May 2010 Issue

Are Genetically Modified Foods Safe?
By Karen Lilyquist, PhD, RN, RD, LD
Today’s Dietitian
Vol. 12 No. 5 P. 42

Suggested CDR Learning Codes: 2040, 2050; Level 2

Genetically modified (GM) foods are the focus of heated public debate concerning their development, production, sale, and consumption. The question is safety, and the two sides could not be farther apart. Moreover, the rhetoric seems to escalate with every research project, government ruling, or news story regarding them. Rather than shedding light on the subject, the two sides seem determined to apply heat to it. This article will define the issue and cite the best current research to address whether these foods are safe.

Proponents argue that GM crops offer many potential benefits over conventional crops, including decreased production costs, decreased pesticide and herbicide use, increased crop yield, and improved nutritional value.

According to opponents, the introduction of GM crops has been a disaster, posing serious threats to environmental and human health. They claim flawed research and inadequate regulation, especially in the safety assessment procedures, and focus on reports of potential organ and system toxicity.1

There seems to be no middle ground and without strong evidence-based reasons to ban GM products, their presence continues to expand. An estimated 60% to 70% of food products in local grocery stores contain at least one GM ingredient, but due to relaxed laws and regulations, the U.S. consumer has little knowledge of which foods contain these ingredients. More than 100 varieties of 50 different crops are available for cultivation. Soybeans, corn, rice, tomatoes, potatoes, and canola are all genetically engineered (GE) foods that have been approved for commercial use.

Background
A few definitions will aid this discussion. Deoxyribonucleic acid (DNA) is a nucleic acid found in all cells with the main role of long-term information storage. It provides a set of blueprints to construct cell components. The DNA segments that carry this genetic information are called genes.

In a genetically modified organism (GMO), the genetic material has been modified by any means. In a GE organism, the genetic material has been modified through the direct transfer or removal of genes. One such technique is recombinant DNA (rDNA), the splicing of two unrelated pieces of DNA to produce a new molecule that is replicated. The process allows selected genes to be transferred from one organism to another, even between nonrelated species, something that is not possible with conventional selective crossbreeding. So these transgenic organisms have a gene from a different organism inserted into them. The transferred gene (transgene), like all genes, carries the instructions for making a protein, which controls the GMO’s biological processes and determines its characteristics.

The purpose of the genetic modification is to introduce desired traits into the new organism. The use of gene selection to produce better foods and crop yields is not new. Yeast has been used for thousands of years in food preparation (eg, beer, bread), and plant breeders have used cross-fertilization of two closely related plants of the same species to produce desired characteristics in the offspring. No one questions the creation of hybrid strains in this way. It seems natural to identify plants with desirable characteristics and promote their reproduction. However, the use of horizontal gene transfer between species, altering DNA in a manner that cannot occur naturally, draws question.

Growing Trend
But while the questions mount, the steady progression of GE crops continues. U.S. farmers have adopted GE crops since their introduction in 1996 despite the controversy.2 Soybeans and cotton, genetically engineered with herbicide-tolerant (HT) traits, have seen the most rapid growth rate, followed closely by HT corn and insect-resistant corn and cotton. Insect-resistant crops contain the gene from the soil bacterium Bacillus thuringiensis (Bt) that produces a protein toxic to specific insects. Crops are protected over the entire life cycle.

Based on USDA survey data, the use of Bt corn grew from 8% of U.S. corn acreage in 1997 to 19% in 2001 to 63% in 2009. Bt cotton saw similar growth—from 15% of U.S. cotton acreage in 1997 to 37% in 2001 to 65% in 2009. HT soybean use went from 17% of U.S. soybean acreage in 1997 to 68% in 2001 to 91% in 2009. Plantings of HT cotton grew from about 10% of U.S. acreage in 1997 to 56% in 2001 to 71% in 2009. The acceptance of HT corn has accelerated in recent years, reaching 68% of U.S. corn acreage in 2009.3

Other GM crops that U.S. farmers have planted in the past 10 years include virus-resistant varieties of squash and papaya and HT canola. Some crops have been introduced only to be withdrawn from the market. For example, Bt potato varieties were available from 1996 to 2001. A tomato variety genetically engineered to remain on the vine longer was introduced in 1994, was available sporadically for several years, and then was withdrawn for safety reasons.

