanish researcher who investigated this in 2000 could find only eight published safety studies on food from different GM crops9, but there are over 40 GM crops approved for sale around the world.

Professor Janet Bainbridge, Chair of the Advisory Committee on Novel Food & Processes commented that '"current regulation in the UK appears so far to have protected the public from any potential hazards of GM foods. However, we do not know what we may have missed. The presumption of safety of novel GM plants on the basis of substantial equivalence lacks scientific credibility, given modern expectations of standards of evidence."10


Risks to your health

Studies on animals combined with on-the-ground experience with GM crops over the last ten years show that GM technology is not as safe as its advocates claim. The results of this research make alarming reading because they are the opposite to the assumptions used in current testing of GM foods. This means that the safety of both new GM foods and those already currently on sale in shops is under question.


There are four main areas of food safety concern:

Toxicity - When a crop is changed to make it resistant to insects or tolerant of weedkillers, it has to make new compounds to carry out these functions. Some of these new compounds can be toxic to human and animals. 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.


Allergies - Some of the new compounds produced in GM plants have been found to cause an allergic reaction. Allergic reactions affect only a small proportion of the population, but the consequences can be severe, even deadly. Once allergies have developed, there may be no safe level of exposure for the affected person. It is possible to test for allergic reactions if the GM genes come from something such as peanuts, which are known to cause allergies in some people, but with new sources this is much harder. The process of genetic modification itself can change the properties of a protein from neutral to immunogenic, as demonstrated by the transgenic pea (see below). None of the testing used for assessing the safety of transgenic plants by regulatory bodies would have detected such changes.


Unintended effects - 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. The process of genetic modification itself causes hundreds of mutations in the cells. Normal genes may be disrupted or the foreign genes may not function properly. This means that there is plenty of potential for unexpected outcomes affecting 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 may create 'super-bugs'. When GM plants are eaten, the foreign DNA can be taken up by the bacteria living in our guts. This is called horizontal gene tranfer. For years the GM industry claimed that this would not occur, but several study now show that it does.11 This poses very serious risks for our health.

Where GM plants contain genes for antibiotic resistance these can be taken up by gut bacteria. These may then turn into superbugs - bacteria that cannot be controlled by antibiotics.

The British Medical Association has called for a ban on the use of antibiotic resistance marker genes and the EU has recently introduced new rules banning the use of some, but not all antibiotic resistance genes.12

Where plants have been engineered to produce toxins to fend off pests, such genes may also be taken up by gut bacteria, which could then potentially start producing those toxins in our guts.13


Case studies

Case study - GM genes transferred to bacteria in human guts

The only human feeding study with GM to date was commissioned and funded by the Food Standards Agency. It involved seven human volunteers who ate GM soy to see if the DNA of the GM soy transferred to the human gut bacteria. The study found that three of the seven volunteers had transgenes from GM soy transferred into their gut bacteria.14

"This transgene was stable inside the bacteria and appeared to produce herbicide-tolerant protein... In the only human feeding study ever conducted on GM crops, long standing assumptions that genes would not transfer to human gut bacteria were overturned. The findings should prompt immediate comprehensive follow-up tests to determine the implications for health among both the general population and at-risk groups."15

On the market despite safety concerns

In some cases, testing has revealed potential problems with GM crops, but these findings have been ignored and the crops approved regardless.

Testing of Monsanto's GT73 oilseed rape revealed consistently higher levels of an anti-nutritional factor, but this was not investigated further. Feeding trial results were contradictory, with one study feeding GM meal to rats finding significant decreases in body weight, one finding an increase in liver weights, and one finding no differences. The only one which was submitted to the EU authorities was the one finding no differences.

Testing of Monsanto's MON863 maize on rats revealed significant differences in factors such as white blood cells, kidney weights and kidney structure. Monsanto initially refused to publish the rat study and had to be forced to do so in a court ruling in a case brought by the German Government. Member State concerns were again disregarded and the maize approved.

Case Study - GM DNA detectable in digestive tract of sheep

The fact that gene transfer can take place in the gut was backed up by another trial with sheep eating GM maize, which again found that some of the genetic material remained in the gut after ingestion, and was transferred to gut bacteria. 16

Case study - GM maize disturbs digestive systems of sheep

Sheep fed Bt insecticide-producing GM maize over three generations showed disturbances in the functioning of the digestive system of ewes and in the liver and pancreas of their lambs17.

