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Genes are series of chemicals, called "nucleic acids," in DNA (see Figure I). The nucleic acids are like letters in an alphabet three of which makes a little "code" in a row and the code stands for a particular amino acid. Amino acids are the building blocks of proteins and proteins are the building blocks of living organisms. Proteins form the structures of livings, and form the enzymes they use to perform the chemical reactions needed to stay alive. The order of the "nucleic acids" in DNA lies beneath the order of amino acids in proteins whereas the order of amino acids affects what the protein will do. Our bodies contain more than a million different kinds of proteins, each with diverse jobs.
Figure I: A gene as a part of DNA (Source: U.S. National Library of Medicine)
What is genetic modification?
According to Australia's national science agency The Commonwealth Scientific and Industrial Research Organization (CSIRO), genetic modification (GM), also called genetic manipulation (GM) and genetic engineering (GE), refers "to the use of modern biotechnology techniques to change the genes of an organism, such as a plant or animal." The agency also makes a definition of genetically modified organism (GMO) as "a plant, animal or any other organism that has been changed using genetic engineering." This report focuses solely on GM organisms that are used as food. GM organisms that are used as ingredients of various products other than food, such as cosmetics, are excluded from the scope of this study.
What is genetically modified food?
A genetically modified food (GMF) is a product of recombinant DNA biotechnological procedures that allow the genetic structure of an organism to be modified either by integrating genes from other organisms or by rearrangement of genes already present, resulting in the expression of attributes not found in the original organism (Schneider & Schneider, 2009). Foods using GMF as ingredients are also considered as genetically modified.
According to the "Engineered Foods Allowed on the Market" chart prepared by the Union of Concerned Scientists (UCS); alfalfa, canola, corn, chicory, cotton, flax, papaya, potato, rice, soybean, squash, sugar beet and tomato can be produced as GMF (see Figure II).
Figure II: Examples of GM crops
However, GMF is not limited to this list, since not only direct consuming but also indirect consuming of these crops as ingredients in the processed foods is very common.
EFFECTS OF GENETICALLY MODIFIED FOOD ON HEALTH CARE
There is no consensus on the health issues associated with the consumption of GMF among the non-governmental organizations. For instance, while the US pro-GM group AgBioWorld argues that all GMF currently on the market were proven safe, the Organic Consumers Association points out that long-term health risks have not been properly investigated. Based on the World Health Organization (WHO), the three major topics currently under intense scrutiny are the ability of GMF to intensity or provoke allergic reaction (allergenicity), to transfer their genes to humans, and to contaminate conventional food by out-crossing.
Food allergies are reactions triggered by specific food items or ingredients that are harmless to the general population (Sampson & Burks, 1996). Most allergic reactions are mediated by allergen-specific immunoglobulin E (IgE) antibodies, which cause a rapid hypersensitivity beginning few minutes or hours after ingestion. This type of reaction requires an initial exposure to this food item to develop allergen-specific IgE antibodies, which are bound to the surface of immune cells, including mast cells. When this food item is ingested again, the allergen binds to these IgE antibodies to trigger the cellular release of mediators that will induce symptoms characteristic of allergic reactions, ranging from mild to life threatening, depending on the individual.
These IgE-mediated allergic reactions are more common in children than in adults, affecting nearly 8% of infants before the age of three (Bock, 1987). According to the Codex Committee on Food Labeling, the most common items triggering this type of reaction are eggs, milk, wheat, peanuts, soybeans, tree nuts and shell fishes (Hefle, Nordlee, & Taylor, 1996) (see Figure III). In addition, the oral allergy syndrome (OAS), caused by fresh fruits and vegetables, is fairly common (Ortolani, Ispano, Pastorello, Bigi, & Ansaloni, 1988). The symptoms are generally mild and confined to the throat. Most allergens are denatured by cooking or digestion, but OAS may also induce a systemic reaction (Ballmer-Weber, Vieths, Luttkopf, Heuschmann, & Wuthrich, 2000).
Figure III: Most common sources of food allergies
True food allergies also include the delayed hypersensitivity reactions which are felt at least eight hours after ingestion (Sampson, 1990). In infants, this food-induced enteropathy is generally caused by milk or soy. In adults, the most common type is gluten-sensitive enteropathy, also known as celiac disease (Vilppula et al., 2009). It is now estimated that celiac disease affects 1% of the western population (P. H. Green & Cellier, 2007). The gluten-containing cereals identified by the Codex Committee on Food Labeling include wheat, rye, barley, oats and spelt. Since gluten is omnipresent in our daily diet, many cases of celiac disease remain unreported. Currently, the most accurate test is the detection of transglutaminase-specific IgA.
