By David Schubert

from GeneWatch 29-1 | Jan-May 2016

Most people would prefer to have foods containing genetically modified products labeled as such. The simple right of people to know what they are eating is certainly valid, but the major reason for having this information should be personal health. In the rhetoric surrounding the benefits and hazards of genetically modified (GM) foods, anyone who claims that the technology is proven to be safe should be immediately dismissed as either naïve or dishonest for a few very simple reasons: (1) All existing plants produced by GM technology are different from each other and all pose different levels of risk to health; (2) Because most anything is possible in the world of genetic engineering, we have no way of knowing what will be introduced into our food chain in the future, and; (3) Finally, this is all made more problematic because there is no required Food and Drug Administration (FDA) safety testing of any GM product, and in fact to date none has been tested for toxicity.[1][2] Therefore, in the context of GM foods, the American food system essentially offers a carte blanche for the producers if they can sell their product, and they assume that it will be easier to sell without a GMO label. Clearly, this is not in the best interest of the consumer.

An example of point 1 is a simple comparison between three existing crops (herbicide resistant soybeans, Bt-expressing corn, and GM papaya). The production of GM soy requires large amounts of herbicides containing the chemical glyphosate, declared a probable carcinogen by the World Health Organization (WHO).[3][4] Glyphosate, along with the many unknown and likely toxic chemicals in the herbicide spray formulation that uses glyphosate, are found in high enough concentrations to be a health hazard in the beans. In contrast, Bt-corn makes a bacterial insecticide that binds to and damages cells of the gut of insects and likely does the same in humans.[5] Finally, the GM papaya was engineered to resist a plant virus and may be perfectly safe to eat.[6] But until some comprehensive safety testing protocols are mandated, at a minimum similar to those required for all other food additives, the buyer should be given the option of whether to take the risk or not.

Second, new GM food products are being commercialized rapidly, and from my view as a medical research scientist, some of these may lead to the biggest GM food-related public health disaster of all. Rather than have the plants make an enzyme for herbicide resistance, a bacterial toxin, or an antiviral protein, the next generation will include nutritionally enhanced plants (NEPs) that are engineered to make molecules that are biologically active in humans. Examples are plants that overproduce certain fatty acids or vitamins. The insertion of genes leading to new synthetic pathways can lead to the production of toxic by-products. Golden rice and yellow bananas are engineered to produce large amounts of beta-carotene, the precursor to vitamin A. In both, the likelihood of accidentally producing retinoic acid or related compounds, that are toxic at extremely low doses, is very high.[7] In fact, such a product was associated with the death of dozens of people when bacteria were engineered to produce higher levels of a tryptophan dietary supplement.[8] This case would have been much harder to trace to the source without the required labeling of the supplement. A label stating that the bright yellow banana is made by GM would serve as a warning if the buyer had concerns about the lack of safety testing for this novel food. Pregnant women should be particularly concerned, because retinoids cause birth defects.

Finally, presented with the fact that there is no required safety testing for any of these novel food products, most people simply do not believe that the FDA, mandated to protect our food supply, could be so uninterested. The reason is very simple. The laws that dictate the approval of GM foods were written by Monsanto, the company that developed the first GM plants.[9] Despite the objections of many FDA scientists at the time, it was ruled that GM plants were substantially equivalent to their safe relatives in the food supply at the time and, therefore, generally recognized as safe. This is clearly an incorrect conclusion since each and every GM plant is distinct from the conventional cultivar from which it was derived. Nonetheless, the assumption of "substantial equivalence" remains the law of the land and is exploited daily by industry.

In addition to the generic arguments outlined above for GM food labeling, it is important to discuss a few invalid claims continuously made by the commercial and academic interests that oppose GM food labeling. In order to debunk these statements, each will be discussed briefly with references to more thoroughly documented material.

