Blue Flower

Genetic engineering may pose health hazards to the human consumers of genetically modified food.

Genetic engineering is the process by which genes are altered and transferred artificially from one organism to another. Genes, which are made of DNA, contain the instructions according to which cells produce proteins; proteins in turn form the basis for most of a cell's functions. Genetic engineering makes it possible to mix genetic material between organisms that could never breed with each other. It allows people to take genes from one species, such as a flounder, and insert them into another species, such as a tomato -- thus, for example, creating a tomato that has some of the characteristics of a fish.

Starting in the 1980s and accelerating rapidly in the past decade, companies have begun using genetic engineering to insert foreign genes into many crops, including important foods such as corn and soybeans.[1] Just in the past few years, genetically engineered ingredients have begun appearing in many foods in U.S. supermarkets; they have been detected in processed foods such as infant formulas, drink mixes, and taco shells, to name a few examples.[2] These foods are not labeled, so consumers have no way to know when they are eating genetically engineered food. 

Genetic engineering is an extremely powerful technology whose mechanisms are not fully understood even by those who do the basic scientific work. In this series, we will review the main problems that have been identified with genetically engineered crops.[3]

Most genetically engineered crops planted worldwide are designed either to survive exposure to certain herbicides or to kill certain insects. Herbicide tolerant crops accounted for 71% of the acreage planted with genetically engineered crops in 1998 and 1999, and crops designed to kill insects (or designed both to kill insects AND to withstand herbicides) accounted for most of the remaining acreage. A small proportion (under 1%) of genetically engineered crops planted in 1998 and 1999 were designed to resist infection by certain viruses.[4]

Genetically engineered herbicide-tolerant crops are able to survive applications of herbicides that would ordinarily kill them. The U.S. food supply currently includes products made from genetically engineered herbicide-tolerant crops including "Roundup Ready" canola, corn, and soybeans which are engineered to withstand applications of Monsanto's Roundup (active ingredient, glyphosate), as well as crops engineered to survive exposure to other herbicides.[1]

Genetically engineered pest-resistant (or pesticidal) crops are toxic to insects that eat them. For example, corn can be engineered to kill the European corn borer, an insect in the order lepidoptera (the category that includes butterflies and moths). This is accomplished by adding genetic material derived from a soil bacterium, BACILLUS THURINGIENSIS (Bt), to the genetic code of the corn. BACILLUS THURINGIENSIS naturally produces a protein toxic to some insects, and organic farmers sometimes spray Bt on their crops as a natural pesticide. In genetically engineered "Bt corn," every cell of the corn plant produces the toxin ordinarily found only in the bacterium.

Unfortunately, genetically engineered crops can have adverse effects on human health and on ecosystems. And by failing to test or regulate genetically engineered crops adequately, the U.S. government has allowed corporations to introduce unfamiliar substances into our food supply without any systematic safety checks.

Here are some of the reasons why we might not want to eat
genetically engineered crops:

Ordinary, familiar foods can become allergenic through the addition of foreign genes.

Genetic engineering can introduce a known or unknown allergen into a food that previously did not contain it. For example, a soybean engineered to contain genes from a brazil nut was found to produce allergic reactions in blood serum of individuals with nut allergies. (See REHN #638.) Allergic reactions to nuts can be serious and even fatal. Researchers were able to identify the danger in this particular case because nut allergies are common and it was possible to conduct proper tests on blood serum from allergic individuals. In other cases, testing for allergenic potential can be much more difficult. When genetic engineering causes a familiar food to start producing a substance previously not present in the human food supply, it is impossible to know who may have an allergic reaction.

Genetic engineering has the potential to make ordinary, familiar foods become toxic.

In some cases, new characteristics introduced intentionally may create toxicity. The Bt toxin as it appears in the bacteria that produce it naturally is considered relatively safe for humans. In these bacteria, the toxin exists in a "protoxin" form, which becomes dangerous to insects only after it has been shortened, or "activated," in the insect's digestive system. In contrast, some genetically engineered Bt crops produce the toxin in its activated form, which previously only appeared inside the digestive systems of certain insects.[5] Humans have little experience with exposure to this form of the toxin. Furthermore, in the past humans have had no opportunity or reason to ingest any form of the Bt toxin in large quantities. When the Bt toxin is incorporated into our common foods, we are exposed each time we eat those foods.[6, pgs. 64-65.] And of course, a pesticide engineered into every cell of a food source cannot simply be washed off before a meal.

Toxicity can also result from characteristics introduced unintentionally. For example, a plant that ordinarily produces high amounts of a toxin in its leaves and low amounts in its fruit could unexpectedly begin to concentrate the toxin in its fruit after addition of a new gene. (See REHN #696.)

Unpleasant surprises of this sort can result from our ignorance about exactly how a foreign gene has been incorporated into the engineered cell. Foreign genes can be added to cells by various  methods; among other options, they can be blasted into cells using a "gene gun," or a virus or bacterium can be used to carry them into the target cells.[7] The "genetic engineer" who sets this process in motion does not actually control where the new genes end up in the genetic code of the target organism. The "engineer" essentially inserts the genes at a random, unknown location in the cell's existing DNA. These newly-inserted genes may sometimes end up in the middle of existing genetic instructions, and may disrupt those instructions.

