Truth: Studies show that GM foods can be toxic, allergenic, or have unintended nutritional changes

Myth at a glance

Peer-reviewed studies have found that GM foods can have unintended toxic and allergenic effects and altered nutritional value. Such effects have even been found in industry’s own studies carried out in support of regulatory authorization.

Most animal feeding studies on GMOs are short-term or medium-term in length – too short to show long-term (chronic) effects such as organ failure, cancer, or reproductive problems.

What is needed are long-term and multi-generational studies on GMOs to see if the signs of toxicity commonly reported in shorter studies develop into serious disease. But such studies are not required by government regulators anywhere in the world.

Industry and regulators often dismiss findings of toxicity in animal feeding trials on GMOs by claiming they are “not biologically significant” or “not biologically relevant”. However, these terms have never been properly defined in the context of animal feeding trials with GMOs and are scientifically meaningless.

There are three possible sources of adverse health effects from GM foods:

  • The GM transformation process may produce mutagenic effects that can disrupt or alter gene structure, disturb normal gene regulatory processes, or cause effects at other levels of biological structure and function. These effects can result in unintended changes in composition, including new toxins or allergens and/or disturbed nutritional value
  • The GM gene product – for example, the Bt toxin in GM insecticidal crops – may be toxic or allergenic
  • Changes in farming practices linked to the use of a GMO may result in toxic residues – for example, higher levels of crop contamination with the herbicide Roundup are an inevitable result of using GM Roundup Ready crops.

Evidence presented below and in Chapters 4 and 5 suggests that problems are arising from all three sources.

Unintended changes in composition

GM crops have been shown to have a different composition to their non-GM counterparts (see Myth 2.1) even when the two crops are grown under the same conditions, at the same time and in the same location – meaning that the changes are not due to different environmental factors but to the genetic modification.

Altered nutritional value is of concern for two reasons: first, because it could directly affect the health of the animal or human being that eats the food through providing an excess or shortage of certain nutrients; and second, because it is an indicator that the GM process has altered biochemical processes in the plant. This could be a clue that other unexpected and as yet unidentified changes have also occurred that might impact human or animal health, such as altered toxicity or allergenicity.

Toxic effects and signs of toxicity in laboratory and farm animal feeding studies with GMOs

Feeding studies on laboratory and farm animals show that GM foods can be toxic or allergenic. In these studies, a GM diet was fed to one group of animals and a non-GM diet was fed to a control group. The studies found signs of toxicity or actual toxic effects in the GM-fed animals, meaning that the GM foods tested were more toxic or allergenic than the non-GM foods.

Of the findings listed below, some are from experiments conducted by independent academic researchers and others by GM industry employees or contractors.

Severe organ damage and increased rates of large tumours and mortality

Rats fed Monsanto’s GM maize NK603 and tiny amounts of Roundup herbicide, which the maize is engineered to tolerate, over a long-term two-year period developed severe liver and kidney damage, disturbance to pituitary gland function, and hormonal disruption. Additional unexpected findings included increased rates of large palpable tumours and premature death in some treatment groups.1

This study came under heavy attack by pro-GM critics and was retracted by the journal that published it, over a year after it had passed peer review and appeared in print. However, the retraction was condemned as invalid by hundreds of scientists worldwide.2,3 A full discussion of this study and its retraction can be found below (Myth 3.2).

Altered blood biochemistry, multiple organ damage, and potential effects on male fertility

Rats fed the GM Bt maize MON810: Ajeeb YG (a variety developed by Monsanto for the Egyptian market) for 45 and 91 days showed differences in organ and body weights and in blood biochemistry, compared with rats fed the non-GM parent variety grown side-by-side in the same conditions. The authors noted that the changes could indicate “potential adverse health/toxic effects”, which needed further investigation.4

Histopathological investigations by the same group of researchers found toxic effects in multiple organs in rats fed the GM Bt maize for 91 days. Effects included abnormalities and fatty degeneration of liver cells, congestion of blood vessels in kidneys, and excessive growth and necrosis (death) of intestinal structures called villi. Examination of the testes revealed necrosis and desquamation (shedding) of the spermatogonial cells that are the foundation of sperm cells and thus of male fertility.5

Stomach lesions and unexplained mortality

Rats fed GM tomatoes over a 28-day period developed stomach lesions (sores or ulcers).6,7 There was unexplained high mortality in GM-fed rats: seven out of 40 rats fed GM tomatoes died within two weeks of the start of the experiment.8 This tomato, Calgene’s Flavr Savr, was the first commercialized GM food. The study, commissioned by Calgene itself, was never peer-reviewed and published and was only forced into the public domain by a lawsuit brought by a public interest group, the Alliance for Bio-Integrity, against the US Food and Drug Administration (FDA).9

The director of the FDA’s Office of Special Research Skills concluded that Calgene’s data fell short of “a demonstration of safety” or a “demonstration of reasonable certainty of no harm”,10 the typical standard expected of foods.

