GMOs are short for genetically modified organisms because some aspect of the product's genome has been modified. To clarify, a crop/animal doesn't contain GMOs but rather it is the GMO. However, certain products may contain GMOs, such as yogurt, veggie burgers, granola bars, etc., if they contain ingredients that are genetically modified (like soy or corn) or if the animal was fed GMOs to produce the product (such as cows being fed GM corn to produce milk for yogurt or cheese).
GMOs have received a lot of negative attention from news outlets and social media. They have the connotation of being "bad" and "unhealthy", and people don't want to consume products with GMOs because they are "unnatural". Being an environmentalist, I am a proponent of organic agriculture, which excludes the use of GMOs; however, there are reasons why GMOs are controversial.
I wanted to dive into the pros and cons of GMOs, fully knowing the can of worms that is being opened. It is a difficult assessment: many organizations have an agenda, and it can be challenging to filter through both biased opinions and science. For every study that shows no negative effect of GMOs, you can find a study that does. The resulting need is to be able to critically examine the methodology and limitations of every paper to make a sound conclusion, and, well, I'm not going to do that here. I just want to emphasize that it's important to avoid fear-mongering news and pop articles and try to, instead, understand the science behind what is happening, including keeping an open mind while taking everything with a grain of salt.
Let's go.
Why are organisms modified?
Plants that are genetically modified (GM) typically occur in agriculture with the goal of increasing crop yields and/or having a product or animal with more desirable traits. With a constant reduction in farming area and arable land and an ever-growing (and hungry) human population, there needs to be a way to ensure that everyone gets fed (having access both in affordability and in physical access at markets). Many problems arise in agriculture that can threaten food security such as blights, pests, and weather events, like frosts and droughts.
The truth is, people have been modifying plants since 8000 BCE by selectively breeding crops based on desirable traits: kernels from the best corn (say, the sweeter, juicier, bigger kernels) were saved to plant again, while the subpar corn kernels were discarded. This is selectively choosing the best genes (though the concept of "genes" didn't exist until Gregor Mendel in the 1800s) and passing on those traits to future generations.
The first GMO crop arrived on the U.S. market in 1994: the Flavr Savr tomato. An enzyme in tomatoes made the tomatoes soften more quickly, decreasing shelf life, so researchers were able to genetically suppress this enzyme, allowing tomatoes to last longer [1]. With these engineered tomatoes outcompeting certain grocery store house brands, the stores advertised that their product was not genetically engineered, appealing to some customers. Some hazy messaging about the safety of GMOs based on a single mouse study [2] was broadcasted in 1998 that likely contributed to the decline in sales, but this information was supposedly later deemed incorrect by the researcher himself [1] .
Currently in the United States, the top modified crops are corn, soybean, and cotton. But how are crops modified?
Genetic Modification
Genes can be modified in a number of ways:
Slightly tweaking some DNA sequences in the crop, so the crop can display new traits
Inserting favorable genes (like heat, cold, and insect resistant genes) from one organism to another organism
Silencing “bad” genes, such as the genes that lead to apple browning
Why can GMOs be beneficial?
Herbicide Resistance
Crops can be modified to be herbicide resistant. For example, corn has been genetically altered to resist witchweed [3], a weed that reduces corn yields. By having a weed-resistant crop, less herbicide needs to be used which can be healthier for the applicator and the consumer.
Pesticide Resistance
Certain crops are resistant to pests which would otherwise eat and damage the crop. For example, rice has been bred to be resistant against the brown plant hopper [3]. Pesticide resistant crops can also lead to the usage of less pesticides.
Disease Resistance
Gene editing has allowed crops like cassavas, potatoes, maize, rice, and wheat to have favorable traits that combat diseases, like potato virus, banana streak virus, bacterial leaf blight, rice stripe virus, and maize lethal necrosis [3]. This is important to prevent widespread crop damage, such as the potato famine in Ireland in the 1800s when all the genetically identical potatoes were all wiped out from the same pathogen.
Environmental Hardiness
Droughts and frosts can impact the production of crops. Having crops that require less water for production can help save the copious amounts of water needed in agriculture, and plant traits can be modified to resist water shortages [4]. Also, crop genes can be edited to be more tolerant to cold temperatures [5], helping crops survive cold spells.
