Opponents of GM crops often describe them as “untested” and “unsafe.” This is simply untrue. To better illustrate this, we have broken the very broad question of GM crop safety into a number of sections that, together, better address the testing and safety of GM crops.
Yes, food derived from authorized genetically-modified (GM) crops is as safe as conventional (non-GM-derived) food.
The first large acreage plantings of GM crops--herbicide tolerant soybeans and canola--took place in 1996 after successfully passing U.S. regulatory review. Since then, additional GM crops with herbicide tolerance, insect tolerance and virus resistance have been given clearance for planting and consumption. These include varieties of corn, sugar beets, squash and papaya. All of these crops have been assessed for food and feed safety in producing countries, and many more countries have approved the import of food or food ingredients that contain GM products. Hundreds of millions of meals containing food from GM crops have been consumed. There has not been a single substantiated instance of illness or harm associated with GM crops.
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Because existing food crops are recognized as safe, the logical starting point for safety assessment of a GM food is to ask “what’s different?”
Safety assessment can then be appropriately focused on what is different about the GM crop. All GM crops are analyzed and compared to non-GM counterparts in order to determine whether they have similar concentrations of proteins, carbohydrates, fats, amino acids, fiber, vitamins and a variety of other components. Two crops which are alike in all respects are said to be “substantially equivalent.”
All crops vary in nutrient and other components. No two crops--or even samples of the same crop--are identical. Substantial equivalence, more technically, means that the range of concentrations for components of the GM crop falls within the typical range for the non-GM counterpart.
Substantial equivalence is a useful concept which is accepted and utilized by most regulatory agencies worldwide, including the Canadian Food Inspection Agency, Japanese Ministry of Health and Welfare, the United Nations Food and Agricultural Organization, the World Health Organization, and the Organization for Economic Cooperation and Development. However, substantial equivalence is NOT the end of the assessment process--we still have to address anything that is new or different.
Existing, approved GM crops are substantially equivalent to conventional counterparts. The “what’s new” in these crops comes down to new DNA, which in turn produces a new protein (and new RNA encoding that protein).
So, how do we approach new DNA, RNA and proteins?
DNA (and resulting RNA) is present in almost all foods--the only exceptions being highly refined materials like oil or sugar from which all cell material has been removed. Thus, DNA is non-toxic and the presence of DNA, in and of itself, presents no hazard. 
When a new protein (not normally found in that plant or in other commonly consumed foods) is introduced into a plant, the safety of that protein does need to be addressed. It is standard practice to use animals to test any introduced proteins. Animal testing requires very high doses of the test substance be given. These levels are, by design, many times higher than those which people would actually consume. In GM crops and foods derived from them, introduced proteins are usually present only in minute amounts. Because the levels of protein are so low, it is impossible to test high doses by feeding crops directly to animals. Instead, a purified version of the introduced protein is used in animal studies.
In the near future, we will begin to see a new generation of GM crops which have improved nutritional value or other modifications to improve food or feed properties. For these new crops, there is still no need to assess the safety of DNA and RNA, and introduced proteins will still undergo safety assessment.
However, the answer to the “what’s different” question with these crops may include other, non-protein components such as improved fats and oils, improved vitamin content, or other exceptions to “substantial equivalence”. Appropriate safety assessment will need to be carried out for the other new components, but the details will necessarily vary from one to the next. One important consideration will be whether something is new to the human diet or just new to the particular crop. Materials not present in the diet may require extensive assessment. In contrast, a nutrient with a long history of safe use and limited toxicity (such as beta-carotene, a vitamin-A precursor) may require little additional assessment.
So long as the introduced protein is determined safe, food from GM crops determined to be substantially equivalent is not expected to pose any health risks. Further, it is impossible to design a long-term safety test in humans, which would require, for example, intake of large amounts of a particular GM product over a very large portion of the human life span. There is simply no practical way to learn anything via human studies of whole foods. This is why no existing food--conventional or GM--or food ingredient/additive has been subjected to this type of testing.
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Genetically modified plants generally contain only a limited number of new components (specific DNA, RNA, and proteins) not present in conventional varieties of the same crop. These components are defined specifically by the modification being made.