A “repeat” study performed by Calgene found lesions in non-GM fed animals as well as GM-fed animals. However, the study was not in reality a repeat but used tomatoes that had been prepared in a different way, which could affect the results, as noted by Fred Hines, the FDA pathologist. Hines concluded that Calgene had not provided enough data to justify its claim that the lesions seen across all the experiments were “incidental” and not due to the GM tomato.6

These studies and their implications have been discussed in detail in peer-reviewed articles by Dr Arpad Pusztai, a leading expert in animal feeding studies, and his research colleagues.8,11 Pusztai concluded, “The FDA’s conclusion that Flavr Savr presented no more dangers to consumers than ordinary tomatoes does not … appear to rest on good science and evidence which could stand up to critical examination.”11

Immune response and allergic reaction

Mice fed GM peas engineered with an insecticidal protein (alpha-amylase inhibitor) from beans showed a strong, sustained immune reaction against the GM protein. Mice developed antibodies against the GM protein and an allergic-type inflammation response (delayed hypersensitivity reaction). Also, the mice fed on GM peas developed an immune reaction to chicken egg white protein. The mice did not show immune or allergic-type inflammation reactions to either non-GM beans naturally containing the insecticide protein, to egg white protein fed with the natural protein from the beans, or to egg white protein fed on its own.12

The findings showed that the GM insecticidal protein acted as a sensitizer, making the mice susceptible to developing immune reactions and allergies to normally non-allergenic foods.12 This is called immunological cross-priming.

The fact that beans naturally containing the insecticidal protein did not cause the effects seen with the peas that expressed the GM insecticidal protein indicated that the immune responses of the mice to the GM peas were caused by changes in the peas brought about by the genetic engineering process. In other words, the insecticidal protein was changed by the GM process so that it behaved differently in the GM peas compared with its natural form in the non-GM beans – and the altered protein from the GM peas stimulated a potent immune response in the mice.12

T. J. Higgins, one of the researchers on the original study, subsequently co-authored a second, more recent study,13 which he claimed14,15 resolved concerns raised by the first study.12

But this claim is unfounded, as the two studies used markedly different methodologies to evaluate immune reactions. In the first study (Prescott and colleagues, 2005), the food was fed to the mice intragastrically (into the stomach), an approximation of human dietary exposure; then the mice were tested for allergic reactions.12

In the second study (Lee and colleagues, 2013), the GM and non-GM test proteins were first injected into the abdomen of the mice (intraperitoneal immunization) or introduced into their noses (intranasal immunization). Only after this procedure were the mice fed intragastrically with GM peas and non-GM beans containing the test proteins. Then the mice were tested for allergic sensitization. The result: both GM peas and non-GM beans were found to be equally allergenic.13

However, these allergic reactions to both the GM and non-GM test proteins are not surprising, because the mice had already been immunologically pre-sensitized to these products by the intraperitoneal and intranasal immunization procedures conducted prior to their being fed these products.

Therefore the second study (Lee and colleagues, 2013)13 does not contradict or disprove the the allergenic potential of the protein in the GM peas found in the first study12 in any way. Instead, the second study (Lee and colleagues, 2013)13 shows that it is possible to induce an allergic response to either GM peas or non-GM beans by pre-immunizing the mice to the proteins in a way that is very different from the usual way an animal or human is exposed to a food.

Immune disturbances

Young and old mice fed GM Bt maize for periods of 30 and 90 days respectively showed a marked disturbance in immune system cells and in biochemical activity. An increase of serum cytokines (protein molecules involved in immune response) after Bt maize feeding was also found, an effect associated with allergic and inflammatory responses.16

A study in rats fed GM Bt rice for 28 or 90 days found a Bt-specific immune response in the non-GM-fed control group as well as the GM-fed groups. The researchers concluded that the immune response in the control animals was due to their inhaling particles of the powdered Bt toxin-containing feed consumed by the GM-fed group. They recommended that for future tests involving Bt crops, GM-fed and control groups should be kept separate.17 This indicates that animals can be sensitive to small amounts of GM proteins, so even low levels of contamination of conventional crops with GMOs could be harmful to health.

Enlarged lymph nodes and immune disturbances

Mice fed for five consecutive generations with GM herbicide-tolerant triticale (a wheat/rye hybrid) showed enlarged lymph nodes and increased white blood cells, as well as a significant decrease in the percentage of T lymphocytes in the spleen and lymph nodes and of B lymphocytes in lymph nodes and blood, in comparison with controls fed with non-GM triticale.18 T and B lymphocytes are white blood cells involved in immunity.