A foreign gene could, for example, be inserted in the middle of  an existing gene that instructs a plant to shut off production of  a toxin in its fruit. The foreign gene could disrupt the functioning of this existing gene, causing the plant to produce abnormal levels of the toxin in its fruit. This phenomenon is known as "insertional mutagenesis" -- unpredictable changes resulting from the position in which a new gene is inserted.[8]  Genetic engineering can also introduce unexpected new toxicity in  food through a well-known phenomenon known as pleiotropy, in  which one gene affects multiple characteristics of an organism. (See REHN #685.)

Genetically engineered crops can indirectly promote the development of antibiotic resistance, making it difficult or impossible to treat common human diseases.

Whatever method is used to introduce foreign genes into a target
cell, it only works some of the time, so the "genetic engineer" needs a way to identify those cells that have successfully taken  up the foreign genes. One way to identify these cells is to attach a gene for antibiotic resistance to the gene intended for insertion. After attempting to introduce the foreign genes, the "engineer" can treat the mass of cells with an antibiotic. Only those cells that have incorporated the new genes survive, because they are now resistant to antibiotics.

From these surviving cells, a new plant is generated. Each cell of this plant contains the newly introduced genes, including the gene for antibiotic resistance. Once in the food chain, in some cases these genes could be taken up by and incorporated into the genetic material of bacteria living in human or animal digestive systems. A 1999 study published in APPLIED AND ENVIRONMENTAL MICROBIOLOGY found evidence supporting the view that bacteria in the human mouth could potentially take up antibiotic resistance genes released from food.[9] Antibiotic resistance among disease-causing bacteria is already a major threat to public health; due to the excessive use of antibiotics in medical treatment and in agriculture, we are losing the ability to treat life-threatening diseases such as pneumonia, tuberculosis, and salmonella.[10] (See REHN #402.) By putting antibiotic resistance genes into our food, we may be increasing the public health problem even further.

The British Medical Association, the leading association of doctors in Britain, urged an end to the use of antibiotic resistance genes in genetically engineered crops in a 1999  report. "There should be a ban on the use of antibiotic resistance marker genes in GM [genetically modified] food, as the risk to human health from antibiotic resistance developing in micro-organisms is one of the major public health threats that will be faced in the 21st Century. The risk that antibiotic resistance may be passed on to bacteria affecting human beings, through marker genes in the food chain, is one that cannot at present be ruled out," the Association said.[11]

To be continued.


Rachel Massey is a consultant to Environmental Research

[1] Union of Concerned Scientists, "Foods on the Market," available at Choose "biotechnology" in the
bar at the bottom of the screen, then click on "Foods on the Market."

[2] Consumers Union, "CONSUMER REPORTS: Genetically Engineered Foods in Your Shopping Cart," Press Release, August 23, 1999. Available at

[3] For one recent overview, see Environmental Media Services
(EMS), REPORTERS' GUIDE: GENETIC ENGINEERING IN AGRICULTURE, Edition 1 (October 2000), available from EMS, Washington, D.C., (202) 463-6670 or at Also see Pesticide Action Network North America (PANNA), "Genetically Engineered Crops and Foods: Online Presentation," available at

[4] Clive James, "Global Review of Commercialized Transgenic
Crops: 1999" ISAAA BRIEFS No. 12: Preview, produced by
International Service for the Acquisition of Agri-Biotech Applications (ISAAA). Available at

[5] See Michael Hansen, "Potential Environmental and Human Health Problems Associated with Genetically Engineered Food."
Presentation delivered at CREA International Seminar on Transgenic Products, Curitiba, Brazil, October 11, 1999. Available from Consumer Policy Institute, Yonkers, N.Y.:  914-378-2455.

[6] National Research Council, GENETICALLY MODIFIED
PEST-PROTECTED PLANTS: SCIENCE AND REGULATION (Washington, D.C.: National Academy of Sciences, 2000). ISBN 0309069300.

[7] Union of Concerned Scientists, "Fact Sheet: Genetic Engineering Techniques." Available at Choose "biotechnology" in the bar at the bottom of the screen, then click on "Genetic Engineering Techniques."

[8] See Food and Drug Administration, "Premarket Notice Concerning Bioengineered Foods," FEDERAL REGISTER Vol. 66, No. 12 (January 18, 2001), pg. 4710.

[9] Derry K. Mercer and others, "Fate of Free DNA and Transformation of the Oral Bacterium STREPTOCOCCUS GORDONII DL1 by Plasmid DNA in Human Saliva," APPLIED AND ENVIRONMENTAL MICROBIOLOGY Vol. 65, No. 1 (January 1999), pgs. 6-10.

[10] See World Health Organization (WHO), OVERCOMING ANTIMICROBIAL RESISTANCE (Geneva, Switzerland: World Health Organization, 2000). Available at

[11] British Medical Association Board of Science and Education, "The Impact of Genetic Modification on Agriculture, Food and Health -- An Interim Statement," May 1999. Summary statement available at