Ask Us Anything About GMOs!

You say there are many studies that conclude GMOs are safe, but how many of those studies have spanned a timeframe 10 years or longer? It can take 10 years or longer for side effects such as cancer to show up in the human body. If there few or no studies that have spanned 10 years or longer, then how can you truly conclude that GMOs are safe? GMO safety is quite an "assumption" to make if you have no long term studies to back up your claims.

A:Expert Answer

Bruce Chassy, Professor Emeritus of Food Safety and Nutritional Sciences, Department of Food Science and Human Nutrition, University of Illinois at Urbana-Champaign, explores the topic of long-term studies in several recent responses. A few excerpts are included below.


“It’s important to recognize that there is an unstated assumption underlying this question. The question assumes that transgenics are inherently different in some way that might prompt us to wonder about their long term effects.  Are GM crops really different?  Obviously the answer to that depends on how one defines a difference.  Almost none of our crops grown today exist as such in nature; very few even resemble the wild ancestral plants from which they were domesticated.  Virtually all our crop plants have been genetically modified by a combination of human selection of desirable phenotypes from spontaneous changes and/or human induced mutations in DNA, without a detailed understanding of the genomic or compositional changes. Changes in DNA, or genetic modifications underlie all crop plant improvements. The methods of modern molecular biology that are used in the laboratory to breed transgenic plants are simply new and more precise tools that allow researchers to introduce new traits into plants. There is a substantial body of evidence that shows that transgenic breeding used to develop new GM crop varieties actually causes fewer unwanted changes in the DNA, in gene expression (transcriptome), in the proteins present in the crop plant (proteome), and in the composition of the plant (metabolome).


Said another way, transgenic plants are in every measureable way more like the plants from which they were developed than are other varieties of the same crop developed via breeding methods that were considered conventional. Research shows that transgene insertion is more precise and less disruptive to the cell’s genetic make-up than other methods used in the plant-breeding laboratory such as chemical and radiation mutagenesis.  A new GM variety often contains a single well-characterized gene that has added to 30,000 or 40,000 plant genes while traditional varieties may contain hundreds of uncharacterized mutations and/or unknown foreign genes. And the product of that gene was considered safe. The National Academy of Sciences of the USA and many other countries, every credible scientific society, global regulatory bodies and expert panels from around the globe that have studied the issues have all concluded that GM crops are less likely to have suffered from unintended changes in breeding that might produce undesirable effects than are crops produced by traditional methods of breeding.  So to return to the implicit assertion that GM crops are in some way different, the best science says that they are not meaningfully different than others from a hazard or risk perspective.  Although it can be argued they are, if anything, less likely to contain unwanted surprises. Since comparisons are made to foods that have a history of safe use, it should also be noted here that plant breeding has proven to be a very safe process over many years.


There are technical reasons why foods prepared from individual specific varieties of crops don’t produce adverse effects over 40-50 years.  Any food is a complex mixture of 1000s of compounds, which are safe for consumption in the amounts present in that food (and in our total diet).  It’s important to recognize that every chemical including essential vitamins and other nutrients can be toxic if we consume too much of them.  Long-term toxicity from foods is seldom observed.   That's because most of the food is digested, absorbed, metabolized and excreted; the unabsorbed portion passes through our bodies unchanged and is eliminated.  Unlike some chemicals, food components generally don't bio-accumulate so no adverse effects could be seen in 40-50 years.  There are a few exceptions to this rule.  For example consumption of shark or polar bear liver over a long period of time can cause hypervitaminosis D which can be lethal.  Lathyrism is a neurological disease that results from eating certain legumes such as  Lathyrus sativus (Grass pea) which contain a highly toxic compound, Oxalyldiaminopropionic acid (ODAP).  OADP is a structural analog of glutamate, an important neural transmitter. The composition of biotech foods is carefully studied to ensure that all components are within the ranges of concentration normally observed in that food; special attention is focused on the concentration of constituents such as Vitamin D or other anti-nutrients that could cause adverse effects if consumed in large amounts.  And, since crop composition data show that GM crops are less altered in their composition than crops produced by more disruptive black-box conventional breeding methods, the odds of an adverse effect arising in 50 years from the consumption of a new GM variety as part of our overall diet are less than they would be from the consumption of other varieties of the same crop—but remember, crop plant breeding has proven to be a very safe process.  We are talking about food here, not toxic waste.”


This response is available here:


A passage from another response provided by Dr. Chassy reads:


“The composition of GM crops and foods derived from them is carefully studied.  Using our knowledge of toxicology, food allergy, and nutrition, it is possible to predict if a food will have an adverse effect based on composition alone.  The study of composition is a better indicator of safety than are animal studies on whole foods.  Many scientists in fact question if whole food studies in animals are useful and have suggested they not been done.  Studies in humans are even more difficult to do and would likely yield little useful information since the diets' composition is the same, the outcome would be the same.  Since these are whole foods, with animal studies animals can be fed diets containing large amounts of the food ingredient being tested every day, which would be very difficult to do with humans.  Moreover, at the end of a study with animals, post-mortem examinations are performed that allow for a careful pathological examination of most all tissues to understand the pathologies that resulted from consuming large amounts of the whole food tested.


It's a general scientific principle that to do a good animal or human study a clear hypothesis and a means to test it are required.  Whole food feeding studies lack an hypothesis.  The underlying problem with whole food studies is that foods are complex mixtures of thousands of compounds rather than single pure chemicals.  Toxicologists use animal studies with single chemicals to test their toxicity (remember that virtually every chemical including nutrients required in the human diet can be toxic if we ingest too much). Foods are of course generally safe to eat so new varieties of crops are not tested in animals or humans.  There is a significant scientific consensus, based on quite a few composition studies, that demonstrates that GM crops composition is more similar to the parental strain from which they were bred than are other varieties of the same crop.  So, if we were going to ask for human or animal studies on whole foods, we should be asking for the on crops bred by non-GM methods.”


This response is available here:


A response from  Peter Davies, Professor of Plant Physiology and International Professor of Plant Biology, Cornell University, Ithaca New York, also addresses this topic:


“GM crops are not expected to present any new food risk, as the changes are simply in a molecules (protein and DNA) that have been in our diet for ever, and the small quantity of added material is degraded in our gut in exactly the same way as has always occurred. There has been very extensive safety testing carried out in many countries around the world, and GM-crops have been found to be no different from non GM-crops of the same species in terms of safety as food, or in environmental effects.


The European Union has said: “The main conclusion to be drawn from the efforts of more than 130 research projects, covering a period of more than 25 years of research and involving more than 500 independent research groups, is that biotechnology, and in particular GMOs, are not per se more risky than conventional plant breeding technologies” ("A decade of EU-funded GMO research," Directorate-General for Research and Innovation, European Union, 2010).”


The full response is available here:


Additionally David Tribe, senior lecturer in the Department of Microbiology and Immunology at the University of Melbourne, recently posted an infographic which lists a number of the scientific organizations and their specific statements on GMOs, available here.


If you have additional questions after reviewing these responses, please ask.

Topic: Safety, Health, and Nutrition  3 Comments | Add Comment