Disturbed liver, pancreas and testes function

Mice fed GM soy showed disturbed liver, pancreas and testes function. The researchers found abnormally formed nuclei and nucleoli (structures within the nuclei) in liver cells, which indicates increased metabolism and potentially altered patterns of gene expression.19,20,21

Liver ageing

Mice fed GM soy over a long-term (24-month) period showed changes in the expression of proteins relating to hepatocyte (liver cell) metabolism, stress response, and calcium signalling, indicating more acute signs of ageing in the liver, compared with the control group fed non-GM soy.22

Disturbed enzyme functioning in kidney and heart

Rabbits fed GM soy showed enzyme function disturbances in kidney and heart.23

Higher density of uterine lining

Female rats fed GM soy for 15 months showed significant changes in the uterus and ovaries compared with rats fed organic non-GM soy or a non-soy diet. The number of corpora lutea, structures that secrete sex hormones and are involved in establishing and maintaining pregnancy, was increased only in the GM soy rats compared with the organic soy-fed and non-soy-fed rats. The density of the epithelium (lining of the uterus) was higher in the GM soy-fed group than the other groups, meaning that there were more cells than normal.

Certain effects on the female reproductive system were found with organic soy as well as GM soy when compared with the non-soy diet, leading the authors to conclude that there was also a need for further investigation into the effects of soy-based diets (whether GM or non-GM) on reproductive health.24

Severe stomach inflammation and heavier uteri

A feeding study in pigs fed a mixed diet containing GMO soy and maize over an average commercial lifespan of 22.7 weeks found that the GM-fed pigs had more severe stomach inflammation than pigs fed an equivalent non-GM diet and 25% heavier uteri, which could be an indicator of pathology.25 GM-fed pigs had a higher rate of severe stomach inflammation, 32% for GM-fed pigs compared to 12% for non-GM-fed. The severe stomach inflammation was worse in GM-fed males compared with non-GM fed males by a factor of 4.0, and in GM-fed females compared with non-GM fed females by a factor of 2.2.

GMO proponents claimed that non-GM-fed pigs had more cases of mild and moderate inflammation than GM-fed pigs and that therefore the GM diet had a protective effect.26 However, this claim collapses when it is considered that many GM-fed pigs were moved up from the “mild” and “moderate” categories into the “severe” inflammation category, leaving fewer pigs in the “mild” and “moderate” categories.

The Australia/New Zealand GMO regulator FSANZ argued: “The authors have not provided convincing evidence that stomach inflammation was present. The stomach data, as presented, do not support the authors’ interpretation and conclusions because… The presence of ‘inflammation’ was determined by visual appearance (reddening) only, without any microscopic (histological) confirmation. This is not considered a reliable method for establishing the presence of true inflammation, because it relies solely on the colour of the tissue which can vary for many reasons.”27

The lead researcher on the study, Dr Judy Carman, replied: “FSANZ suggest that the reddening may not be due to inflammation without suggesting what else it may be due to.

“Furthermore, the veterinarian that assessed the stomach inflammation in our pigs has many years of training and experience with pigs and other animals, including years of experience in assessing inflammation in those animals. In contrast, we are not aware that anyone in FSANZ has any training or experience in assessing stomach inflammation in pigs. In fact, we are not aware that anyone in FSANZ has any clinical experience whatsoever, either as a medical doctor or as a veterinarian. Therefore, FSANZ is commenting well outside of its area of expertise.

“In essence, FSANZ is saying that a veterinarian (or doctor) cannot determine if an animal (or human) has inflammation of a tissue such as a foot or an eye or anything else, without cutting out a sample of the affected tissue and sending it to a laboratory for histology. This is absurd.

“Also, while FSANZ want histology for this feeding study, they do not want it for feeding studies conducted by the GM industry. In fact, FSANZ does not require any feeding studies to be conducted on any GM crop whatsoever before they assess the crop to be safe to eat.”28

Liver and kidney toxicity

A review of 19 studies (including industry’s own studies submitted to regulators in support of applications to commercialize GM crops) on mammals fed with commercialized GM soy and maize that are already in our food and feed chain found consistent signs of toxicity in the liver and kidneys. Such effects may mark the onset of chronic disease, but longer-term studies would be required to assess this more thoroughly. Such long-term feeding trials on GMOs are not required by regulators anywhere in the world.29

In a separate study, the same research group, led by Professor Gilles-Eric Séralini at the University of Caen, France, re-analyzed Monsanto’s own rat feeding trial data, submitted to obtain approval in Europe for three commercialized GM Bt maize varieties, MON863, MON810, and NK603. Séralini’s team concluded that the maize varieties caused signs of toxicity in liver and kidneys. They stated that while the findings may have been due to the pesticides specific to each variety, genetic engineering could not be excluded as the cause.30 The data suggest that approval of these GM maize varieties should be withdrawn because they are not substantially equivalent to non-GM maize and may be toxic.

