Genetically modified organisms (GMOs) or genetically engineered (GE) foods have the potential to cause a variety of health problems.  For example, they may produce new allergens and toxins, and spread harmful traits to non-GMO crops. In addition, at least one major environmental impact of genetic engineering has already reached critical proportions: overuse of herbicide-tolerant GE crops has spurred an increase in herbicide use and an epidemic of herbicide-resistant "superweeds," which will lead to even more herbicide use. The long-term impacts of GMOs are unknown, and once released into the environment they cannot be recalled.

Even the loss of milkweed that Monarch butterflies depend on, (and other sources of nectar and pollen that wild pollinators require to survive) is an environmental side effect of intensive herbicide use associated with GE crops.

Suppressing Science

Sadly, the ability to test GMOs independently is severely limited. According to Scientific American, several large agri-technology companies explicitly forbid the use of their seeds in independent research.  Instead, the companies pick the favorable studies to highlight, and do not promote those which are unfavorable to their work to “ever see the light of a peer-reviewed journal”.

So what evidence is available?

When scientists have been able to study these crops, the results have been disturbing.  A study published last November in the Journal of Food and Chemical Toxicology found that GMO maize provoked chronic hormone and sex dependent pathologies in rats.  Female rat mortality was 2 to 3 times higher mostly due to large mammary tumors and disabled pituitary gland function, and males had liver congestion, necrosis, severe kidney nephropathies and large palpable tumors.

Why the concern over Bt in Corn?  Isn’t it used in organic farming?

The Bt toxin expressed in GM plants is structurally very different from natural Bt used as a spray. The Bt toxin in GM plants is not always fully broken down in digestion and has been found to have toxic effects on laboratory animals and non-target organisms fed on such crops.

Herbicide Link

GMO crops are often grown with large amounts of herbicide that have potentially toxic effects.  Research has found that an “inert” ingredient in an herbicide usually paired with GMO crops can kill human embryonic, placental, and umbilical cord cells.  In one study, scientists found that inert ingredients in the herbicide amplified the toxic effect on human cells—even at concentrations much more diluted than those used on farms and lawns.  One specific inert ingredient, POEA, was more deadly to human embryonic, placental and umbilical cord cells than the herbicide itself – a finding the researchers called “astonishing.”   Cell damage occurred even at the residual levels found on herbicide-treated crops, lawns and gardens. This popular herbicide is thought to possibly cause pregnancy problems by interfering with hormone production, possibly leading to abnormal fetal development, low birth weights or miscarriages.


Allergens are a potential issue, for example the proposed genetically engineered salmon contains eel DNA, and the changes in the salmon DNA may have further enhanced the allergenicity of the modified salmon.

In addition, the EU has acknowledged the potential for allergic reactions in some persons in GE crops.

Putting the Science in perspective

Michael Hansen, Ph.D., Senior Scientist at Consumers Union, has outlined specific concerns in his testimony to state legislatures, including Washington State and Connecticut.   He posits that genetic modification is not an exact science - genes are not always inserted into the DNA exactly where they were intended. The effects of this are not well understood, and the risks of new allergens and novel toxicities cannot be discounted.

The United States, however, unlike all other developed countries, does not require safety testing for GE plants (although it does require an assessment for GE animals). The US Food and Drug Administration’s (FDA) original policy on GE plants, developed more than twenty years ago, says that companies may go through a “voluntary safety consultation.” But, in the end, FDA says it is up to the companies to determine safety of any GE food.

In Summary

Genetic engineering is a new technology. The claim that humans have been genetically engineering plants and animals for thousands of years misrepresents the facts. With genetic engineering you can move cow genes into pigs, flounder gene into tomato, scorpion gene into corn, mouse gene into pigs, spider gene into goats, human genes into rice, barley, and safflower, and jellyfish genes into rabbits and dogs. All these examples of new life forms that have been created using GE could never be created using conventional breeding or even new techniques like irradiation breeding or mutation breeding. GE has also been used to move genes for resistance to the antibiotics kanamycin, streptomycin and amoxicillin into plants; again a feat that cannot be accomplished by conventional, mutation or irradiation breeding.

GM proponents have long promised climate-ready and drought-tolerant crops, but conventional breeding has been far more successful than GM technology in producing such crops. This is unsurprising, as these traits are genetically complex and cannot be produced by manipulating one or two genes.  It is not necessary to accept the risks posed by GM crops when conventional breeding – sometimes assisted by safe biotechnologies such as marker assisted selection – continues to successfully produce crops that are high-yielding, drought-tolerant, climate-ready, pest- and disease-resistant, and nutritious. Conventional breeding, the existing crop varieties developed by farmers worldwide, and agroecological farming methods, are proven effective methods of meeting our current and future food needs.