In contrast, the European Union (EU) has only one commercially grown GM crop: an insect-resistant corn. The cultivation of GM plants is legally possible in EU countries, but the stringent approval process and recently lifted de facto approval moratorium has kept commercially authorized GM products to a minimum. The EU, despite criticism, is set to approve a GM potato for use in livestock feed and industrial processes.

Better Nutrition Using rDNA Technology
GM proponents claim that GM crops substantially reduce the need for herbicides and pesticides. GM crops have inherent characteristics that allow broad spectrum synthetic products to be applied to the growing crop, killing the weeds and pests while leaving the crop unharmed. The initial intent of HT and insect-resistant genetic modification was to lessen the need for chemical application throughout the growing season.

Besides the cost and environmental advantages of not using herbicides and pesticides, the potential for enhanced nutrition has been another reason for the leap to GM foods. Of note, no commercially available GM food to date has more nutritional value than non-GM food.4-6 However, there are examples of how the technology might be used.

One is golden rice, a source of vitamin A due to the insertion of beta-carotene–producing genes into rice grains. All plants contain beta-carotene, a pigment needed for photosynthesis, but it is not normally found in nonphotosynthetic plant tissues such as seeds (eg, the grains of rice). Three genes were added to normal rice: two from the daffodil and one from a bacterium. The resulting hybrid rice contains four to five times the normal beta-carotene. A later modification raised that to 23 times normal. Now, rice alone could meet the total daily requirement for vitamin A for millions of people living in countries in which rice is a dietary staple. Estimates indicate that more than 3 million children worldwide experience stunted growth and blindness as a result of severe vitamin A deficiency. Recent studies suggest vitamin A can be produced directly within GM plants, but the results have yet to be published.

Iron deficiency is widespread in poorer countries. Pharmaceutical iron supplementation can be expensive and often alters a person’s sense of taste, leading to poor compliance. Food fortification presents problems as well; unacceptable color and flavor changes accompany iron compounds of relatively high bioavailability. Because it is a staple food for the most vulnerable people, rice has been considered as a vehicle for increasing iron consumption. Several factors complicate the process of increasing the iron content of food. Unlike beta-carotene, iron cannot be produced by the plant. And while iron is present in sufficient amounts in the soil, it is not easily accessible for plant uptake because most, if not all, is chemically bound or present in the wrong form. Moreover, intestinal absorption of iron is inhibited by phytate and in rice, iron is bound by phytate. There is ongoing research into the insertion of a phytase gene that would degrade phytic acid and thus increase the amount of iron absorption during digestion of this food. Another potential avenue is to increase the iron content of the rice by adding a ferritin gene from a bean. Further research suggests the possibilities of increasing iron uptake and transport with use of alternate genetic modification.7

Lycopene, a precursor to beta-carotene and a powerful antioxidant, is another component receiving attention. Lycopene’s role in reducing the risks of some cancers and retarding cell damage associated with disease and aging is well supported in research. Scientists from Purdue University and the USDA have developed a lycopene-enhanced tomato. Phytoene is the precursor to lycopene; phytoene desaturase is the enzyme needed for conversion. Lycopene production can be increased by inserting a bacterial gene that influences phytoene desaturase. (A more natural means of obtaining lycopene, according to the USDA, is to consume the heirloom variety called tangerine tomato, which contains a different, more bioavailable form of lycopene.)

Another example involves producing omega-3 long-chain polyunsaturated fatty acids in GM plants.8 The focus has been nutritionally enhancing vegetable oils by inserting specific marine-based fatty acids that do not naturally occur in plants. Despite the progress in obtaining useful levels in GM seed oils, the conversion involves a multiple-step process, which presents an ongoing challenge.