As a result of their findings, Séralini’s team decided to replicate and extend Monsanto’s study on GM maize NK603.31 Whereas Monsanto had ended its study after just 90 days, Séralini’s experiment ran for two years.1 The results are described in Myth 3.2.

Changed level of fats in blood and signs of liver and kidney toxicity

Rats fed insecticide-producing MON863 Bt maize had different growth rates and higher levels of certain fats (triglycerides) in their blood compared with rats fed the control diet. They also showed changes in liver and kidney function, which could have been early indicators of disease. This study was a re-analysis of Monsanto’s rat feeding trial data on its own GM maize. The authors of the re-analysis stated that the findings did not allow a conclusion that MON863 maize is safe. They added that long-term studies were needed to investigate the consequences of these effects.32

Toxic effects on liver and kidneys and altered blood biochemistry

Rats fed GM Bt maize over three generations showed damage to liver and kidneys and alterations in blood biochemistry.33

Enlarged liver

Rats fed a Monsanto GM oilseed rape (canola) over four weeks developed enlarged livers, often a sign of toxicity. The US FDA allowed Monsanto to do another experiment, this time comparing the GM canola with a range of eight different canola varieties, thus widening the range of variation and obscuring any effects of feeding the GM canola. This allowed Monsanto to conclude that the canola was as safe as other canola varieties.34

Disturbances in digestive system and changes to liver and pancreas

Female sheep fed Bt GM maize over three generations showed disturbances in the functioning of the digestive system, while their lambs showed cellular changes in the liver and pancreas.35

Excessive growth in the lining of the gut

Rats fed GM potatoes for only ten days showed excessive growth of the lining of the gut similar to a pre-cancerous condition, as well as toxic effects in multiple organ systems.36,37

Intestinal abnormalities

Mice fed a diet of GM Bt potatoes or non-GM potatoes spiked with natural Bt toxin protein isolated from bacteria over two weeks showed abnormalities in the cells and structures of the small intestine, compared with a control group of mice fed non-GM potatoes. The abnormalities were more marked in the Bt toxin-fed group.38

This study shows that the GM Bt potatoes caused mild damage to the intestines. It also shows that Bt toxin protein is not harmlessly broken down in digestion, as GM proponents claim, but survives in a functionally active form in the small intestine and can cause damage to that organ.38

Altered blood biochemistry and gut bacteria, and immune response

Rats fed GM rice for 90 days had a higher water intake as compared with the control group fed the non-GM isogenic (genetically the same, except for the genetic modification) line of rice. The GM-fed rats showed differences in blood biochemistry and gut bacteria, as well as an immune response. Organ weights of female rats fed GM rice were different from those fed non-GM rice. The authors claimed that none of the differences were “adverse”, but they did not define what they meant by “adverse”. Even if they had defined it, the only way to know if such changes are adverse is to extend the length of the study, which was not done. The authors conceded that the study “did not enable us to conclude on the safety of the GM food”.39

Altered gut bacteria and organ weights

Rats fed GM Bt rice for 90 days developed significant differences as compared with rats fed the non-GM isogenic line of rice. The GM-fed group had 23% higher levels of coliform bacteria in their gut and there were differences in organ weights between the two groups, namely in the adrenals, testes and uterus.40

Less efficient feed utilization and digestive disturbance

A feeding trial in which salmon were fed Monsanto’s GM Bt maize MON810 revealed less efficient feed utilization, with reduced ability to digest protein and minerals, compared with salmon fed non-GM maize. Also, a localized immune response was observed in the intestines of the GM-fed fish. The analyses were conducted after 33 and 97 days of feeding.41

Fish are not considered relevant to assessing health risks in humans, as they have a different metabolism and digestive system. However, GMO proponents use studies in fish to claim that GM foods are as safe and nutritional for human and animal consumption as their non-GM counterparts.42 Thus by their standards, it is acceptable to cite a study in fish as indicating risk.

Masking statistical significance through the concept of “biological relevance”

Study findings such as those described above have made it increasingly difficult for GM proponents to claim that there are no differences between the effects of GM foods and their non-GM counterparts. Clearly, there are.

To sidestep this problem, GM proponents have shifted their argument to claim that statistically significant effects are not “biologically relevant”.

The concept of lack of biological relevance has been heavily promoted by the industry-funded group, the International Life Sciences Institute (ILSI), and affiliates to argue against regulatory restrictions on toxic chemicals.43 But increasingly, it is invoked by authors defending the safety of GM crops42 to argue that statistically significant observable effects in GM-fed animals are not important.

However, this argument is scientifically indefensible. Biological relevance with respect to changes brought about by GM foods has never been properly defined.