DNA (and the resulting RNA) are common to all biological systems and are known not to cause cancer. Proteins are also present in all biological systems, and proteins are not considered to be causes of cancer. Certain protein hormones or toxins may have the potential to influence cancer rates as a result of their specific biological activity. However, such biological activity is predictable from protein structure and will be easily recognized in acute toxicology studies. Proteins that could cause cancer are not used in GM plants.
Thus, there is no need to undertake lifetime animal cancer studies for GM foods that contain new DNA, RNA, and proteins with well-characterized functions. Conventional foods are not subjected to lifetime cancer testing. In the event that a GM food is modified to contain some other, chemically new component, the need for cancer testing would be addressed on an individual basis, depending on the nature of the material, knowledge from other exposures to the material in the diet and biological activity.
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There is no evidence to link allergenicity to currently authorized GM crops.
There is evidence to suggest that the reporting of allergies is increasing in some countries and geographic areas. This is likely due to several causes:
- There has been an increased interest in food allergies. Unfortunately, there are no stable diagnostic criteria for testing for food allergies and food intolerance. Together, these two factors have probably resulted in an increase in reporting of allergies. Therefore, rates of allergies may not have actually increased as much as it would appear.
- Increased prevalence of allergies is in some cases well documented. These are likely due to the fact that the consumption of some foods has increased in certain geographic areas. For instance, in the U.S., the use of soy-based infant formula has increased in the last 10-20 years. You need to be exposed to a substance in order to develop an allergy to it, and historically not as many people had been exposed to soy, particularly as infants, as they are today. Any increase in infant soy allergies is likely due to increased consumption of soy.
- There is also evidence that better household hygiene and reduced early exposure to allergens and infections may be partially responsible for increasing rates of some allergies. This has been called the “hygiene hypothesis”. Because exposure to certain allergens is removed or greatly reduced during infancy and early childhood, the immune systems may develop an improper or exaggerated response, which results in allergies later in life. Supporting evidence for this theory includes the fact that children on farms have lower rates of asthma than non-farm children, and children born into a household with a pet are also less likely to develop asthma than children in a home where a pet is introduced later in life.
Assessing the allergenicity of introduced proteins is a required component of the safety assessment of GM crops. There is no single test that can be used to determine if a substance is an allergen. Consequently allergenicity must be assessed on a case-by-case basis.
No matter what the source of the gene, every new protein is assessed for certain characteristics to help avoid the introduction of potential allergens into a GM crop. This is done by looking at two aspects of the protein:
- The physicochemical characteristics of the protein. We know that some allergenic proteins share certain physiochemical structures. Where the introduced protein in a GM crop shares such structures, they are subject to additional scrutiny as potential allergens.
- The susceptibility of the introduced protein to digestion. If a protein is quickly digested, it has less likelihood of being able to elicit an allergic reaction. This can be easily tested using enzymes important in protein digestion.
Sources of known allergens, such as nuts or eggs, are generally avoided as gene sources for GM crops. Where the source of a gene is known to contain an allergen, the GM crop is examined critically to determine whether the proteins that are introduced into the GM crop are the same proteins that are allergens in the source. This is done by comparing the protein to lists of known allergens, and by testing with the blood/serum of patients known to be allergic to the gene source.
There are hundreds of thousands of different proteins in the human diet, and only a tiny fraction of these are significant food allergens. Thus, the risk of a new protein being a food allergen is very low. By using a ‘weight of evidence’ approach which considers source, structure and digestibility, the risk of introducing an allergen into GM crops can be reduced to a negligible level.
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While there is evidence that girls are experiencing the onset of puberty at a younger age than they have in the past, there is no evidence to suggest that GM crops are involved. Most experts believe this is a result of improved nutrition.
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There are three basic bodies of evidence to support this statement:
- First, millions of tons of GM crops have been fed to farm animals for more than a decade. There is no evidence of early onset of puberty in farm animals.
- Second, studies with GM crops in laboratory animals also have failed to show any association between GM foods and early onset of puberty or other unexpected hormonal effects. (We have to say “unexpected, because all soybeans naturally contain phytoestrogens (http://www.merriam-webster.com/dictionary/phytoestrogen), which have known hormonal effects).