"There is a scientific consensus that GM foods are safe." Many other scientists and I can assure you that this claim is logically flawed because there is absolutely no evidence for human safety, all GMOs are different, and we do not know about future GMOs. Most importantly, there is increasing evidence within the scientific and medical communities that GM food crops and the agricultural chemicals required for their production are potentially dangerous.[10][11] Within the U.S., the scientific discussion of health hazards associated with GM crops is muted because it is largely controlled by industry and pro-industry plant scientists within the major scientific organizations such as the American Association for the Advancement of Science (AAAS), and company-sponsored bureaucrats and scientists within the government regulatory agencies such as the FDA and the Environmental Protection Agency (EPA).[12][13] Academic scientists are frequently financially involved with companies in the GM crop pipeline whose products ultimately must be sold to the big seed companies like Monsanto and Dow for commercial development. These scientists clearly have a vested interest in claiming universal safety and preventing labeling. In sharp contrast, a significant part of the world scientific community expresses concern about the rapid and largely uncontrolled introduction of GM foods and their associated pesticides, and supports labeling. These scientists are routinely attacked and vilified by the GM producers, and because of this other scientists are either intimidated or extorted to prevent them from expressing their concerns.[14][15] The agricultural chemical and seed industries do not have the same political power in most countries as they do in the US; therefore GM food labeling is required in the majority of countries around the world. There is, in fact, no scientific consensus that GM foods are safe.[16]

"GM is just like traditional breeding, but more precise." The production of GM crops has absolutely no relationship to standard plant breeding.[17] The statement about precision is not true with the current GM crops, where gene insertion has been random. It is also not a reflection of reality in terms of the consequences of using newer technologies where genes can be inserted into the genome more accurately. This is because being more precise does not mean there is a greater ability to either understand or predict the outcome. You can precisely cut and rearrange a Chinese text without a clue about meaning unless you understand the language. At this point we clearly do not understand the details of how genes are regulated, and one currently cannot predict all of the downstream consequences of any genetic manipulation, regardless of how precisely it was done. In contrast, traditional breeding moves large blocks of genes around where the loss of regulatory controls is less likely to occur. Therefore, GM foods are very different from traditional crops and should be labeled as such.

"There is no evidence that GM crops are harmful." There are three aspects to this statement that at this time are difficult to separate. First, because there is no safety testing, no epidemiology and no clinical trials, no one can say that GM crops are safe to eat. The second involves the GM crop itself, and the third the agricultural chemicals required for their production. The toxicity of the chemicals is unambiguous, while the direct toxicity of the plants themselves is less well studied and varies with the modification.

GM soy and corn make up the vast majority of GM crops and most of these are engineered to be resistant to herbicides containing glyphosate such as Roundup. Glyphosate from the herbicide spray gets into the cells of all plants and remains there for extended periods of time. But the glyphosate resistant GM crops do not die, while the surrounding weeds are killed. There are a number of studies showing that glyphosate is an endocrine disrupter and toxic to humans.[18][19] For these reasons, the WHO declared that it is a probable carcinogen. Since the introduction of GM plants, herbicide use has increased twenty-fold or more, and now there are very high levels in most soy and many corn products. Glyphosate is now found in extensive ecosystems, drinking water and in humans. However, perhaps the highest human exposure to glyphosate is from non-GM grains. Most grain crops (wheat, oats, barley) are sprayed with herbicide directly before harvest to speed up their death and make them dry faster. Because the chemicals must be inside the plants in order to kill them, they are inside the grains, and we eat and drink them. In the case of beer, frequently produced with crops that are "dried" with a herbicide, the concentration of glyphosate has been documented to be over 300 times the European limit allowed in drinking water.[20] Therefore, a product can be labeled non-GMO yet contain very high levels of toxic agricultural chemicals.

Food, water, and beverages should be tested for qlyphosate by the FDA or EPA. However, this is not done, probably for the same reason that there is no GM food safety testing required by the FDA. The only way to reduce exposure is to buy organic products, and these may not be herbicide-free if they are farmed with manure from GM-fed animals, a practice currently allowed under organic standards. Herbicides accumulate in this material and can be taken up by plants through their roots.

Unlike the chemicals used in their production, the direct toxicity of GM crops themselves is more difficult to study. Although there is no required safety testing, both industry in the U.S. and a few academic labs outside of the U.S. do carry out studies and make claims about safety. As may be expected, the industry sponsored studies claim that there are no health problems associated with GM soy and grain consumption, while many of the studies from academic labs continue to find serious toxicities that would typically stop the FDA allowance of any medicine or food additive. These issues are too complex to discuss here,[21] but it is quite clear that there are sufficient data to raise serious concerns about the safety of some of the current GM food crops, particularly those that are herbicide resistant and are likely to contain glyphosate and the other chemicals that are in the herbicide. An important caveat is that only a few of the many existing crops have been studied at all, so no claims about the global safety of the technology are valid.