Most feeding trials on GM foods, including those carried out by industry to support applications for GM crop commercialization, are not long-term but short- or medium-term studies of 30–90 days. These studies are too short to determine whether changes in animals fed a GM diet are biologically relevant or not.

In order to determine whether changes seen in these short- to medium-term studies are biologically relevant, the researchers would have to:

  • Define in advance what “biological relevance” means with respect to effects found from feeding GM crops
  • Extend the study duration from short- or medium-term to a long-term period. In the case of rodent studies, this would be two years – the major part of their lifespan29
  • Examine the animals closely to see how any changes found in short- or medium-term studies progress – for example, they may disappear or lead to disease or premature death
  • Analyze the biological relevance of the changes in light of the researchers’ definition of the term
  • Carry out additional reproductive and multigenerational studies to determine effects on fertility and future generations.

Since these steps are not followed in cases where statistically significant effects are dismissed as not “biologically relevant”, assurances of GM food safety founded on this line of argument are baseless.

In parallel with asserting lack of “biological relevance”, a trend has grown of claiming that statistically significant effects of GM feed on experimental animals are not “adverse”.39 Again, however, the term “adverse” is not defined and the experiments are not extended to check whether any changes seen are the first signs of disease. So the term is technically meaningless.

GMO proponents should cease attempting to mask findings of statistically significant effects from GM crops through the use of poorly defined and scientifically indefensible concepts.

Misuse of “biological relevance” places public health at risk: Monsanto GM maize study

In 2007 a team led by Professor Gilles-Eric Séralini published a new analysis of a rat feeding study conducted by Monsanto with one of its GM maize varieties.

The maize, called MON863, was approved for food and feed use in Europe in 2005–2006.44 The Monsanto study was used to gain regulatory authorization for the maize, but it could not be scrutinized by independent scientists and the public because the raw data were kept hidden on claimed grounds of commercial confidentiality. Only after a court action in Germany forced disclosure of Monsanto’s data could Séralini and colleagues conduct their analysis.32

Séralini’s team found that according to Monsanto’s own data, rats fed GM maize over a 90-day period had signs of liver and kidney toxicity. Also, the GM-fed rats had statistically significant differences in weight from those fed non-GM maize control diets. The GM-fed females had higher concentrations of certain fats in their blood. Excretion of some minerals was disturbed in GM-fed males.32

However, the statistically significant effects found in Monsanto’s study were dismissed by the European Food Safety Authority (EFSA) in its favourable safety assessment of the maize. Without evidence, EFSA claimed that these effects were not “biologically meaningful”.45,46 Both EFSA and the Monsanto-sponsored scientists cited differences in response to the GM feed between male and female animals, implying that toxic effects should be the same in both sex groups before they could be taken seriously.29,47,48,49 This is scientifically indefensible, since some substances, especially those with hormone-disrupting properties, are known to have different effects on males and females.50,51

Séralini and colleagues commented on the dangerous trend of dismissing statistically significant effects by claiming lack of biological relevance in a 2011 review of the scientific literature assessing the safety of GM crops, stating: “The data indicating no biological significance of statistical effects in comparison to controls have been published mostly by [GM crop developer] companies from 2004 onwards, and at least 10 years after these GMOs were first commercialized round the world”. Séralini’s team called the trend a matter of “grave concern”.29

EFSA responds to criticism over use of “biological relevance”

After being subjected to years of criticism by independent scientists and a member of the European Parliament over its use of “biological relevance”,52,29,53 in 2011 EFSA finally issued an Opinion on the relationship between statistical significance and biological relevance.54

But EFSA’s Opinion fails to give a rigorous scientific or legal definition of what makes a statistically significant finding “biologically relevant” or not. Instead, it allows industry to come to its own conclusion on whether changes found in an experiment are “important”, “meaningful”, or “may have consequences for human health”. These are vague concepts for which no measurable or objectively verifiable endpoints are defined. Thus they are a matter of opinion, not science.

Moreover, the lack of a sound definition of biological relevance means that regulators have no strong scientific or legal grounds to disagree with industry’s claim that a statistically significant finding is not biologically relevant. This, in effect, makes the GMO impossible to regulate.

The conclusions of the EFSA Opinion are not surprising, given that it is authored54 by several current or former affiliates of the industry-funded group, the International Life Sciences Institute (ILSI), including Harry Kuiper55 (also then the chair of EFSA’s GMO panel), Josef Schlatter, and Susan Barlow.56,57 ILSI is funded by GM crop developer/agrochemical companies, including Monsanto.58 Allowing ILSI affiliates to write EFSA’s scientific advice on how to assess the safety of GM foods and crops is akin to allowing a student to write his or her own examination paper or allowing scientists to review their own papers submitted for publication.

