Getty Images About 20 years ago, a company now owned by Monsanto (MON) introduced the Flavr Savr tomato -- the first genetically modified organism approved for consumption in the United States. Since then, farmers across the country have been using more and more GMOs every year. It's a practice that has come under increasingly intense scrutiny. Activists who are worried about the potential for human health problems, as well as environmental damage, have started demanding that food containing GMOs be labeled as such. Prop 37, a California ballot measure to mandate GMO labeling, failed at the polls in 2012, and a similar measure lost last month in Washington state. In both campaigns, the largest makers of GMOs -- Monsanto, DuPont (DD), and Dow Chemical (DOW) -- provided the ad funding that helped turn the tide. But what many people don't realize is that they've been consuming products with GMO ingredients for years. The Institute for Responsible Technology has a brochure breaking down GMO presence in many different types of foods. Here are 10 of the most popular foods that likely contain GMOs. Pre-made soups can contain a large number of ingredients containing GMOs. For instance, Campbell's (CPB) popular condensed Tomato Soup lists high fructose corn syrup as its second biggest ingredient. According to the Non-GMO Project, nearly 88 percent of all corn planted in the United States is GMO.