Celiac disease develops from a mixture of environmental and genetic factors, and is mediated by the immune cells, named T lymphocytes, lodged in the intestinal wall (May-Ling Tjon, van Bergen, & Koning, 2010). When exposed to gluten (gliadin), these cells mount an exaggerated inflammatory reaction which causes damage to the intestinal wall. The long-term consequences of this allergenicity include nutrient malabsorption, anemia, diarrhea, osteoporosis, and neurological symptoms. Since most compounds causing food allergies remain unknown, the only remedy is a strict diet avoiding the specific food item. This situation is complicated by changes in food distribution and formulation, and the introduction of new allergenic food items in the market place. For instance, the recent arrival of the kiwi brought additional sources of food allergens in America, whereas the larger distribution of ethnic foods, like sesame seeds, contributes to the constant rise in allergic sensitivity to certain foods (Ballmer-Weber & Hoffmann-Sommergruber, 2011). Our continuous exposure to novel proteins may cause unpredictable complications, in particular allergenicity.
There is raising concern that GM crops may increase food allergenicity. For instance, soybean crops were modified to raise their content in sulfur-rich amino acids by gene transfer from Brazil nuts. However, this technique also transferred an allergen from the nuts, resulting in an increased allergenicity of the soy products (Lehrer, Horner, & Reese, 1996). These findings are acting like a cold shower in view of the recent discovery that soy may prevent or treat various forms of cancer (Raffoul et al., 2007) (Singh-Gupta et al., 2011).
Another very important issue with GMF is the introduction of unknown allergens. The genes transferred into GM crops are often derived from fermentation organisms which generate toxic substances (see Figure IV). For instance, certain GM cotton and corn crops are genetically engineered to produce their own pesticide, which kills the bug at first bite. This Bt toxin, produced by Bacillus thuringiensis, is commonly used by organic farmers as natural insecticide (see Figure V). However, GM crops contain toxin concentrations a thousand times higher than the soil. Moreover, studies confirmed that even lower concentrations are harmful to humans. In 1985-1986, when the Bt toxin was sprayed over Oregon to eradicate the gypsy moths, over 500 people reported allergy or flu-like symptoms (M. Green et al., 1990). While a recent study conducted in the sheep suggests that the ingestion of Bt toxin-containing GMF does no constitute a health risk (Anilkumar et al., 2010), the allergenicity reported in Oregon still raises concerns.
In 2005, GM soybeans were reported to contain two new allergens and seven times higher levels of their allergen, named trypsin inhibitor (Yum, Lee, Lee, Sohn, & Kim, 2005). In addition, certain individuals developed an allergic reaction to GM soybean, but not to non-GM soybeans. This is why each new protein should be tested for their allergenicity by comparing their structure with known allergens, or by the immune reactions induced in animals.
Interestingly, scientists are currently investigating methods to eliminate allergenic proteins from GM crops (Riascos, Weissinger, Weissinger, & Burks, 2010). The first strategy involves the selection of hypoallergenic legume crops, while the second requires genetic transformation to prevent the expression of the genes encoding the allergenic proteins. Both approaches were recently used to produce soybeans and peanuts with lower contents in allergenic proteins, but whether these products induce significantly milder allergic reactions remains to be documented.
Figure IV: Altering gene expression in crops
The unregulated use of antibiotics in medical research, medicine and animal care constitutes the main cause of the increasing antibiotic resistance. With respect to GMF, concerns have been raised regarding the common practice of plant selection based on antibiotic resistance genes. The transfer of antibiotic resistance from GMF to our body, or the bacteria inhabiting our digestive tract, could potentially be harmful. On the other hand, ampicillin and penicillin resistance occur naturally in many soil bacteria, and we ingest over a million antibiotic-resistant bacteria every day.
Figure V: Plants genetically modified to resist pesticides
In fact, our digestive enzymes are believed to be very efficient in degrading bacterial DNA. As such, the consumption of GMF is an unlikely route for the acquisition of antibiotic resistance. Alternatively, a recent study demonstrated that the gene inserted into GM soy may enter our intestinal bacteria and continue to produce the protein (Netherwood et al., 2004). Consequently, our intestinal bacteria may produce and release harmful GM proteins within our digestive tract long after we stop consuming GMF. In essence, our intestines are turned into living pesticide factories.
Closely related plants can hybridize each other when grown in proximity, thereby exchanging their genetic material to generate hybrids, such as the various colors of corn (see Figure VI). This spontaneous process of out-crossing also takes place between transgenic plants and conventional plants. Sometimes, the pollen of a domestic plant may travel several miles into the wind before it can fertilize another plant.