Case study - Mice allergic to GM pea

In 2005 unexpected allergic lung damage occured in mice who were fed on a GM pest-resistant pea. This may have been caused by the expression of the protein in rather than the protein itself. This led the author to say that animal studies are needed.18

Case study - Bt cotton causes allergic reaction in workers

Since 2004, some cotton workers in India have been experiencing allergic reactions to genetically modified Bt cotton, but not to conventional varieties. The longer the workers are exposed to the genetically modified Bt cotton, the more severe their symptoms are. Allergic reactions range from mild to severe itching to red and swollen eyes. One doctor reported that he had seen approximately 150 cases of allergies to Bt Cotton in 2005, and another 100 in 2004.19

Case Study - Puztai and Ewen

In 1998 Scientists Árpád Pusztai and Dr Ewen found that rats fed on potatoes genetically modified to contain lectin developed immune system damage and other serious health problems. Even though the lectin itself caused no adverse effects their conclusion was that the GM process had somehow made the potatoes less nutritious. Pusztai felt he had a duty to speak out, "just to inject some caution into this business". Because of the controversial nature of the research, the data in this paper was seen by a total of six reviewers when presented for peer review; five of these reviewers judged the work acceptable.20 More than ten years on the GM lobby is still engaged in a campaign to discredit the research results.

Case study - GM food can have changed nutritional value

GM soya had 12-14% lower amounts of cancer-fighting isoflavones than non-GM soya21.

Oilseed rape engineered to have vitamin A in its oil had highly reduced vitamin E and altered oil-fat composition22.

Case study: Soybean with brazil nut gene triggers brazil nut allergies

In the mid 1990's Pioneer Hi-Bred began to genetically modify a soybean that would take a gene from a Brazil nut in the hopes that soy would increase the production of the amino acid methionine. Because it was known that many people are allergic to brazil nuts, Pioneer Hi-Bred decided to test the new GM soybean for allergens. To the company's surprise three separate tests all showed that individuals allergic to Brazil nuts were also allergic to the new GM soybean.23

Case Study: Tryptophan

In 1989, Showa Denko genetically engineered a bacteria to produce the food supplement tryptophan. This unexpectedly also produced trace amounts of a toxic dimerisation tryptophan product. In the first months of use 37 people died and 1500 became permanently disabled. It is believed several hundred more have since died. The GM product was a purified single chemical which had passed the required substantial equivalence testing. Some scientists arguing for extreme caution in dealing with genetically engineered foods point out that if the substance had caused delayed harm, such as cancer 20 years later there would have been no way to attribute the harm to the cause.242526



Unapproved GM maize contaminates food chain

Another risk to human health is the accidental contamination of our food with GM material that has not even been approved for human or animal consumption.

In April 2005 it was discovered that biotech company Syngenta had accidentally sold hundreds of tonnes of the unapproved GM maize seed Bt10 to US farmers for four years, mistaking for the approved variety Bt11. Bt10 contains a controversial antibiotic resistance gene, which confers resistance to an important group of antibiotics.

Around 1000 tonnes of the illegal GM maize had entered the European food chain. The incident raised concerns over the complacency of the biotech industry, lack of regulation in the US and breakdown in Europe's monitoring of food imports. Shipments of US maize contaminated with Bt10 have been found and impounded in Japan and Ireland.

For more information on allergicity of GM foods see: A critique of current allergenicity testing in the light of new research on transgenic peas, Foe, February 2006


GM - untested, unsafe, unwanted

An accumulating body of scientific evidence and on-the-ground experience with GM crops over the last ten years shows that this technology poses serious risks to human and animal health. With the availability of proven, energy-efficient and safe ways of meeting the current and future food needs of the world, GM crops are a waste of resources and a risk that is not worth taking


Take Action

Concerned about GM foods and GM animal feed? There are lots of things you can do either by yourself or as part of a group. Consumer pressure and public outrage stopped the commercial growing of GM crops in this country and took the majority of GM foods from the shelves. We can do the same with the remaining products and with GM animal feed.

  • Don't buy products that are labelled as derived from genetically modified organisms. Avoid animal products that are not clearly labelled as GM-free. If they are not labelled they will almost certainly have come from animals fed with GM feed. Buy organic -organic food must be GM-free and organic animal products must come from animals not fed with GM.

  • Start growing your own food - cheap, healthy and you know what's in it.

  • Tell your shops, supermarkets, dairy and meat producers that you do not want meat, dairy products and eggs produced from GM feed. Demand that they get GM feed out of their production lines and that they clearly label their products as GM-free so consumers can have confidence in what they are buying.