- Finally, the advancing age of puberty is a phenomenon that predates the introduction of GM crops, and which has occurred in most developed nations, despite the fact that GM use varies widely.
It is important to note that earlier onset of normal puberty is very different from precocious onset of abnormal puberty. With earlier onset of puberty, puberty is reached at an age that is earlier than historical norms, but is physiologically normal. There is no evidence to suggest that physiologically abnormal precocious puberty is on the rise.
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It’s common for the public to get conflicting information about scientific studies. This is not just an issue with biotech crops. You’ll often hear a report about something being good for you, and a month later there is another saying it’s bad for you. All of us, even scientists, experience some confusion with conflicting information, particularly when we do not work in a specific area of science.
When considering and comparing scientific data, you need to take several things into account:
1. Is the study designed and executed well and according to accepted methods?
2. Is it in alignment with other data on the same topic?
3. Do the results make scientific/biological sense?
4. Is the scope of the conclusions supported by the data?
For example, Bt crops have been modified to produce a protein that is toxic to various forms of insect larvae. Bt proteins have long been used as topical sprays in conventional and organic agriculture because they are effective and safe. Bt proteins are known to be practically non-toxic (the first rule of toxicology is that everything is toxic to some degree at sufficiently high doses) to humans and other mammals. The relative safety of Bt protein was one of the reasons it was chosen for use in many GM crops.
Several researchers have claimed to have done studies indicating that GM crops are unsafe. None fare well when you consider the points above. Take for example a study by Arpad Pusztai, where GM potato was fed to rats. The study results indicated that there was damage to the stomach lining of rats.
Pusztai created a GM potato expressing a protein toxin, known as the snowdrop lectin, derived from a toxic plant. Note that he did not use a commercially available GM crop. The GM potato used in this study had never been approved for consumption by any government agency. He compared this in a rat feeding study to conventional potato to which snowdrop lectin had been independently added. Pusztai claimed to observe injury to the stomachs in both the GM and non-GM potato, but he argued the GM potato was more toxic than the conventional potato plus added snowdrop lectin. Based on this study, Pusztai claims that GM foods in general are unsafe.
There are several problems with Pusztai’s work which resulted in his study being repudiated by the publishing journal, The Lancet.
- First, the number of rats per test group was far too small to document a difference in toxicity. Given the small number of test animals, the difference between the groups could have simply been a reflection of random variation.
- Second, the diet of the study rats was not equivalent between the test and control groups. Nutritional impacts, rather than toxicity, may have accounted for some of the harmful effects observed.
- Most importantly, Putzai did not determine whether the GM potato he developed was substantially equivalent to their non-GM potatoes. This would have been the first step in any regulatory review process. In fact, there is evidence that lectin is toxic to plant cells and can cause physiological changes to plant cells. It is extremely possible that the genetic changes he made to his test potatoes rendered them non-substantively equivalent.
There are a number of other examples, such as the work by Irena Ermakova, who claims that GM soybeans caused reproductive abnormalities in rats. This work was poorly designed and has been criticized by other scientists that have examined her study. It is noteworthy that this study received a lot of attention by groups critical of GM crops even though the study was never subjected to independent peer review and published in a reputable journal. One shortcoming mentioned by experts is that the test feed materials could not be fully characterized. This is important since unheated soybeans contain anti-nutrients that can have effects on test animals; and it is not clear how the test material was processed, nor is it possible to tell how much was consumed by particular animals due to an open cage design. More importantly, other well-performed and published studies conducted before and after Ermakova’s experiment do not substantiate her findings. Finally, it is difficult to reconcile her findings, since the introduced protein that makes GM soybeans tolerant to glyphosate in soybeans is common to many organisms and free of any known toxic effects. In short, Ermakova’s work is of questionable quality and is contradicted by many other high-quality, peer-reviewed studies that have been published in reputable scientific journals.
Lastly, there is a large body of documented scientific testing showing currently authorized GM crops are safe: Center for Environmental Risk Assessment. These studies focus on the wholesomeness and nutritional value of GM crops and upon the safety of the specific modifications used.
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