Monsanto supported GMO labeling in Europe, but not in the U.S.

Whistleblower scientists

British scientist Arpad Pusztai was one of the first to whistleblow that there could be problems with GE foods.  In 1998, he released to the media results that he said indicated that rats fed potatoes genetically engineered to

contain a lectin from the snowdrop plant--a naturally occurring insecticide--had suffered damaged immune systems and stunted growth of vital organs. The results stood in stark contrast to safety claims made by

biotech companies and to the received wisdom of the harmlessness of transgenic crops.


Highlights from Dr. Michael Hansen’s testimony to Washington state legislature

See the complete testimony at

The inadequacy of FDA’s policy can be seen in the letter FDA sends to the company after completion of a “safety consultation.” For example, the letter sent to Monsanto on September 25, 1996 about one of their first Bt-corn varieties, MON810, states, “Based on the safety and nutritional assessment you have conducted, it is our understanding that Monsanto has concluded that corn grain and forage derived from the new variety are not materially different in composition, safety, or other relevant parameters from corn grain and forage currently on the market, and that they do not raise issues that would require premarket review or approval by FDA” (bold added by Dr. Hansen).  

The letters for all 94 “safety consultations” done since the first, for the Flavr Savr tomato, contain basically the same language. This clearly shows that the FDA has not made a conclusion about the safety for genetically engineered (GE) plants or the safety of the technology as a whole.

To assess the health impacts of GE foods, it is essential to label GE plants and animals so as to be able to track any potential adverse human health or nutritional impacts. It will be very difficult for FDA or a doctor to identify the source of any unforeseen problem if they have no idea what foods a person is eating. For example, suppose a company decides to insert a synthetic gene, which codes for a modified protein, into corn and decides not to notify the FDA for currently acceptable reasons (i.e. the company thinks that the modification was “minor”). Suppose that the novel protein causes a strong but delayed (say by 24 hours) allergic reaction (e.g. serious rash, upset stomach, or anaphylactic shock) in some relatively small subset of the population. To start with, doctors would have an extremely difficult time identifying the source of the problem.  

If the offending GE corn variety is not very prevalent (i.e. does not have a large market share), then the regular allergy test, making a list of all foods eaten in the last 24 hours, might not uncover the GE corn as the source of the problem (the person would have to obtain and eat the offending GE corn variety a second time and get the same reaction). It might well take large numbers of people being adversely affected and having the offending GE corn variety be a large share of the market before there would be any hope of figuring out that a problem even existed.

One big problem with safety assessments of GE plants is that there have been virtually no long-term animal feeding studies, with most feeding studies being of 90 days or shorter. A carefully designed meta-analysis was done of 19 published studies involving mammals fed GE corn or soy. The meta-analysis also included the raw data from all the published studies that could be found as well as a number of 90-daylong feeding studies that were obtained as a result of court action or official requests. The meta-analysis highlighted damage in the kidney, liver and bone marrow, which could be potential indicators for the onset of chronic diseases.10 However, no animal tests are obligatory for any of the GMOs cultivated on a large scale in the US.  

Last fall, a study was published that was the first long-term (e.g. 2 years) feeding study which involved rats fed Roundup-resistant corn (NK 603).  The study found that females rats fed the GE corn died 2-3 times more quickly, and developed mammary tumors more often than controls who ate non-GE corn, while male rats fed the GE corn have liver and kidney problems at higher rate than controls, and more large tumors than rats fed non-GE corn. This study, by Dr. Giles-Eric Séralini received a lot of media attention. The study was viciously attacked in the media by pro-GE and industry-affiliated scientists in what appears to have been an orchestrated campaign.  The two main criticisms were that they used too few rat per group and that they used a strain of rat (Sprague Dawley) that is prone to mammary tumors as they age. Both criticisms are off base. The Séralini et al. study took measurements on 10 rats per group, the same number of rats that Monsanto took measurements on in their 90 day feeding study, which was published in the same journal eight years before the Séralini study. If ten rats is too small a sample size to demonstrate health problems, how come ten rats is a sufficient sample size to demonstrate no safety concerns? As for the strain of rat use, Séralini used the same strain (Sprague Dawley) that was used in the Monsanto feeding study. In addition, the same strarat was used in a Monsanto-sponsored two-year feeding study of rats fed glyphosate as part ofreregistration process in Europe. Why is use of SD rats bad when Séralini uses them, but ok when Monsanto and other biotech companies use them.