Masking statistical significance through the concept of “normal variation”

Studies often find statistically significant differences in the composition of GM foods compared with their non-GM counterparts. Studies also find statistically significant differences in animals fed a GM crop variety compared with animals fed the non-GM comparator variety.

However, GMO proponents consistently dismiss these statistically significant differences by claiming that they are “within the normal range of biological variation”.

This claim was made by Snell and colleagues in their review of animal feeding studies on GMOs. The review included some of the studies summarized in this report, which found significant differences in the GM-fed animals. In spite of this, the reviewers (in some cases reflecting the opinion of the authors of the original studies) used the concept of normal variation to conclude that “GM plants are nutritionally equivalent to their non-GM counterparts and can be safely used in food and feed”.42

It is scientifically unjustifiable to dismiss statistically significant changes in the GM-fed animals on the basis that they are within the normal range of variation. GMO proponents define the “normal range of variation” by collecting so-called “historical control data” from the control animals in many different studies carried out at different times, using different experimental conditions and measurement methods. The result is a set of numbers that vary widely, which appears to be the GM proponents’ objective. By using a dataset with such an unjustifiably wide range of variation, GM proponents are able to hide the differences in the animals fed the GMO under test and the non-GM control in the “noise” introduced by the irrelevant data.

However, there is no scientific justification for gathering disparate “historical control data” into the same dataset, and even less justification for comparing this sham dataset to the GMO of interest. On the contrary, this practice runs counter to the aim of scientific experiments, which are designed to minimise variables. According to rigorous scientific practice, in any single experiment, the scientist manipulates just one variable in order to test its effect. In this way, any changes observed can be traced to a probable single cause.

The scientific approach in an animal feeding trial designed to find out if a GMO is safe to eat is to ensure that the GMO is the single manipulated variable. One group of animals, the “treated” group, should be fed a diet containing the GMO. Another group, the control group, should be fed a similar diet, with the only difference being that it has not been subject to the genetic modification. All conditions of the experiment outside the GM component of the treated group’s diet must be the same. Within this tightly controlled setup, any changes seen in the treated group are likely to be caused by the GM feed.

Therefore in any experiment to discover the effects of a GMO in an animal feeding trial, the most valid comparator is the control group within that same experiment, known as the concurrent control. This is because the animals in other “historical” experiments will be subject to many variables, such as differences in diet and contaminants in food, water and bedding, laboratory conditions, and animal genetics. Restricting comparisons to the concurrent control group should be the rule in experiments commissioned by the GM industry in support of regulatory authorization.

Limitation of many feeding studies on GM foods

A limitation of many feeding studies on GM foods conducted by industry and independent researchers alike is that they use a non-GM comparator other than the isogenic non-GM parent.

In evaluating the importance of this shortcoming in various studies, it is necessary to consider the aim of the study. Feeding studies performed for regulatory purposes are supposed to reveal whether a GM crop is toxicologically different from the same crop without the genetic modification. Such studies should therefore involve feeding the test animals with the GM crop and the controls with the same amount of the non-GM isogenic variety, which has the same genetic background without the genetic modification. To minimize variables, the two crops should be grown in the same location and conditions at the same time.

However, the GM industry often does not carry out its feeding studies in this way. It does not restrict itself to the non-GM isogenic variety as the comparator. Instead it introduces a number of non-GM diets consisting of a range of distantly related non-GM crops grown in different locations and conditions and at different times.31,59 This has the effect of obscuring any effects from feeding the GM diet amongst the “noise” of irrelevant diets.

Many independent studies on GM foods suffer from the same limitation, though for a different reason. The reason in this case is that researchers find it difficult to access GM seeds of a specific variety and the non-GM isogenic comparator, because the GM companies restrict access to these research materials.60,61

Nonetheless, it is important to put this limitation in its proper perspective. Industry studies conducted for regulatory authorizations should be required to use (but often do not) the specific GM variety under test and the non-GM isogenic comparator grown at the same time under the same conditions, because this is the only way to ascertain whether unintended changes have been introduced into the crop by the genetic modification process. It is the purpose of the regulatory safety assessment to find this out.

A study that does not observe these restrictions cannot answer that particular question. But it can answer other questions.

For example, a study comparing the effects of feeding Roundup Ready soy versus feeding a non-GM soy variety with different background genetics and grown in different environmental conditions provides information regarding the relative toxicity of the two soy varieties. It can show whether the GM soy is “substantially equivalent” to the non-GM soy, or not. But if the GM soy diet is found to be more toxic than the non-GM soy diet, the study will not be able to identify the genetic modification as the cause of the increased toxicity. It will not reveal whether the toxic effects observed from consumption of the GM crop feed arise from the GM transformation process, from Roundup herbicide residues, from compositional differences arising from the different background genetics, from the different environmental conditions in which the crop was grown, or from a combination of two or more of these factors. Further experiments would have to be carried out to answer these questions.

