Genetically modified organisms, or GMOs, are foods that have been chemically enhanced with the goal of improving the organism. Such methods have been used by companies like Monsanto on a variety of crops.

The majority of GMOs grown in the United States are referred to as "Roundup Ready," making it capable of surviving rounds of pesticides. Despite some perceived benefits, research has also linked GMOs to allergies, organ toxicity, and other health issues.

Mother Jones reports that genetically modified ingredients are contained in at least 70 percent of U.S.-processed foods sold in local supermarkets, though an exact count is difficult since companies aren't forced to inform consumers about GMOs.

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Here are the top six GMO crops grown in the U.S.:

1. Corn. Corn is the No. 1 crop grown in the U.S., with 12 billion bushels produced annually (from 2008-12) in primary states Iowa, Illinois, Indiana, Minnesota, Nebraska, and Ohio, according to Alberta Agriculture and Forestry's Agricultural Marketing Guide.

2. Cotton. According to the U.S. Dept. of Agriculture, 94 percent of cotton grown domestically is genetically enhanced. The seeds, extracted from cotton, are used for vegetable oil, margarine, or for frying foods such as potato chips.

3. Soy. A crucial element in processed foods, soy goes by several names, including hydrogenated oils, lecithin, and tocopherol, nearly 93 percent of soy is genetically modified, according to the USDA.

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4. Alfalfa. Dairy cows are often fed alfalfa, which is the country's fourth largest crop. The daily cows then provide many products, such as milk, butter, yogurt, and meat.

5. Papaya. Papayas are grown in many tropical climates, but that output is threatened by papaya ringspot virus (PRSV). A enhancement to fight off the virus was developed in the late 1980s, and the first resistant papayas were commercially grown in Hawaii in 1999. Chemically altered papayas now make up about 75 percent of the total Hawaiian papaya crop, according to GMO Compass.

6. Canola: An ingredient often used in cooking and biofuels, genetically modified canola accounts for about 90 percent of the U.S. crop. Canola altered to fend off the herbicide glufosinate or glyphosate has been available domestically since 1989, and unregulated since 1998 and 1999, respectively, according to Scientific American.

Special: GMO Foods: Are We Unknowingly Poisoning Our Families?

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Top 9 Foods Full of GMOs