In summary, there are no data to support the claim that GM products are universally safe. In contrast, there is increasing evidence from the scientific community that some GM crops and definitely the herbicides that are required to produce the major GM crops are toxic. To limit exposure, currently the best alternative is to require GM food labeling allowing people to avoid purchasing these products. The drying of grains with herbicides must be halted, and all food crops, beverages and drinking water should be monitored for herbicides, and indeed all chemical pesticides. Their allowance should be set to scientifically validated safe limits that are determined independently of the producer.

David Schubert, PhD, is a Professor and head of the Cellular Neurobiology Lab at the Salk Institute for Biological Studies.



1. Druker, S. (2015). Altered Genes, Twisted Truth: How the Venture to Genetically Engineer Our Food Has Subverted Science, Corrupted Government, and Systematically Deceived the Public, 1st edn (Salt Lake City, UT, 513 pp.: Clear River Press).

2. Freese, W., and Schubert, D. (2004). Safety testing of genetically engineered food. Biotechnology and Genetic Engineering Reviews 21:299-325.

3. Guyton, K.Z., Loomis, D., Grosse, Y., El Ghissassi, F., Benbrahim-Tallaa, L., Guha, N., Scoccianti, C., Mattock, H., Straif, K., and International Agency for Research on Cancer Monograph Working Group, I.L.F. (2015). Carcinogenicity of tetrachlorvinphos, parathion, malathion, diazinon, and glyphosate. Lancet Oncol 16:490-491.

4. Myers, J.P., Antoniou, M.N., Blumberg, B., Carroll, L., Colborn, T., Everett, L.G., Hansen, M., Landrigan, P.J., Lanphear, B.P., Mesnage, R., et al. (2016). Concerns over use of glyphosate-based herbicides and risks associated with exposures: a consensus statement. Environ Health 15:19.

5. Mesnage, R., Clair, E., Gress, S., Then, C., Szekacs, A., and Seralini, G.E. (2013). Cytotoxicity on human cells of Cry1Ab and Cry1Ac Bt insecticidal toxins alone or with a glyphosate-based herbicide. J Appl Toxicol 33:695-699.

6. Tripathi, S., Suzuki, J., and Gonsalves, D. (2007). Development of genetically engineered resistant papaya for papaya ringspot virus in a timely manner: a comprehensive and successful approach. Methods Mol Biol 354:197-240.

7. Schubert, 2008

8. Druker, 2015

9. Druker, 2015; Freese and Schubert, 2004

10. Druker, 2015; Myers et al., 2016

11. Landrigan, P.J., and Benbrook, C. (2015). GMOs, Herbicides, and Public Health. N Engl J Med 373:693-695.

12. Druker, 2015

13. Vallianatos, E.G., and Jenkins, M. (2015). Poison Spring: The Secret History of Pollution and the EPA, 1st edn (London, 304 pp: Bloomsbury Press).

14. Aviv, R. (February 10 2014). A valuable reputation. In The New Yorker: Annals of Science (New York, NY).

15. Johnson, R. (May 20 2014). Monsanto silences scientist who explores risks of gene modification. (

16. Krimsky, S. (2015). An illusory consensus behind GMO health assessment. Sci Technol Human Values (STHV) 40:883-914 doi: 810.1177/0162243915598381.

17. Druker, 2015

18. Summarized by Landrigan and Benbrook, 2015

19. Myers et al., 2016

20. Pesce, N.L. (NY Daily Times Thursday, February 25 2016). Popular German beers contain weed-killer linked dto cancer, study finds.

21. For details, see Druker, 2015 and:
Robinson, C., Antoniou, M.N., and Fagan, J. (2015). GMO Myths and truths: A citizen's guide to the evidence on the safety and efficacy of genetically modified crops and foods, 3rd edn (London, Great Britain, 164 pp: EarthOpenSource).

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