Double standards used in evaluating studies that find risk versus studies that conclude safety

The much-cited review of animal feeding studies with GMOs by Snell and colleagues concluded that GM foods were safe. However, many of the reviewed studies had the limitation that the non-GM comparator crop was not the isogenic or near-isogenic variety. This limitation was common to studies that concluded the GM food tested was safe and those that raised concerns. But in an example of the double standards that are often applied to studies that find a GMO is safe versus studies that raise concerns, Snell and colleagues accepted at face value the conclusions of safety while rejecting as unreliable the findings of risk and harm.42

Regulators do not require long-term tests on GMOs

In order to detect health effects caused over time in humans eating GM foods, long-term (chronic) animal feeding trials are needed. But currently, no long-term tests on GM crops or foods are required by regulatory authorities anywhere in the world. Reproductive and multigenerational tests, which are necessary to reveal any effects of GM crops or foods on fertility and future generations, are also not required.29

This contrasts with the testing requirements for pesticides, which are far more stringent. Before a pesticide can be approved for use, it must undergo long-term two-year and reproductive tests on mammals.32 Yet GM foods escape such testing, in spite of the fact that virtually all commercialized GM foods are engineered either to contain an insecticide or to tolerate being sprayed with large amounts of herbicide, so they are likely to contain significant amounts of pesticides (herbicides are technically pesticides).

The longest tests that are routinely conducted on GM foods for regulatory assessments are 90-day rodent feeding trials. In Europe, even these were not compulsory29 until 2013, when a new law was passed.62 Such 90-day rodent trials are only medium-term (subchronic) tests that correspond to around seven years in human terms, based on the three-year average life expectancy of the Sprague-Dawley rat63 and the current life expectancy of a human in the UK.64 They are too short to show long-term effects such as organ damage or cancer.65 In addition, too few animals are used in these industry tests to reliably detect harmful effects.

In spite of these serious shortcomings, statistically significant harmful effects have been found even in industry’s own 90-day rodent feeding trials. The most common effects observed are signs of toxicity in the liver and kidney, which are the major detoxifying organs and often the first to show evidence of chronic disease.29

These observations are consistently interpreted by GM proponents and regulators as “not biologically significant” or as “within the range of normal variation”. But as explained above, these claims are not science-based.

Stacked-trait crops are less rigorously tested than single-trait crops

Most GM crops currently on the market and in the approvals pipeline are not single-trait crops but stacked-trait crops. “Stacked-trait” means that several GM traits are combined in one seed. For example, GM SmartStax maize has eight GM traits: six for insect resistance (Bt toxins) and two for tolerance to different herbicides.

Biotech companies have resorted to developing multi-trait crops because of the failure of single traits. For example (see Chapter 5):

  • Pests have developed resistance to single Bt toxins
  • Bt crops have been attacked by secondary insect pests
  • Weeds have become resistant to glyphosate, the herbicide that most GM crops are engineered to tolerate.

Stacked-trait GM crops pose more risk than single-trait crops because of the possibility of unexpected interactions between the different GM genes introduced into the crop – and between the multiple introduced GM genes and the genes of the host plant. There is also the risk of combined effects resulting from interactions between multiple toxins and biologically active compounds that may be produced in the plant as a result of the introduction of multiple genes. Interactions with residues of pesticides used in conjunction with the GM crop add another dimension of complexity. In short, the addition of multiple traits to a single crop increases the risk of unexpected harmful effects.

However, stacked-trait GM crops are even less rigorously tested for possible health effects than single-trait GM crops. Since 2013 Europe has required 90-day toxicological testing in rats for single-trait GM crops, but not for stacked-trait crops. The European Food Safety Authority (EFSA) maintains that it can assess the toxicity of the final stacked-trait crop by looking at industry test findings on the single-trait crops that were used to develop it.66

This stance is based on a series of simplistic assumptions, not on empirical evidence. It fails to look at the actual effects of the combined mutational effects and the mixed transgenes and their products within the crop.

Antibiotic resistance genes could produce “superbugs”

An additional cause for concern regarding GM food safety is the potential presence of antibiotic resistant “marker” genes in the GM crop. These genes are included in the GM gene cassette to enable genetic engineers to see whether the GM gene of interest has been successfully integrated into the DNA the cells of the host plant. When an antibiotic is added to the plant cells, only those cells that have successfully integrated the GM gene cassette into their DNA will survive. If the antibiotic resistance marker gene is physically linked to the GM gene of interest, it remains in the final GM crop that is commercialized.

In an in vitro study (laboratory study not performed in living animals or humans), GM Bt maize DNA was found to survive processing and was detected in the digestive fluids of sheep. This raises the possibility that the antibiotic resistance gene in the maize could be incorporated into the DNA of gut bacteria, an example of horizontal gene transfer.67 If the antibiotic resistance gene transferred to a pathogenic bacterial species, this could result in antibiotic-resistant disease-causing bacteria (“superbugs”) in the gut.