Health Concerns
Genetically modifying plants via gene insertion is new, so every step is subject to scrutiny and debate. Proponents note that greater than one half of U.S.-grown corn and 90% of soybeans are genetically modified and that consumers eat these foods without any evident health implications.3 But groups opposing genetic modification believe there hasn’t been enough concern about the potential health consequences of GM crops. They say, and some research confirms, the random insertion of foreign DNA into a plant may cause unexpected changes in cell function. How to evaluate those changes, if and when they occur, is problematic. Safety tests to date have been limited in duration, sample size, and rigor (with respect to statistical power), making an evaluation of potential toxicological risks difficult.9

Among the critical issues are the potential for allergenicity, the presence of antibiotic-resistant genes, and the introduction of novel genes.

• Potential for allergenicity: Most known human allergens are protein molecules. Thus, the introduction of new (novel) proteins into the food supply via genetic engineering raises legitimate concerns about the potential for allergenicity. One could argue that mixing genes from different food sources might increase the risk of additional food allergies.9

GM proponents point out, however, that genetic modification has an equal potential to reduce allergenicity, citing Dodo et al’s 2005 study in Curren Allergy and Asthma Reports. Thus far, only a limited number of reports support this effect, but further research is under way. For example, research on peanuts suggests that the structure of the protein can be altered so that it is less recognizable by immunoglobulin E antibodies and thus less apt to cause an allergic response in the host.

Ninety percent of known allergens come from eight foods and related products: peanuts, tree nuts, soybeans, wheat, cow’s milk, eggs, fish, and shellfish. The remaining 10% come from a large number of foods, with at least 160 documented sources.

The amino acid sequence of known allergens is established. The current criterion for comparing a novel protein’s amino acid sequences with the sequences of known allergens is sequence homology.10 If the proteins share eight contiguous, identical amino acids at any point in the protein structure, the novel protein is considered to have allergenic potential and is flagged for further study. If further testing indicates allergenicity, efforts to develop the GM product are typically abandoned.

In 1993, scientists detected allergenicity in a GM soybean containing a gene from Brazil nuts. The latter, a known allergen, is a source of high-methionine protein; soybeans contain little methionine. The resulting GM soybean plant, high in methionine, was also encoded with the allergen. The soybean was pulled from development and destroyed. Although this result was not fully unexpected, it brought questions regarding unknown allergens that may result from genetic modification and producing novel proteins. The food products that continue to be marketed must carry a label to alert consumers to the allergenic potential.

A pertinent concern is whether GM plants have more allergenic potential than those produced by conventional crossbreeding. Because there are so many unknowns, this will remain definitively unanswered. Taking a cautious stance, the National Academy of Sciences stated in its 2004 Safety of Genetically Engineered Foods: Approaches to Assessing Unintended Health Effects that “the process of genetic engineering has not been shown to be inherently dangerous but rather, evidence to date shows that any technique, including genetic engineering, carries the potential to result in unintended changes in the composition of the food.”

• Antibiotic-resistant genes: Another safety concern focuses on the potential that antibiotic-resistant genes used as selective markers in the rDNA process may be horizontally transferred to gut bacteria, altering the body’s response to antimicrobial therapy.1 Proponents maintain that the ingestion of the antibiotic-resistant gene would be minimal and likely degraded by stomach acid, limiting the health risks. Although the genes may present minimal risk, worry regarding long-term toxicity has been voiced, raising concerns related to unanticipated by-products and the safety of GM foods.

• Novel genes: The functional role of only a small portion of DNA is known. Although the gene is cut precisely from one organism, its insertion into a new organism is, in part, arbitrary. Because genes do not operate in isolation, the insertion disrupts the order of genes on the chromosome, changes their behavior in response to other genes, and can result in random and unanticipated changes in cell functioning—the creation of novel genes whose potential development during the rDNA process exists.

Opponents of genetic modification raise the issue of novel genes’ effects as they travel through the gastrointestinal (GI) tract. Proponents suggest that the novel genes are not different from the body’s own DNA and pose no greater threat than any other genetic material traversing the GI tract. Opponents want proof of no harm; proponents say no proof of harm exists. Is the absence of proof the same as the proof of absence?