  • Buy from wholefood shops - almost all of them have pledged to be GM-free.

  • Have a look at our page on Taking Action for more ideas and action resources.


Find out more about the health risks of GM food:



1: Detection of genetically modified DNA sequences in milk from the Italian market. Agodi A. et al. Int J Hyg Environ Health, 209: 81-88, 2006.

2: Assessing the transfer of genetically modified DNA from feed to animal tissues. Mazza R. et al. Transgenic Res., 14: 775-784, 2005.

3: Detection of Transgenic and Endogenous Plant DNA in Digesta and Tissues of Sheep and Pigs Fed Roundup Ready Canola Meal. Mazza R. et al. J Agric Food Chem. 54: 1699- 1709, 2006.

4: Professor Orskov giving evidence at a 2000 public inquiry to examine whether Chardon LL should be added to the UK's National Seed List, http://www.rense.com/general4/gmsd.htm

5: PT Bernstein JA, Bernstein IL, Bucchini L, Goldman LR, Hamilton RG, Lehrer S, Rubin C & Sampson HA (2003). Clinical and laboratory investigation of allergy to genetically modified foods. Environmental Health Perspectives 111(8):1114-21

6: The Mutational Consequences of Plant Transformation. Latham J.R. et al. J Biomed Biotech. 2006, Article ID 25376, 1-7, 2006.

7: Transformation-induced mutations in transgenic plants: Analysis and biosafety implications. Wilson A.K. et al. Biotechnol Genet Eng Rev., 23: 209-234, 2006.

8: Hungary Bans GM Maize Seed Third World Network Biosafety Information Service February 1, 2005

9: Domingo, JL. 2000. Health risks of GM foods: many opinions but few data. Science 288 1748-9

10: Professor Janet Bainbridge, Chair of ACNFP, evidence to the Royal Society, 16 May 2001

11: Netherwood et al, "Assessing the survival of transgenic planic plant DNA in the human gastrointestinal tract," Nature Biotechnology 22 (2004):2.

12: EU regs on antibiotic markers

13: Fate of genetically modified maize DNA in the oral cavity and rumen of sheep.

Duggan P.S. et al. Br J Nutr., 89: 159-166, 2003.

14: Netherwood et al, "Assessing the survival of transgenic planic plant DNA in the human gastrointestinal tract," Nature Biotechnology 22 (2004):2.

15: Smith, Jeffery. Genetic Roulette: The Documented Health Risks of Genetically Engineered Foods, p.130, 2007

16: Fate of genetically modified maize DNA in the oral cavity and rumen of sheep.

Duggan P.S. et al. Br J Nutr., 89: 159-166, 2003.

17: A three-year longitudinal study on the effects of a diet containing genetically modified Bt176 maize on the health status and performance of sheep. Trabalza-Marinucci M. et al. Livestock Science, 113: 178-190, 2008.

18: Transgenic expression of bean alpha-amylase inhibitor in peas results in altered structure and immunogenicity. Prescott V.E. et al. J Agric Food Chem., 53: 9023-9030,2005.

19: Ashish Gupta, "Impact of Bt Cotton on Farmers' Health (in Barwani and Dhar District of Madhya Predesh)," Investigation Report, October-December 2005.

20: Effect of diets containing genetically modified potatoes expressing Galanthus nivalis lectin on rat small intestine] The Lancet (Abstract) October 16, 1999, Pages 1353-1354

21: Alterations in clinically important phytoestrogens in genetically modified, herbicide-tolerant soybeans. Lappe M.A. et al. J Med Food, 1: 241-245, 1999.

22: Seed-specific overexpression of phytoene synthase: increase in carotenoids and other metabolic effects. Shewmaker CK et al. Plant J, 20: 401-412, 1999.

23: Julie A. Nordlee, "Identification of Brazil-Nut Allergen in Transgenic Soybeans," New England Journal of Medicine, 334 (1996):688-692.

24: Tryptophan produced by Showa Denko and epidemic eosinophilia-myalgia syndrome. National Center for Biotechnology Information (Abstract) October 1996

25: John B. Fagan (November 1997). "Tryptophan Summary". http://www.holisticmed.com/ge/trypt.html. Retrieved on 2006-10-27.

26: Toxic L-tryptophan: Shedding Light on a Mysterious Epidemic Seeds of Deception.com Comments by Scientists and Others.