Improved Nutrition and Health
Millions of people globally are undernourished, and by bioengineering foods that are fortified in nutrients, low- and middle-income countries can benefit. Golden Rice is rice that has been genetically engineered to be fortified with Vitamin A in an effort to counter blindness (3 million+ preschool-aged children are inflicted by Vitamin A associated eye damage annually, and many die) [6]. Other foods biofortified with nutrients include corn, wheat, and crops to feed livestock. Certain protein in wheat that causes celiac-disease has been bioengineered out of the crop [6].
Rice has also been genetically altered to reduce arsenic and cadmium while cassava has been modified to be cyanide-free [3]. Genetically modified Bt corn also has lower levels of mycotoxins, toxic chemicals that are produced by fungi that take over the corn [7].
Also, did you know that life-saving insulin is a GM product? Here, bacteria are genetically modified instead of taking insulin from the pancreas of pigs.
Speediness
There's no doubt that it's faster. Instead of selectively choosing the best crops from each generation to use those seeds to make the future generations, creating a slow trend towards the ideal crop, genetically modifying crops is faster, supporting the demand of food to feed a growing population.
Why can GMOs be harmful?
Competition
Bioengineered organisms can be so successful in the environment, that they can outcompete native species. Such is the case with GM salmon: these salmon may grow and reproduce faster than the wild salmon, outcompeting them.
Weed/Pest Resistance
Also, by bioengineering crops to be pesticide and herbicide resistant, pests and weeds can become resistant as well [8]. Farmers have relied on a limited range of chemicals to kill weeds and pests, leading to resistance to that particular chemical. However, integrated pest and weed management (IPM and IWM) approaches should be used to preventatively combat resistant organisms, like applying multiple herbicides with different modes of action, rotating crops, planting weed-free seeds, scouting fields routinely, cleaning equipment to reduce the transmission of weeds to other fields, and maintaining field borders (more methods here).
Moreover, viral resistance can occur if GMO crops are created to be virus-resistant: the strongest viruses can overcome this obstacle, and fragments of the resistant viral DNA may incorporate into the DNA of other viruses, causing resistance and potentially new viruses [9]. Though this is a plausible consequence, it should be physically demonstrated.
Biodiversity
When a particular species is being killed (such as a particular pest or weed), the community of pests and weeds can change. Non-targeted pests may grow in numbers if not being targeted by chemicals, and this could also be problematic: this might cause a shift in damage to a plant population that was once unthreatened by pests, now being harmed by a new growing pest population. Non-targeted and beneficial insects could also be killed by chemicals intended for another pest [9].
Antibiotic Resistance
Some GMOs have antibiotic resistance markers (genes allowing cells that express a certain protein to be antibiotic resistant), and there is concern that these markers can cause pathogens to become resistant to antibiotics (such as gut bacteria). For this to work, someone or some animal would have to eat a GMO product with an antibiotic resistant marker, that marker would have to incorporate into the pathogen's DNA, and then it would have to survive long enough for transformation to occur. Antibiotic markers were found in the stomach and crop, but not intestine, of birds that were fed GMO maize, showing that the gene doesn't survive any longer than regular plant DNA [10]. Still, resistance is theoretically plausible through this mechanism, and more research should be done.
There is also concern that if someone is taking antibiotics while eating products that contain antibiotic resistant markers that the antibiotic could be rendered useless, but right now this is purely speculation.
Contamination/ Cross-Pollination
GMOs don't necessarily stay where they are supposed to: a GMO crop can accidentally mix with non-GMO crops during production and export, and this has lead to issues with countries closing borders to the U.S. for imports [11]. The reports of contamination are numerous. Also, genes from GMO crops can also cross into non-GMO crops, which is problematic for organic farmers who are not permitted to have GM crops in order to be labelled as "organic". Having an organic label is heavily time and labor intensive, so threatening the farmer's crop production can be physically and economically detrimental [12]. Also, if an herbicide-resistant gene were to escape and go into the nearby weed population, the weeds would become resistant, making it difficult to use herbicides.
Allergens
There are also arguments that GMOs can cause allergies when the gene of one organism is inserted into the genome of another organism. For instance, a gene from the Brazil nut was put into soybean, and the allergenicity of the Brazil nut was maintained in the soybean. Importantly, this product was never put on the market for human consumption. "This case helped establish the policy that any protein that has been shown or even suspected to cause an allergic reaction should never be introduced into a GMO crops. According to the international principles of food safety (FAO/WHO), before any GMO food gets market approval, the structure of the introduced protein should be compared to all known allergens," Charles Xu wrote in a Harvard article.