Environmental Concerns
Debates of equal vigor surround the potential environmental hazards that GM crops pose. Among the most debated concerns are damage to soil, insects, and biodiversity and increased pesticide use. As with health risks, inadequate data exist and escalating the debate is the knowledge that as living organisms, GM components, once released into the environment, cannot be recalled.

• Soil damage: Living organisms contribute to soil productivity, providing essential nutrients and contributing to recycling waste. Research suggests that the Bt toxin is released into the soil through the plants’ roots. The toxin can remain active for more than 200 days, posing a risk to nontargeted insects and other organisms.

• Harmful to insects: GM crops are designed to kill targeted pests, but concern arises with respect to the unintended risk to other insects and species. Bt, the pesticide produced by most GM corn on the market, is found in both the plant’s cells and the pollen that is released by it. Research in 1999 suggested that monarch larvae feeding on plants dusted with Bt had a much higher mortality rate than those not exposed. Subsequent research notes the limited risk, but this research looked at short-term effects, not the effects of exposure to low-level toxin over time. A growing body of evidence suggests that GM crops are affecting other beneficial insects such as ladybugs, lacewings, and bees and possibly birds.

• Increased pesticide use: While GM proponents believe that GM crops are decreasing the need for herbicides and pesticides, opponents note that GM crops are effectively bringing about an agriculture dependent on the large application of synthetic chemicals. Crops modified to produce their own insecticides do so throughout a plant’s life cycle. Pests’ ongoing exposure to the toxin promotes resistance to it, and additional toxic chemicals will be needed.

• Creation of GM superweeds and superpests: Crops engineered to be herbicide resistant or produce their own pesticide pose further problems. Stronger weeds and pests will emerge, necessitating the use of more toxic chemicals. Wild mustard plants with increased herbicide-resistant traits have already been identified. Field tests indicate that common plant pests will evolve, completely immune to Bt sprays. Ultimately, organic and conventional farmers will be unable to cope with these weeds and pests.

Thus far, no catastrophic environmental impact has emerged as a result of the use of GM crops in the United States.11 This does not mean one can conclude that there has been no environmental impact. Environmental safety is difficult to assess; changes tend to occur over the long term rather than the short time that GM crops have been in widespread use. Subtle changes in plant or animal populations may not be overt enough to connect with the genetic modifications taking place. Systemic monitoring is limited; more time and data are needed before the true impact is revealed.

Consumer Confidence Issues
U.S. consumers are understandably cautious about a technology they are not familiar with and do not thoroughly understand. It is difficult to make an informed, rational decision about GM foods since studies concerning their safety are still few. Prudence suggests that the inadequate number of safety studies and lack of data indicating GM foods are unsafe should not be equated with proof that GM foods are safe for human consumption.1

Food producers confidentially perform regulatory tests prior to commercialization. Results are evaluated based on the concept of “substantial equivalence.” Crops vary in composition depending on differences in environmental and growth conditions, yet industry standards suggest that, save for a GMO’s transgene, GM and non-GM crops are substantially equivalent. Thus, only the GM ingredient is tested, not necessarily the GM food itself.

Substantially equivalent, however, has no scientific or legal meaning. It simply indicates that the crops are not significantly different. Inherent in the rDNA process is the introduction of genes from one organism into another. The insertion of genes can result in unintended effects. Scientists cannot predict all of the resulting changes in the host organism and thus cannot protect against them, nor can scientists protect against potential toxicity. Current toxicity testing is based on anticipated macronutrient and micronutrient compositions and known toxins.

Does using substantial equivalence as the basis for safety testing allow the necessary rigor or does it hide potential risks? Does it provide sound justification for not conducting toxicological and biochemical safety testing or does it allow for tests tailored to produce results conveniently suggesting the safety of a GM product? All are concerns voiced by those opposing the use of GMOs.

Even if one cites the lack of information as a reason to avoid GM foods, finding food with no GM ingredients may prove difficult. Because of the acceptance of substantial equivalence, U.S. regulatory agencies do not view GM foods as materially different from conventional varieties and labeling is not required.

In this area, opponents have been most vociferous. They want people to know what food products have been genetically modified.