Both the French Food Safety Agency (ANSES) and the European Food Safety Authority (EFSA) have concluded that such long-term safety assessment should be done on GE foods. Indeed, the ANSES report on the Séralini study notes, “ANSES recommends initiating studies and research on the long-term effects of GMOs in combination with plant protection products … [and] calls for public funding on the national and European level to enable large-scale studies and research for consolidating knowledge of insufficiently documented health risks.” At a meeting in December, the “EFSA board meeting on Thursday last week there was agreement that long-term studies were needed and it was now just a question of how to fund them.”  If the Séralini study is so flawed, why have ANSES and EFSA functionally agreed with its call for independently-funded long-term feeding studies on GE crops?  

In addition to FDA not requiring any premarket safety testing, there is virtually no independent safety testing of these crops in the US due to intellectual property right problems. When farmers buy GE seed in the US, they invariably must sign a product stewardship agreement which forbids them from giving such seeds to researchers.15 In addition, researchers must get permission from the biotech companies before they can do research, the result is a paucity of independent research. Scientists have even been threatened with legal action if they revealed information obtained via freedom-of-information.16 In early 2009 26 public sector scientists in the US took the unprecedented step of writing to the US Environmental Protection Agency (EPA) protesting that “as a result of restricted access, no truly independent research can be legally conducted on many critical questions regarding the technology.” As a result, the editors of Scientific American published a perspective stating that “we also believe food safety and environmental protection depend on making plant products available to regular scientific scrutiny. Agricultural technology companies should therefore immediately remove the restriction on research from their end-user agreements.” We concur and believe that only truly independent safety tests will give us an answer about the safety of GE foods. In the meantime, it’s crucial that GE foods be labeled, so that if people experience negative effects, they and their doctors can identify them.

Finally, at least 62 countries, which together include more than half the world’s population, (including all European Union, China, India, Japan, Korea, Australia, Russia, Brazil and South Africa), require labeling of GE foods.18 A number of polls from 1995 to 2011 have found that between 70% and 95% of Americans polled supported mandatory labeling.19 A 2008 Consumers Union nationwide poll found that 95 percent of respondents said they thought food from genetically engineered animals should be labeled, and 78 percent strongly agreed with this.20 A ballot initiative last November in California (Prop 37) lost by just 51% to 49%, despite an advertising blitz in which industry outspent consumer and environmental groups by over five to one. Recent polling of those who voted no on Prop 37 showed that 20% actually favor GE labeling, but were convinced by the industry ads that this initiative was poorly worded or too weak. For all these reasons, CU strongly supports [GMO labeling]. 


References from Dr. Hansen’s testimony


 1 Consumers Union is the public policy and advocacy division of Consumer Reports. Consumers Union works for telecommunications reform, health reform, food and product safety, financial reform, and other consumer issues. Consumer Reports, a non-profit, is the world’s largest independent product-testing organization. Using its more than 50 labs, auto test center, and survey research center, the nonprofit rates thousands of products and services annually. Founded in 1936, Consumer Reports has over 8 million subscribers to its magazine, website, and other publications. 


2 At:


3 Pg. 22991 in FDA. Statement of Policy: Foods Derived From New Plant Varieties, May 29, 1992, Federal Register vol. 57, No. 104. At:


4 At:




6 Hansen, M. 2010. Submission to FDA’s Veterinary Medicine Advisory Committee meeting on safety assessment of AquAdvantage Salmon.


7 LeVaux, A. 2013. A risk scientist comments on AquAdvantage Salmon. February 13, 2013. At:


8 See Hansen, 2010. Op cit.


9 Séralini, G-E, Mesnage, R., Clair, E., Gress, S., de Vendômois, JS and D. Cellier. 2011. Genetically modified crops safety assessments: present limits and possible improvements. Environmental Sciences Europe, 23: 10. At:


10 Pg. 1 in IBID.


11 Séralini et al. 2012. Long term toxicity of a Roundup herbicide and a Roundup-tolerant genetically modified maize. Food and Chemical Toxicology, 50: 4221-4231.


12 Bardocz S, Clark A, Ewen S, Hansen, M, Heinemann J, Latham J, Pusztai A, Schubert D and A Wilson. 2012. Séralini and science: An open letter. Independent Science News. At:


13 Reaction of ANSES (French Agency for food, environmental and occupational health and safety) to Séralini et al. study


14 Commission and EFSA agree need for two-year GMO feeding studies. EU Food Policy, 17 December 2012


15 Waltz, E. 2009. Under wraps. Nature Biotechnology, 27(10): 880-882. At:






18 See




20 At: