Genetically Modified Food

1、Genetically Modified Food: Is it safe to Eat Genetically Modified Crops? by Rich DeemIntroduction1 The safety of genetically modified (GM) foods has been decried by many from the nutritional health community. One article, entitled, "Genetically Modified Foods Pose Huge Health Risk" claims

2、that thousands of animals fed genetically-modified organisms (GMO) have died and that "post mortems showed severe irritation and black patches in both intestines and liver."1 This same article claims "that genetically modified organisms (GMOs) are a major contributor to the sharply de

3、teriorating health of Americans."1 The controversy came to a head in November, 2012 in California with a vote on a proposition, which would have required labeling of GMO food. The proposition was sponsored by the members of the organic food industry and trial lawyers, who would have benefited b

4、y suing small businesses who failed to comply with the extensive labeling requirements. Although the proposition failed, the so-called dangers posed by genetically modified food were placed before the voters during the extensive advertising campaigns. It is estimated that 50-70% of all food consumed

5、 in the United States contains at least some components that come from genetically modified crops. This page represents an unbiased analysis of the risks and benefits of producing and consuming genetically modified organisms.What are GMO?2 Although human beings have been modifying the genetics of pl

6、ants and animals for thousands of years through selective breeding, genetic modification, as now applied, refers to the introduction of specific foreign genes into an organism's genome through the techniques of molecular biology. Genetic engineering of organisms began in earnest in the 1970s wit

7、h the ability of scientists to clone genes and insert them in bacteria. Such "transgenic" organisms could be made to produce the gene products of the inserted gene, allowing scientists to produce drugs such as human insulin and other biochemical products with ease. Soon after, scientists w

8、ere inserting genes into mouse embryos to produce transgenic animals for research. Other molecular biology techniques allowed scientists to "knockout" genes of interest to see what effect their removal had upon specific disease processes. In our laboratory, we use cloning and genetic engin

9、eering to produce both transgenic and knockout mouse models to study inflammatory bowel diseases肠道炎症. Obviously, not all genetic modification of organisms is bad, since these GMOs have led to breakthroughs in medical research.Genetically modified crops3 Food crops have been genetically modified for

10、several reasonsmost of which produce a financial benefit to farmers and the chemical companies that produce the GMOs. In nearly all cases, these benefits are achieved indirectly by increasing crop yields through resistance to diseases and pests or by allowing reduced use of herbicides to control wee

11、ds and unwanted plant growth. Monsanto has produced "Roundup Ready" seeds whose plants are resistant to the herbicide Roundup. Roundup consists of glyphosate甘油, which kills plants by interfering with the shikimate pathway (which produces aromatic amino acids芳香族氨基酸) in plants. Since animals

12、 don't posses the shikimatepathway, but get aromatic amino acids from their diet, Roundup is not toxic to human beings. A favorite gene to incorporate into plants to confer pest resistance is the bacterial toxin from Bacillus thuringiensis 苏云金杆菌(Bt). This toxin binds to a specific receptor 受体on

13、the surface of midgut epithelial 分泌薄壁细泡cells of certain orders of insects, disrupting digestion and killing the pest. Since this receptor is not found in vertebrates脊椎动物，such as humans, it is non-toxic, so it produces no harm. The advantage of incorporating Bt toxin into the plant is that only pests

14、 who eat the crops are killed. Since the 1930s, Bt toxin has been used as an insecticide, being sprayed on plants, killing pests along with beneficial insects that accidentally ingest the toxin.In addition to pest and herbicide resistance, scientists have altered plant-produced oils to produce healt

15、hier products, added vitamin A to rice ("golden rice"), and conferred resistance to viral attack. Genetic engineering of papaya saved the Hawaiian papaya industry from extinction due to infection with Ringspot virus环斑病毒 in 1998.2To date, several crops have been genetically modified, a few

16、of which now account for the vast majority of those crops now cultivated in the United States. In the United States, nearly all corn, soybean and cotton crops are now genetically modified. In Canada, nearly all rapeseed 油菜籽(canola) is genetically modified. Other genetically modified crops include:Ge

17、netically Modified Crops (as of December, 2012)3See Pic1Genetically modified animals4 Enviropig is a genetically modified pig that produces the enzyme phytase肌醇六磷酸酶, which allows the pig to digest phytic acid, which contains a form of phosphorus 磷that is normally indigestible.This results in reduced

18、 phosphorus being released into the environment, reducing pollution of waterways. Another novel idea in genetic engineering was the cloning of pigs that were rich in omega-3 fatty acids.5 With this GM pig, you could get healthy omega-3 fatty acids by eating bacon, instead of smelly fish. Genetic eng

19、ineering has been used to alter cows so that they produce milk that is free of -lactoglobulin乳蛋白 (which many people are allergic to) and high in casein protein酪蛋白.Other cows have been genetically modified to produce milk that is nearly identical with human milk,7 which would allow mothers who cannot

20、 nurse the opportunity to give their infants milk that is more "natural" than standard baby formula. As of this writing, none of these innovations have been approved for human consumptionFrankenfish地狱鱼5 Genetically modified crops have produced not nearly the amount of controversy as the fi

21、rst animal genetically modified for human consumption. Affectionately referred to as "Frankenfish," this genetically modified AquAdvantage salmon was so controversial that the FDA failed to take action on its approval for market in 2010, requiring more study. What did AquaBounty do that wa

22、s so controversial? They took an Atlantic salmon (which are already extensively grown in farms) and added a growth hormone regulating gene from a Pacific Chinook salmon王鲑 and a promoter gene from an ocean pout大头鱼. So, instead of growing only during warmer months, the AquAdvantage salmon will grow al

23、l year long, achieving maturity in about half the time as wild Atlantic salmon. Although these genetically modified salmon could probably out-compete wild salmon because of their high growth rate, they are provided by AquaBounty as sterile females, to prevent breeding, should they be inadvertently r

24、eleased into the wild. Despite these precautions, activist groups, along with the Alaska salmon fishing lobby, convinced the FDA not to approve AquaBounty's application. From a scientific perspective, the genes inserted into the genetically modified salmon are naturally-occurring, and have been

25、eaten in their respective host species without incident. The FDA finally released the environmental report for AquAdvantage salmon immediately before Christmas, 2012, although the report itself was dated May, 2012.GM pets/flowers6 Fluorescent proteins 荧光蛋白have been used for years in molecular biolog

26、y research to report expression of genes to which it is attached. When the gene of interest is transcribed, the fluorescent protein is also expressed, which shows up as a fluorescent glow that can be measured. Most of these fluorescent proteins have been isolated from species of jellyfish. Entrepren

27、eurs have incorporated different fluorescent protein into zebrafish斑马鱼 and tetras脂鲤 to create transgenic pets. These "Glofish" have been marketed as unique tropical fish, notable for their stunning fluorescent colors.9 In addition to the stunning colors of zebrafish, scientists have geneti

28、cally engineered colors in flowers that aren't found in nature. Examples include the Blue Rose Applause and Moonshade Carnation.Can GMO foods harm people?7 For a number of GM crops, the genes/gene products never enter the food supply, since those parts of the plants are removed during processing

29、. For example, sugar from GM sugar beets is chemically identical to non-GM sugar. Likewise, oils purified from GM canola, soybean, cottonseed, and corn is identical to non-GM oils. Much of the corn crop is dedicated to generating ethanol乙醇, which, of course, is identical to non-GM ethanol. It has no

30、t been noted that ethanol from GM corn adversely affect automobile performance compared to non-GM ethanol. Genetically modified Bt cotton is worn, rather than ingested, and there have been no reports of adverse effects of wearing GM clothing. For GM crops in which whole plant cells are ingested, the

31、 genes and gene products are usually destroyed through digestion in the stomach and small intestine. So, it is unlikely, even in theory, that eating GM crops can harm human beings.GMO concerns and studies8 Concerns over the safety of genetically modified organisms extends across much more than just

32、food safety. Supporters of the environmental movement are concerned that GMO might escape into the wild and alter ecosystems. Another concern is that genetically modified genes might experience horizontal gene transfer through bacterial or viral vectors and end up in organisms for which they were ne

33、ver intended. These issues are dealt with below.Food safety9 In the United States all applications for the approval of GMO released for public consumption are handled by the FDA. Development and testing of a new GM crop typically requires 8 to 12 years, including more than 4 years of safety and envi

34、ronmental testing, before regulatory approval and commercial release.No particular food is safe to eat for all human beings, since about 6% of the human population has allergies to one or more food groups. FDA testing for food allergies to GM foods is identical to similar testing for non-GM foods. A

35、ny gene products found in GM food that is not found in non-GM food must have its structure analyzed to determine if it matches any known allergen (containing a sequence greater than 35% identical to any 80-amino-acid segment of known allergens, where an average protein contains hundreds of amino aci

36、ds). In nearly all instances, commonly inserted genes would never be expected to be similar to food allergens. However, if a match were found, the protein would have to be tested with sera血清 from allergy sufferers to establish allergenicity致敏性. A GM product that exhibits "substantial equivalenc

37、e" to the non-GM variety is declared to be safe. There is no published evidence of allergic reactions to any GM protein or any adverse human health reactions associated with consumption of foods from GM crops since the introduction of GM products into the food supply.11 A test of the allergenic

38、ity of GM vs. non-GM soybeans was done in 2006, and scientists found no differences in the reactions of sera from allergy sufferers.12Scientific Studies on the Food Safety of Genetically Modified Crops See pic2Although there appear to be conflicting data about the safety of GM food, all the negative

39、 studies have come from one laboratory headed by Dr. Gilles-Eric Séralini at the University of Caen, France. The conclusions of those studies have been refuted by numerous scientists who have noted flaws in study designs and statistical evaluations.36 In addition, Séralini is funded by the

40、 Committee for Research and Independent Information on Genetic Engineering, in Paris, France, which opposes genetic engineering of crops.Environmental concerns10 Realistic environmental concerns over GM crops fall into two categories; (1) the development of resistance in Bt crop target organisms and

41、 (2) tolerance in weeds to complementary herbicides used in HT crops.37 Although concerns have been raised over the use of large-scale mono-crops, these concerns are not specific to GM modified crops, but apply to corporate farming in general. None of the crops in question are hardy enough to escape

42、 into the environment and compete with indigenous flora.The development of resistance to Bt toxin by pests was anticipated prior to commercialization of those crops. For this reason, Many crops include multiple variations of the Bt toxin in their products. In addition, all farms using GM Bt crops mu

43、st plant a small percentage of corresponding non-GM crop in the vicinity. In theory, these non-GM crops would attract pests, which would reproduce abundantly, overwhelming the gene pool of any potential Bt-resistant mutants.Another question is whether GM crops containing Bt toxin affect insect preda

44、tors who feed on pests that eat GM crops. For most studies, ingestion of pests that eat GM crops does not negatively impact predator insect species.38 However, some predator species have been negatively impacted, although those impacts were probably less than they would have been with conventional c

45、rops in which pesticides were used indiscriminately.Gene flow and gene transfer11 Concern has been raised about genetic mixing of GM crop genes with wild, related species. For most crops, no sufficiently-related natural species still exist. However, crops related to the Brassica and Beta species (ra

46、peseed, aka canola, and sugar beets) do have wild relatives. In 1999 scientists showed in the lab that pollen from rapeseed could fertilize wild turnip to produce viable seeds.39 However, the transfer of GM genes into wild populations has never been demonstrated to have occurred in nature.Unintended

47、 genetic changes12 Although the genes being introduced into plants are highly characterized and defined, the process of gene insertion and tissue culture can result in unintended genetic changes. Plants are transformed by culturing individual cells in tissue culture and inserting the desired trait i

48、nto the DNA by one of several methods. The most common is through infection with genetically transformed Agrobacterium tumefaciens, a bacterium that infects plants. Through the infection process, the desired trait is incorporated into the host DNA. A second mechanism is through particle acceleration

49、, which physically pushes small particles into the plant cell nucleus where the gene is incorporated. The desired genes are usually linked to specific antibiotic resistance genes so that transformed plant cells can be selected through resistance to antibiotics that are included in the tissue culture

50、 medium. The mechanism by which the foreign genes are incorporated into the host genome are not well understood. However, since much of the eukaryotic genomes consist of non-critical DNA segments, random incorporation does not usually lead to adverse effects on the host. Cells in which the foreign g

51、enes are incorporated into critical genes will tend to produce a lethal mutation that prevents the cell from growing. However, it is theoretically possible that random incorporation of a GM gene could lead to disregulation of a particular gene, which could have unintended consequences. However, such

52、 events would be expected to be very rare. With the advances in gene array technology, scientists can now explicitly examine gene expression from all the genes in GM vs. non-GM crop species. The results of numerous studies show that virtually all gene expression is identical between GM and non-GM pl

53、ants.40 In fact, studies found greater differences in gene and protein expression as a result of crop differences between farms than differences between GM and non-GM crops.40 However, the act of cloning individual plant cells in tissue culture probably results in more changes to the genome than the

54、 actual genetic transformation itself.41 In order to minimize these differences, once the desired trait is selected, the new variety is conventionally back-crossed with normal plants to produce a GM variety as similar as possible to the non-GM original. An extensive review of GM-crop risks concluded

55、, "there is no indication from the molecular characterization of GM plants that the insertion of GM DNA as such poses a long-term risk due to new mechanisms of genetic instability or re-arrangements."37In the last year, a newly invented technology allows scientists to accurate choose where

56、 genes are inserted into the host species. The TagMo process involves exact chromosome breakage and insertion of genes into the target DNA.42 Once this technique is broadly adapted, unintended genetics changes will be reduced to virtually zero.Economic benefits of GMO13 The main benefit of GM crops

57、is economics, since the nutritional component has largely gone unexploited. The political/social climate surrounding GMO must improve before companies would be willing to invest money into genetic engineering for enhanced food nutrition. The economics of GM crops was analyzed in a study of 196 publi

58、cations containing 721 entries for the statistical analysis in 2011.43 The meta analysis found that crop yields for GM Bt cotton were up to 50% higher than conventional cotton (in India). However, yields in developed countries were only 1-28% higher, since pest management was aggressive before the i

59、ntroduction of GM cotton. However, reductions in pesticide costs range from 16% in the USA to about 70% in China. Yield levels of Bt corn are higher (5%-25%) compared to conventional maize, and along with lower pesticide costs, results in higher gross margins of 10%-17% for farmers. For GM soybeans,

60、 marginally increased yields and reduced pesticide costs did not make up for the higher cost of GM seed. In general, benefits of GM farming are higher in developing countries compared with developed countries. Overall, it was estimated that GM crops benefit farmers by $7 billion per year, worldwide.43Food l