Labeling of GM Foods
The FDA and the USDA have taken the position that the biotechnology processes do not make food safe or unsafe. In fact, a number of generally recognized as safe (GRAS) substances are produced using genetic modification.

The debate stems from the 1992 FDA policy that grants GRAS status to GM foods. It was assumed that the use of rDNA is a natural extension of conventional breeding techniques. For regulatory purposes, if a GM food product has the same composition, functional characteristics, nutritive value, and organoleptic properties (ie, taste, smell, mouthfeel) as a conventional product, then that GM food is considered to have substantial equivalence.12

To date, genetic alterations have been minor and genetic insertions have been specifically targeted, involving only one or a few genes. One can argue that a single gene affecting herbicide resistance, for example, should not affect the remainder of the plant genome, making the GM product substantially equivalent to the conventional plant in all other characteristics. Using this argument, the regulatory bodies considered the new crops to pose no new risks and thus enacted no new laws. Even more, existing laws do not require premarket testing or FDA approval of GM foods.

None of the products described previously—golden rice, low-phytate rice, lycopene-enhanced tomatoes, or highly monounsaturated soybean oil—would meet the criteria for substantial equivalence. The nutritive value of all of the described foods would be different from their conventionally produced counterparts and subsequently these foods would be subject to labeling. Current USDA laws require GM food labeling if:

• a food has a significantly different nutritional property;

• a new food contains an allergen that consumers would not expect to find in that food; or

• a food contains a toxin beyond acceptable levels.13

Food products outside these parameters have no mandates imposed.

GM products are likely to be found in foods containing these ingredients: canola oil and corn extracts, lecithin (in ice cream, chocolate, etc), and soya oil and flour (in breads, sausages, etc). Because the nutritional composition of the product has not changed, U.S. laws and regulations do not require labels. Labels on GM foods imply a health warning. If a nutritional or allergenic difference exists, current USDA regulations require a label to that effect.

Proponents of mandatory labeling champion consumers’ right to know. They argue that although GM foods are equivalent in many ways to their non-GM counterparts, they differ in one important way: DNA.12 Labeling is unclear and inconsistent from one country to another; consumers who have concerns about the unknown consequences or have religious and ethical concerns and wish to avoid GM foods altogether are left with few options.

Additional arguments in play include expense and logistical difficulties of labeling. Labeling all GM foods would impose a cost to all consumers. The anticipated benefit of consumer choice was not seen in the EU, Japan, and New Zealand where retailers essentially removed GE products from the grocery shelves because of negative consumer response.14 Moreover, consumers have the option of eating organic-certified foods that by definition cannot contain GM ingredients. The present food system infrastructure could not accommodate the need for separation of GM and non-GM food items.

Manufacturers have taken labeling into their own hands and created a market for non-GM foods. From 2000 to 2004, more than 3,500 products that had specific non-GM labeling were introduced. (This is in addition to organic foods.) There has been some attempt (mostly in the 1990s) to market GM foods, but this has been limited. For example, GM products include tomatoes (labeled as better tasting and having longer shelf life), canola oil (heat stable), and dietary supplements.

Global Famine
One of the loudest cries from proponents of biotechnology is the potential for providing enough food products for the world’s population. Most probiotechnology articles cite the rise in the world’s population (from the current 6.8 billion to an estimated 9 billion by 2050) and the need to increase agricultural production by 2.5 to 3 times. GM crops could increase crop yields and reduce crop loss by creating pest-resistant and HT crops. In addition, GMOs can increase production by making new crop land available. A tomato now exists that can grow in salty soil, thus utilizing land that would otherwise lay fallow. Moreover, GM crops are being developed that can withstand extreme drought and cold conditions.

Opponents suggest that the increased production of GM foods will not solve the world’s hunger problems. Arguing that enough food is produced on a per capita basis, they say global hunger exists because of insufficient food access, not insufficient production. Political, social, and economic barriers limit food access of the world’s poor. Thus, opponents to GMOs suggest it is inappropriate for people to be offered foods that may carry a health risk. In the highly charged world of biotechnology, such emotional political stances are not unexpected.