While diagnosed allergies have increased over the years, this correlation is not enough evidence of causation, though many people assume this. A systematic review found that GMO crops are not inherently more allergenic compared to non-GMO crops, but more research needs done to assess the physical development of allergy responses from GMO vs. non-GMO crops [13]. Alternatively, GM bean plants were found to induce allergies, but this product was quickly discarded; "Since the products of the transgenic are usually previously identified, the amount and effects of the product can be assessed before public consumption"[14] . Still, there is reasonable concern and enough warrant for more research.
Adverse Health Effects
A lot of people would say there are effects, and a lot of people would say there's not enough direct evidence. It would be beneficial to have more scientific studies to verify.
The issue: most scientific studies researching the effects of GM products on health have been done on animals, namely, mice and rats, and not on humans, so it's hard to say that the results of these studies can directly translate to human health. These studies also are pretty short, and multi-year studies should be done to see what happens to organisms after prolonged exposure. Also, the methods (endpoints, threshold of toxicity, quantity of exposure) vary by study, so it can be challenging to have a consensus. Science needs to be repeatable with the same outcome in order to be accepted as evidence, and, well, a lot of studies and conclusions haven't been repeated .
A number of studies have reviewed the safety of GMOs and have found varying evidence that GMOs cause harm. In a Harvard review, the authors discussed various studies which 1) found some evidence that GMO’s could cause harm in rodents, and 2) repeated the research that claimed negative side effects on a larger scale and found no evidence that GMOs caused harm to rodents, 3) found no evidence that GMOs caused harm to rat health and that DNA from ingested bioengineered food was not found in the DNA of the rats. In fact, the review also discussed studies that tracked the health of rats across three generations on a GMO diet, and none of the offspring showed negative results. However, other studies found that the liver and kidneys of rodents were impacted in the short term (28 or 90 days), but they said it doesn't indicate what could happen with long-term chronic toxicity [15,16]. Another study found that non-GMO and GMO diets didn't effect the reproduction of sows [17].
The studies showing both no effects and effects of GMOs are endless. Per Panchin and Tuzhikov:"the totality of the evidence should be taken into account when drawing conclusions on GMO safety, instead of far-fetched evidence from single studies with a high risk of bias due to a large number of multiple comparisons [18]". They mention that"it takes just a single article claiming a mild difference between GM and non-GM products to stir the public debate and cause a long-lasting hysteria." While they have a point, the fact that genes can move from one organism to another is enough concern for a lot of people, especially because the effects of those genes on humans are not well understood. While the gene itself might not be cause for concern, genes encode proteins, and the gene products may have harmful effects. As always, more research needs done.
Take Home Message
The fact that a product is “genetically modified” isn’t enough to conclude that it is unsafe; ongoing research needs to be done to know if GMOs are having any harmful effects on human health. However, there is no doubt that GMOs have benefits: by reducing the pests that destroy crops, yield is increased, and this decreases overall need for insecticides. Having a higher yield means increased food security, especially for low and middle income countries that need it most [3]. The reduction in pesticide and herbicide use means decreased greenhouse gas emissions due to not operating as much equipment. Having hardier crops that have a longer shelf life allows for reducing food waste, which in turn, conserves resources like water. Furthermore, GM crops can be fortified with nutrients to bolster health.
With the arguments for GMOs come the arguments against. Enough doubt has been introduced into the public for there to be suspicion regarding adverse health and environmental effects. Studies show harmful effects in animal models, but it's not clear what the effects on humans are. GMOs can also contaminate other crops, and they may outcompete native species.
Importantly, scientists are working to research the side effects of GMOs to address public health concerns, and protocols are in place to ensure (to the best of their ability) the safety of food products through testing and monitoring. If there was definitive proof that GMOs marketed for human consumption were linked to adverse health effects, then the product would be removed. Still, consumers have a right-to-know when it comes to decisions on what they are buying, and companies should be transparent by having labelling that specifies if products contain GMOs.
Regardless of the pros and cons of GMOs, supporting organic agriculture is important for a numbers of reasons, including it being overall better for the environment (future blog post?). By buying organic, you don't have to worry about the GMO controversy at all (well, except if GMOs contaminate organic farms), so support your local organic farm and organic farming research!
References
1. Bruening, G.; Lyons, J.M. The case of the FLAVR SAVR tomato. Calif. Agric. 2000, 54, 6–7.
2. Ewen, S.W.B.; Pusztai, A. Effect of diets containing genetically modified potatoes expressing Galanthus nivalis lectin on rat small intestine. Lancet 1999, 354, 1353–1354, doi:https://doi.org/10.1016/S0140-6736(98)05860-7.
