by Charles Xu
figures by Krissy Lyon
Summary: People are concerned about the potential of GMO food to cause allergies. However, the technology used for making GMO crops does not necessarily make us more vulnerable than conventional breeding. Comprehensive evaluation for market approval, food safety surveillance, and adequate labeling could minimize the health risks of food allergies. Moreover, further development of technology might even enable us to remove the common allergens in our food.
In the autumn of 2000, a California woman named Grace Booth went into anaphylactic shock after eating three corn tacos; after ruling out all other food allergies, she became suspicious about the corn in the tortillas. Earlier that year, the consumer group Genetically Engineered Food Alert found that some Taco Bell shells, along with other corn products, contain a pest-repelling protein called Cry9C. Originally from common soil bacteria, Cry9C can specifically destroy insect intestine and was introduced into StarLink GMO corn to kill predatory caterpillars (see this article). The StarLink corn had only been approved for animal feeding, and was never intended for human consumption because of concerns that Cry9C would be difficult to digest and cause an allergic reaction. However, it still entered the human supply due to cross-pollination when the GMO corn was planted too close to unmodified crops, and the tortillas that Grace ate were soon recalled due to contamination from a GMO product (Figure 1).
Although the Food and Drug Administration (FDA) did not find a direct link between Cry9C and allergic reactions in the consumers who claimed to have ingested StarLink corn, this recall spurred public discussion about the health risks of GMO foods. As a result, the scientific community is often asked if GMO foods make us more vulnerable to allergens, and how we can mitigate these potential risks.
Figure 1. Contamination of non-GM corn with GM corn StarLink containing the Cry9C protein may have caused an allergic reaction in one Taco Bell customer. It was not possible to prove a direct link between the Cry protein and the allergic reaction, but many believe this protien to be the culprit. Importantly, although many people ate the contaminated tacos, they were not all affected. Like any allergy, only those allergic to the allergen present in the contaminating corn would have an adverse reaction.
Allergens in GMO vs. non-GMO foods
An “allergy” is a hypersensitive immune response that occurs when a person comes into contact with specific substances called allergens. Allergies can lead to red eyes, itchy rash, swelling, runny nose, and breathing difficulties. Allergies are very common, and food-specific allergies affect 240-550 million people in the world. In the US, 1 in every 13 children has a food allergy, and the prevalence of childhood allergies has increased by more than 50% in the last 20 years. A combination of host and environmental factors determine the intensity of allergic reactions: increased vulnerability can be attributed to various factors including changes in lifestyle, hygiene, diet, and physical activity. However, there is no evidence that GMOs are any more or less allergenic than their non-modified counterparts.
Ninety percent of food allergies are caused by the common allergens in peanuts, tree nuts, milk, eggs, wheat, soy, shellfish, and fish. In 1996, researchers found that the main allergen from Brazil nuts retains its allergenicity after being transferred into a GMO soybean; the Brazil nut GMO soybean has never been approved for the market, and 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. Potential allergenicity is then further analyzed with comprehensive experiments. Additionally, as part of post-marketing monitoring, randomly sampled consumers are examined to detect previously unidentified allergenicity. Currently, around 30 GMO crops have received approval in the US, and most of our corn, soybeans, and cotton are GMO crops. To date, no allergens have been found in GMO products approved for human consumption.
Regulation of Allergens
Since GMO market approval is under strict regulation, we should probably be more concerned about contamination from unauthorized GMOs (such as StarLink corn) than about allergies to common GMO foods. GMO plants can spread their genes to conventional crops through cross-pollination. To avoid such occurrences, there are guidelines stipulating that GMO plants should be physically segregated from the closely related plants by a buffer zone that is sized proportionally to how far the pollen can travel; however, it must be considered that not all farmers will obey these guidelines, and some pollen can travel unexpectedly long distances via bees or other pollinators. With this in mind, the European Union (EU) scientific committee on plants states that contamination is unavoidable, and therefore, the consequences of contamination should be considered before market approval. However, if contamination occurs, it is possible to eliminate the food containing the suspicious or unexpected allergens via a robust safety surveillance system. In fact, the scrutiny for common allergens in our food supply has been in practice long before the emergence of GMO foods. After the recall of StarLink corn and the subsequent ending of its planting, the presence of Cry9C residues was monitored for many years until the corn supply was essentially free of StarLink.
As different individuals can be allergic to different foods, the major risk of food allergy comes from unwitting ingestion of the allergen. Therefore, it will be helpful for every consumer to know the exact composition of their food, where it is genetically modified or not. Mandatory labeling of GMO ingredients, which has been required by law in the EU but not the US, could help consumers identify the potential allergens and facilitate the recall process, if necessary. However, unless it involves common allergens such as gluten and peanuts, the labeling of even non-GMO food is often inadequate. Thus, there does not appear to be particular bias towards poor labeling in GMO foods only.
Figure 2. GMOs could be used to remove allergens from food, allowing those with allergies to eat food that they previously couldn’t. This technology is still in development, but it could be the future of staying allergen-free.
Removing Allergens by Genetic Engineering
With appropriate oversight, the technology used for engineering GMO crops need not cause more allergic responses than conventional breeding. On the contrary, we rely on GMO technology to overcome some of the most difficult challenges for food safety. For example, to prevent contamination, scientists are engineering GMO crops to only self-pollinate or fertilize with manual assistance[1,8]. Additionally, it has recently been reported that scientists can reduce or remove the common allergens in our crops with GMO technology (Figure 2). This was most strikingly demonstrated by an international team of researchers that suppressed the enzyme responsible for making gluten in wheat, leading to a resulting GMO wheat with a 76.4% reduction of gluten in its seeds. Admittedly, there is still a long way to go before we could enjoy a roll of bread made from gluten-free GMO wheat, but such preliminary success has inspired us to believe in that future development of GMO technology could become a solution to, rather than a cause of, food allergies.
Charles Xu is a Ph.D. candidate in the Biological and Biomedical Sciences program at Harvard University
This article is part of the August 2015 Special Edition, Genetically Modified Organisms and Our Food.
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