The Future for GM Foods
Future GM organisms will certainly include crops with even greater tolerance to disease and extreme weather.

A new area of development is edible vaccines, or vaccines inserted into a GM plant. For example, an edible vaccine against hepatitis B, a Norwalk virus, within a sweet potato or a banana has been developed. This type of vaccine can be shipped, stored, and administered at a low cost, increasing the application in low-income countries.

The development of plants with increased nutrient levels, fish that mature more quickly, and fruits and nuts that yield crops earlier than traditional organisms will likely continue. A newer technique is called MAS (marker-assisted selection). Combining traditional genetics and molecular biology, marker-assisted selection uses existing DNA, not transgenic DNA, for the selection of genes that control the desired traits.6

The application of genetic modification will continue. One cannot dispute the potential for increased nutritional content of foods, nor can one dispute the potential for more efficient food production. Still, the need for adequate examination of the potential human health and environmental risks related to the consumption of GM food products is clear.15

Biotechnological processes must be comprehensively evaluated if they are to be accepted by consumers and farmers alike and become a core of the food supply. Previous research has focused on human health and environmental issues in isolation and assumed the substantially equivalent clause; research has to step from the compartmentalized approach and look at the broad picture. We are challenged to assess the long-term effects of genetic modification—the known, the unknown, and the unpredictable.

What to Do in the Absence of Absolute Proof
Meanwhile, our clients will ask the simple question, “Are they safe?” Unfortunately, our response is necessarily equivocal, given the research, regulatory, and labeling concerns detailed previously. Absolute proof either way does not exist.

We can inform clients that organic-certified foods are an excellent choice for people who wish to avoid GM foods. Although organic-certified foods may not be conveniently available everywhere, they provide the only practical assurance that genetic modification has not been used.

For more information, check out the Pew Initiative on Food and Biotechnology, a nonprofit, nonpartisan research project whose mission is to inform the public and public policy makers about biotechnology issues. For those wanting to comment on regulatory issues, check out the agencies directly involved: the FDA, the USDA, the U.S. Department of State, and the World Trade Organization.

Passionate consumers may wish to support like-minded organizations in their advocacy and political efforts. For example, some environmental groups (eg, Greenpeace) are opposed to GM foods; other organizations (eg, the Council for Biotechnology Information) support GM foods.

— Karen Lilyquist, PhD, RN, RD, LD, has 21 years of nutrition practice experience. Since 2006, she has taught nutrition classes for the University of Phoenix, moderated teleconferences for the National Institute for Health Education & Training, and authored continuing education courses for Nutrition Dimension.

 

Learning Objectives
After completing this continuing education exercise, the student should be able to:

1. Define genetic modification as it applies to crops and food products.
2. Describe the recombinant DNA process that is used to produce genetically modified (GM) foods and identify foods that are currently available on the commercial market.

3. Identify hotly debated issues regarding GM foods and explain the pro and con positions.

4. Discuss the criteria for labeling of GM products.

5. Identify what options are available for the consumer who wishes to avoid GM foods.

 

Examination
1. A genetically modified organism (GMO) is defined as one:
a. in which genetic material has been modified by any means.
b. that has significantly higher nutritional value.
c. that has a gene removed from a different organism.
d. that has been grown in vitro.

2. All of the following crops have an herbicide-tolerant GM variety except:
a. soybeans.
b. cotton.
c. corn.
d. canola.
e. papayas.

3. How widespread is the use of GM seed in the United States?
a. At present, there is a ban on the use of GM seeds in the United States.
b. While it is legal to plant GM seeds in the United States, except for a few test plots, GM seed is not used.
c. At least 90% of the soybeans planted in the United States are GM seed.
d. Nearly all of seed (99%) used in the United States is GM.

4. While farmers may benefit from the cost and environmental advantages of not using herbicides and pesticides, consumers may benefit from the ___________ of GM foods.
a. increased availability
b. rich flavor and color
c. potential enhanced nutrition
d. allergen-free advantages

5. Golden rice is a highly touted GM food. This rice would be an excellent source of:
a. iron.
b. lycopene.
c. beta-carotene.
d. fatty acids.