3. Pixley, K. V; Falck-Zepeda, J.B.; Paarlberg, R.L.; Phillips, P.W.B.; Slamet-Loedin, I.H.; Dhugga, K.S.; Campos, H.; Gutterson, N. Genome-edited crops for improved food security of smallholder farmers. Nat. Genet. 2022, 54, 364–367, doi:10.1038/s41588-022-01046-7.
4. Luo, L.; Xia, H.; Lu, B.-R. Editorial: Crop Breeding for Drought Resistance. Front. Plant Sci. 2019, 10.
5. Yuwansiri, R.; Park, E.-J.; Jeknić, Z.; Chen, T.H.H. Enhancing Cold tolerance in Plants by Genetic Engineering of Glycinebetaine Synthesis BT - Plant Cold Hardiness: Gene Regulation and Genetic Engineering. In; Li, P.H., Palva, E.T., Eds.; Springer US: Boston, MA, 2002; pp. 259–275 ISBN 978-1-4615-0711-6.
6. Hefferon, K.L. Nutritionally enhanced food crops; progress and perspectives. Int. J. Mol. Sci. 2015, 16, 3895–3914, doi:10.3390/ijms16023895.
7. Wu, F. Mycotoxin reduction in Bt corn: potential economic, health, and regulatory impacts. Transgenic Res.2006, 15, 277–289, doi:10.1007/s11248-005-5237-1.
8. Anderson, J.A.; Ellsworth, P.C.; Faria, J.C.; Head, G.P.; Owen, M.D.K.; Pilcher, C.D.; Shelton, A.M.; Meissle, M. Genetically Engineered Crops: Importance of Diversified Integrated Pest Management for Agricultural Sustainability . Front. Bioeng. Biotechnol. 2019, 7.
9. Bawa AS, Anilakumar KR. Genetically modified foods: safety, risks and public concerns-a review. J Food Sci Technol. 2013 Dec;50(6):1035-46. doi: 10.1007/s13197-012-0899-1. Epub 2012 Dec 19. PMID: 24426015; PMCID: PMC3791249.
10. Philip A. Chambers, Paula S. Duggan, John Heritage, J. Michael Forbes, The fate of antibiotic resistance marker genes in transgenic plant feed material fed to chickens, Journal of Antimicrobial Chemotherapy, Volume 49, Issue 1, January 2002, Pages 161–164, https://doi.org/10.1093/jac/49.1.161
11. Van Acker, R., Rahman, M., & Cici, S. Pros and Cons of GMO Crop Farming. Oxford Research Encyclopedia of Environmental Science. Retrieved 28 Jul. 2022, from https://oxfordre.com/environmentalscience/view/10.1093/acrefore/9780199389414.001.0001/acrefore-9780199389414-e-217.
12. Van Acker, R. C., McLean, N., & Martin, R. C. (2007). Development of quality assurance protocols to prevent GM-contamination of organic crops. In J. Cooper, U. Niggli, & C. Leifert (Eds.), Handbook of organic food safety and quality (pp. 466–489). Boca Raton, FL: CRC.
13. Dunn, S.E.; Vicini, J.L.; Glenn, K.C.; Fleischer, D.M.; Greenhawt, M.J. The allergenicity of genetically modified foods from genetically engineered crops: A narrative and systematic review. Ann. Allergy, Asthma Immunol. 2017, 119, 214-222.e3, doi:10.1016/J.ANAI.2017.07.010.
14. Butler T, Reichhardt T. Long-term effect of GM crops serves up food for thought. Nature. 1999;398(6729):651–653. doi: 10.1038/19348.
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16. Séralini, GE., Cellier, D. & de Vendomois, J.S. New Analysis of a Rat Feeding Study with a Genetically Modified Maize Reveals Signs of Hepatorenal Toxicity. Arch Environ Contam Toxicol. 52, 596–602 (2007). https://doi.org/10.1007/s00244-006-0149-5
17. Wang, H., Kim, DW, Lee, IS, & Kim, IH (2019). Non-GMO beet pulp and canola meal cornsoybean meal diet ingredient has comparable effects as that of GMO corn-soybean meal diet on the performance of sows and piglets. Agricultural Science Research, 46 (4), 715–722. https://doi.org/10.7744/KJOAS.20190042
18. Alexander Y. Panchin & Alexander I. Tuzhikov (2017)Published GMO studies find no evidence of harm when corrected for multiple comparisons,Critical Reviews in Biotechnology,37:2,213-217,DOI: 10.3109/07388551.2015.1130684
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