Genetically modified food refers to foodstuffs that have been produced from organisms where their genetic structure has been adjusted or altered from that which would occur naturally. Techniques to alter the genetic makeup of an animal or plant, or to transfer genetic sequence from one organism to another, have been developed and marketed since the last decade of the 20th century. Genetically-modified staple crops such as corn or soya have been available in much of the world since the early 21st century. Introducing the faming of genetically modified organisms (GMOs) and putting them on the mass market is a subject of controversy in many countries, because of fears it may lead to detrimental and potentially uncontrollable health and environmental effects.
Genetic modification of food crops is not confined to genetic engineering alone and is a subset of a continuingly developing field of biotechnology. The Food and Agriculture Organization (FAO) of the United Nations has a broad definition of agricultural biotechnology as "a range of tools that scientists employ to understand and manipulate the genetic make-up of organisms for use in the production or processing of agricultural products." This definition includes some traditional techniques such as the brewing and fermentation of beverages, as well as new laboratory applications such as genomic analysis, genetic marker-assisted selection, and the actual genetic engineering methods for direct manipulation of DNA. The FAO has a general positive attitude towards biotechnology as it notes a historic record and continued new opportunities for this study to aid agricultural practices and food security, especially in developing and poor regions.
With respect to direct gene modification, the FAO defines genetic engineering as transferring of a desired trait "found in an organism that is not sexually compatible with the host." This process typically involves transfer of genes through bacteria infecting the host plant, or the application of a mechanical device for inserting the desired gene called a "gene gun". The FAO differentiates three types of genetic transfers and the resultant genetically modified organisms. The first I called a "distant transfer," and involves gene transfer between organisms from two different kingdoms, such as animal, plant or bacteria. The second type is a "close transfer," where genes are transferred between two species within the same kingdom. The third type, known as "tweaking," is when the genes that are originally present in the organism are somehow rearranged to change the desired properties manifested through these genes' expression.
Genetically modified plants or animals that incorporate genes originally from other organisms are known as transgenic organisms. The FAO notes that most transgenic modifications occur for the purpose of "conferring insect resistance and/or herbicide tolerance." It is these properties as well as genetic modification-induced nutritional enhancement that have significant potential to raise yields and satisfy food needs in developing countries with growing populations. Criticism against the creation and production of genetically modified agricultural staples is centered on its potential to affect human health and the risk of uncontrolled genetic material dispersal and subsequent harm to naturally occurring species and ecosystems.
One concern expressed over health is the adverse allergic reaction or "allergenecity," of genetically modified crops. Researcher Dean Metcalfe writes on this subject in the compendium volume Genetically Modified Crops: Assessing Safety, edited by Keith Atherton. According to Metcalfe, adverse reactions such as gastroenteropathy and gastroenteritis have been associated with high protein foods, such as GMO soy protein. Other associated ailments include dermatitis and respiratory problems. While the cited research data on whether GMOs actually cause these problems is inconclusive, Metcalfe advises that the precautionary approach must be used, because of the potential adverse effects of developing allergic reactions.
Environmental effects are more difficult to discover and assess. In his book Genetically Modified Planet: Environmental Impacts of Genetically Engineered Plants author Neal Stewart outlines the main identified risks. One is that new pesticide-tolerant species may actually transfer their tolerance to neighboring weed species through various natural mechanisms. This would create what Stewart refers to as "superweeds," which are not susceptible to commonly used herbicides. Another risk involves similar contamination of valuable crop species including endangered local varieties by invasive GMO organisms through interbreeding. Stewart does not recommend the abandonment of genetically modified plant species altogether but advocates a cautious approach to experimentation. He is cautious about the "biosafety," of transgenic plant products as advertised by manufacturers because there may be adverse effects that take a longer time period to manifest.