6. Except for GMOs’ transgene, the FDA judges GM foods to be significantly equivalent to the conventional crop.
a. True
b. False

7. While proponents of the utilization of GMOs suggest that the small differences between GM and non-GM crops pose no biological implications, opponents voice concern related to:
a. allergenicity.
b. antibiotic-resistant genes.
c. novel genes.
d. All of the above

8. A GM food must carry a label if it has:
a. been grown in a field adjacent to a GM crop.
b. a significantly different nutritional property from its conventionally produced counterparts.
c. no difference in allergenicity or toxicity from its non-GM counterpart.
d. substantial equivalence to the non-GM counterpart.

9. A consumer who wishes to avoid GM foods can:
a. buy foods that are labeled all natural.
b. buy foods that are certified organic.
c. buy foods that are labeled GMOs rather than GM.
d. avoid corn and soybeans because those are the only GM seeds used in the United States.

10. Future GMOs may include crops with:
a. less tolerance to disease.
b. more herbicide resistance.
c. less nutritional value.
d. more pharmaceutical importance.

 

References
1. Dona A, Arvanitoyannis IS. Health risks of genetically modified foods. Crit Rev Food Sci Nutr. 2009;49(2):164-175.

2. U.S. Department of Agriculture Economic Research Service. Adoption of genetically engineered crops in the U.S. Updated July 1, 2009. Available at: http://www.ers.usda.gov/Data/BiotechCrops. Accessed March 7, 2010.

3. U.S. Department of Agriculture Economic Research Service. Adoption of genetically engineered crops in the U.S: Extent of adoption. Available at: http://www.ers.usda.gov/Data/BiotechCrops/adoption.htm. Updated July 1, 2009. Accessed March 7, 2010.

4. Monsanto Company. Conversations about plant biotechnology. Available at: http://www.monsanto.com/biotech-gmo/asp/default.asp

5. GM Watch. GM crops: Research documenting the limitations, risks, and alternatives. December 2009. Available at: http://www.gmwatch.eu/images/stories/gm-cropsgm-watch-version.pdf

6. Schneider KR, Schneider RG. Genetically modified food. University of Florida IFAS Extension. Pub. No. FSHN02-2. 2009. Available at: http://edis.ifas.ufl.edu/fs084. Accessed March 6, 2010.

7. Combating iron deficiency: Rice with six times more iron than polished rice kernels developed. Science Daily. July 22, 2009. Available at: http://www.sciencedaily.com/releases/2009/07/090721090129.htm. Accessed March 6, 2010.

8. Damude HG, Kinney AJ. Enhancing plant seed oils for human nutrition. Plant Physiol. 2008;147(3):962-968.

9. de Vendômois JS, Roullier F, Cellier D, Seralini GE. A comparison of the effects of three GM corn varieties on mammalian health. Int J Biol Sci. 2009;5(7):706-726.

10. Schmidt CW. Genetically modified foods: Breeding uncertainty. Environ Health Perspect. 2005;113(8):A526-533.

11. Mellon M, Rissler J. Environmental effects of genetically modified food crops — recent experiences. Union of Concerned Scientists. 2003. Available at: http://www.ucsusa.org/food_and_agriculture/science_and_impacts/
impacts_genetic_engineering/environmental-effects-of.html

12. Huppatz JL, Fitzgerald PA. Genetically modified food—safety and regulatory issues. Med J Aust. 2000;172(4):170-173.

13. Byrne P. Labeling of genetically engineered foods. Colorado State University Cooperative Extension Food and Nutrition Series. 2007. Available at: http://www.ext.colostate.edu/pubs/foodnut/09371.pdf. Accessed March 13, 2010.

14. Carter CA, Gruere CG. Mandatory labeling of genetically modified food: Does it really provide consumer choice? AgBio Forum. 2003;6(1&2):68-70.

15. World Health Organization. 20 questions on genetically modified (GM) foods. Available at: http://www.who.int/foodsafety/publications/biotech/20questions/en. Accessed March 7, 2010.