Figure VI: Plants genetically modified by out-crossing.
The unintentional airborne transport of genes between GM crops, and from GM crops to conventional crops, may have unpredictable adverse effects on our health. For example, a case of out-crossing was reported when trace amounts of a GM maize variant only approved for feedstock was detected in maize products intended for human consumption (Van de Wiel & Lotz, 2006). Several countries have adopted various strategies to reduce mixing, including distancing non-GM and GM crops. Also, consumers are given the choice between genetically-enhanced or traditional products, as producers maintain separate production chains. There are several studies, such as Co-Extra, SIGMEA and Trans-container, which are assisting farmers in their efforts to avoid mixing of transgenic and non-transgenic products.
The health risks associated to the consumption of GMF are not limited to the increase or induction of allergic reactions, and to the transfer of toxic genes to our intestinal bacteria. Animal studies showed that the ingestion of GM corn reduces the capacity of the liver to metabolize lipids and carbohydrates, which causes malabsorption of nutrients. Furthermore, GMF induce oxidative stress and cellular responses that could accelerate aging (Kilic & Aday, 2008; Malatesta et al., 2008). Other organs are also affected, including the kidney, pancreas and spleen (Finamore et al., 2008). In addition, the expression of nearly 400 genes are affected in mice fed GM corn, some of which regulate cholesterol synthesis and insulin levels (Velimirov, Binter, & Zentek, 2008). While the impact of these various effects on our health remains to be documented, it is clear that GM foods can no longer be considered risk free.
The world renowned biologist, Pushpa M. Bhargava, analyzed over 600 scientific publications, and concluded that GMF is a major factor in the rapid and consistent deterioration of Americans' health. Furthermore, the long-term frequent ingestion of GMF may even affect our fertility. A recent study, conducted in mice, demonstrated a direct relationship between GM corn consumption and infertility (Velimirov et al., 2008). They reported a significant reduction in litter size between generations, and the animals were also progressively smaller. As evidence on the devastating effects of long-term GMF consumption for future generations is emerging, The American Academy of Environmental Medicine (AAEM) urges "Physicians to inform their patients about the severe health risks of GM foods, and to avoid them as much as possible. They conclude that, "There is more than a casual association between GMF and adverse health effects. There is causation," identified using scientific criteria.
Despite these well grounded risk assessments, the biotechnology industry maintains that GM enhanced crops are the ultimate solution to eliminate starvation around the world. According to the International Service for the Acquisition of Agri-biotech Applications (ISAAA), the number of acres devoted to GM crops worldwide has reached a billion in 2010, which represents a 10% increase since 2009. On the other hand, Europe has reduced its production of GMF by nearly 30%, based on their own assessment of the health risks. Their tendency is likely to continue, as the new legislation allows members to ban GM crops without any scientific justification.
Worldwide growth of GM crops is believed to have positive and negative impacts on our environment. For example, the use of GM crops engineered with their own Bt toxin will reduce the number of pests and the need for farmers to spray insecticides. Also, herbicide resistant GM crops allow for a more efficient control of weeds. On the other hand out-crossing may introduce new species of weeds resistant to herbicides, much like antibiotic resistance. Another understated future consequence of GM crops is that patent laws are gradually giving developers control over our food supplies. The cost of food may eventually become dictated by a few men with deep pockets, much like the cost of crude oil.
Figure VII: Worldwide distribution of GM crops.
According to World Health Organization (WHO), allergenicity, gene transfer and out-crossing are the three major topics subject to discussion about the effects of consuming GMF.
There is raising concern that GM crops may increase food allergenicity and unknown allergens are proven to be introduced by GMF whereas scientists continue to investigate methods to eliminate allergenic proteins from GM crops. Concerns have also been raised regarding the common practice of plant selection based on antibiotic resistance genes. Contrary to this belief, the real danger is not the possibility of acquiring antibiotics resistance. It is, indeed, the possibility of genes that are injected to a GM crop entering our intestinal bacteria and making it produce and release harmful GM proteins within our digestive tract long after we stop consuming GMF. The third major debate issue is the spontaneous process of out-crossing which also takes place between transgenic plants and conventional plants. The unintentional airborne transport of genes between GM crops, and from GM crops to conventional crops, may have unpredictable adverse effects on our health.
Beside all these, recent studies show that internal organs can show malfunctioning due to the GMF consumption. Though, there are many research studies yet to be and should be done in order to properly document the long-term effects of consuming GMF, in the light of the current information we have, the risks of consuming and growing GMF seem to surpass the benefits we obtain.