ABSTRACT: Genetically modified (GM) foods have been developed to resist herbicides or pesticides, to resist pests or viruses, and for other reasons. Large portions of common crops in the US are GM, such as sugar beets (95%), soybeans (93%), cotton including for cottonseed oil (93%), canola (93%), and corn and maize (86%). As with any new technology, all the risks associated with genetically modified organisms have almost certainly not yet been identified. Known risks include Allergic reactions, Antibiotic resistance, Toxicity, Decreased biodiversity, Undesired spreading, Resistant weeds and pests, and Poisoning wildlife. In addition, once GM genes are out in the environment, it is impossible to recall them. Furthermore, there is no way to assess, in advance, their full, long term impact and there is no monitoring system in place.
FULL POST: Genetically modified (GM) foods have been developed to resist herbicides or pesticides (so the herbicides can be used to kill weeds or the pesticides to kill pests without harming the desired crop), to resist pests or viruses, and for other reasons. Large portions of common crops in the US are GM, such as sugar beets (95%), soybeans (93%), cotton including for cottonseed oil (93%), canola (93%), and corn and maize (86%). 
The known risks of GM foods include those listed below. However, as with any new technology, all the risks associated with genetically modified organisms have almost certainly not yet been identified. Clear risk assessment procedures for known risks are not yet in place, let alone attempts to uncover and analyze currently unknown risks. Some of the risks, such as health issues such as cancer, are long term and possibly cumulative, so risk assessment is challenging. From a scientific perspective, this should put a substantial burden on those who wish to use the new technology to clearly demonstrate its benefits. 
- Allergic reactions: GM foods routinely contain new proteins, including ones that have never been in any food before. Proteins are the basis of most food allergies. Examples of GM foods where new proteins cause allergic reactions include soybeans with Brazil nut proteins (which trigger Brazil nut allergies) and vegetables with milk proteins (which trigger milk allergies).
- Antibiotic resistance: The genetic modification process often brings new genes that produce antibiotic resistance into a GM product. These can reduce the effectiveness of antibiotics in a person eating such a GM product and can also accelerate the development of antibiotic resistant diseases. Because of the widespread presence of antibiotic genes in GM foods, this impact needs to be analyzed cumulatively across the whole food supply.
- Toxicity: a) Some GM plants concentrate toxins (such as heavy metals like mercury) from the soil in the non-edible parts of the plant. However, there is a risk that toxins could also be concentrated in the edible part of the plant or that contamination of the edible part of the plant could occur. b) All organisms produce toxic substance to defend themselves against diseases and predators. GM foods could have increased levels of these toxins that could be harmful to humans.
- Decreased biodiversity: The push to use GM plants reduces the biodiversity of crops. The resulting monoculture of a single or a few varieties of a crop tends to require increased herbicide, pesticide, and fertilizer use, increasing costs for farmers and likely harm to the environment.
- Undesired spreading (specific examples below): GM plants (or animals) can spread in undesired ways. Notably, when insects pollinate GM plants they carry GM genes in the pollen they pick up and do not stay within prescribed boundaries. When they carry the pollen to non-GM plants, they can create seeds for undesired GM plants. This is a particular concern for organic farmers who do not want GM genes in their crops but whose fields are within the range of pollinating insects.
- Resistant weeds and pests: The herbicide or pesticide resistant genes in GM organisms or the changed usage patterns of herbicides and pesticides with GM crops may result in weeds, pests, and viruses that are resistant to current herbicides and pesticides. At least 10 species of herbicide resistant weeds have been identified.
- Poisoning wildlife: GM organisms may poison wildlife that feeds on them.
Examples of undesired spreading are well documented. Canada’s organic canola industry is basically extinct due to contamination from GM canola. In the US, in 2000, GM corn that represented only 1% of planted acreage contaminated at least 25% of the harvest that year. The GM corn was not approved for human consumption. The result was the recall of over 300 food products, export markets rejecting US corn, and corn prices plummeting for all US corn farmers. A class action suit against the GM corn creator, Aventis, led to a $112 million settlement for corn farmers. Corn farmers and users are concerned that a similar incident could occur with a new GM corn intended for biofuel production. 
In addition to the risks identified above, once GM genes are out in the environment, it is impossible to recall them. And because of the complexity of natural ecology, there is no way to assess, in advance, the full, long term impact of these genes. Moreover, there is no monitoring system in place to even look for such effects.
The next post will wrap up this discussion of GM foods by taking a look at what’s behind the lack of GM food labeling in the US.
 Wikipedia, retrieved 8/16/12, “Genetically modified food,” en.wikipedia.org/wiki/Genetically_modified_food
 Union of Concerned Scientists, retrieved 8/16/12, “Risks of genetic engineering,” http://www.ucsusa.org/food_and_agriculture/science_and_impacts/impacts_genetic_engineering
 Farm Aid, retrieved 8/16/12, “New GE crops on the market,” http://www.farmaid.org/site/apps/n1net/content2.aspx