What tests should GM crop developers do to ensure that they are safe to eat?

The following tests are the minimum that should be carried out in order to ensure that a GM food is safe to eat.

1. A full range of “omics” molecular profiling analyses should be carried out (genomics, transcriptomics, proteomics, and metabolomics). Profiling of siRNA (gene-silencing RNA) and microRNA (miRNA) molecules should be conducted, to look for intended and unintended changes brought about by the genetic engineering process. Unlike regular RNA molecules, which code for proteins, miRNA molecules regulate gene expression.

These “omics” profiling tests must be done on the GMO and the isogenic non-GMO grown at same location and time, in order to highlight the presence of potential toxins, allergens, and compositional/nutritional disturbances caused by the GM transformation. There must be no spurious use of non-isogenic controls, as is often done by industry in tests conducted for regulatory purposes.

2. Long-term feeding studies should be carried out in an appropriate laboratory animal species. The studies should include:

  • Comparison of the GMO with isogenic non-GMO only.
  • At least three doses of the GMO and any relevant agrochemicals, including a physiologically relevant dose to which a population could be exposed.
  • Three parallel arms of investigation addressing toxicity, carcinogenicity, and multigenerational effects.
  • Toxicokinetics analysis of the pesticide, to find out what happens to it once it enters the body of an animal or human that consumes it. This includes how and where it travels in the body, how it breaks down and into what, how efficiently it is excreted, and to what extent and where it bioaccumulates. The entire pesticide formulation as sold and used must be tested; and in the case of pesticide-producing GM plants, the pesticide isolated from the GM plant must be tested as well as the entire GM plant.
  • Comprehensive anatomical, histological (microscopic examination of body tissues), physiological, and biochemical analysis of organs, blood, and urine.
  • Molecular profiling of selected organs from test animals to evaluate effects on gene expression, proteins, metabolites, and RNA interference, which could underlie any negative health effects observed.

If a herbicide-tolerant GM crop is being tested, then the herbicide must be tested both alone and in combination with the GM crop (sprayed on during cultivation according to normal practice). The full commercial formulations of herbicides should be tested, as they are sold and used. This study design enables the effects of the GMO to be distinguished from the effects of the herbicide and enables the researchers to determine if the GMO, the herbicide, or a combination of the two are at the basis of any negative health effects observed.

If a pesticide-expressing crop is being tested (e.g. a Bt crop), the pesticide product (e.g. Bt toxin) isolated from the GM crop must be toxicologically tested, as well as testing the whole Bt crop given in feed. It is not adequate to test Bt toxin protein produced from bacteria, which is the current practice of industry in its applications for regulatory authorization. Bt toxin produced from bacteria is only equivalent to the Bt toxin produced in the GM crop in terms of the amino acid sequence. It is not equivalent in terms of the post-translational modifications – the chemical modifications that occur to the protein in the new host organism as an indirect result of the GM gene transfer. Any post-translational modifications to the Bt toxin in bacteria will be markedly different from those in the plant or even completely absent. This is because bacteria lack the ability to perform the post-translational modifications that higher organisms like plants are capable of.

If the Bt toxin is tested only by feeding the whole GM plant and toxicity is found, it is not possible to know if the cause is the Bt toxin, or some novel toxin produced in the plant as a result of the mutagenic effects of the GM process, or the two combined. Hence there is a need to test the Bt toxin isolated from the GM plant as well as the whole Bt crop in order to understand the source of any toxicity.

It is also possible to test the same Bt toxin produced from GM bacteria, in addition. This enables the researchers to determine if any toxicity is due to the post-translational modifications brought about specifically in the GM plant as a result of the genetic engineering process.

3. Following on from the animal feeding studies, the following should be carried out:

  • Farm animal toxicity study along the same lines as the laboratory animal feeding studies.
  • Long-term dose escalation trials in human volunteers.


Contrary to frequent claims that there is no evidence of dangers to health from GM foods and crops, peer-reviewed studies have found potential signs of toxicity and actual harmful effects on the health of laboratory and farm animals fed GMOs. These include toxic and allergenic effects.

Most animal feeding studies on GMOs have only been short-term or medium-term in length. While GM proponents claim that the observed harmful effects on health are not “biologically relevant” or “adverse”, such claims are scientifically unjustifiable, as these terms have not been properly defined with respect to GMOs.

What is needed are long-term and multi-generational studies on GMOs to see if the changes found in short- and medium-term studies, which are suggestive of harmful health effects, develop into serious disease, premature death, or reproductive or developmental effects. Such studies are not required by regulators anywhere in the world.


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