GMO foods have been studied in an exhaustive manner, and they will continue to be. All of us in the US have been eating GMO foods for a long time. They have been around, legally, since 1994, when the Flavr Savr tomato was approved by the FDA for marketing. The modification allowed the tomato to delay ripening after picking.
With a little help from Wiki: In 1995, the following transgenic crops received marketing approval: canola with modified oil composition, cotton resistant to the herbicide bromoxynil, Bt cotton (Monsanto), Bt potatoes (Monsanto), glyphosate-tolerant soybeans herbicide (Monsanto), virus-resistant squash (Monsanto-Asgrow), and additional delayed ripening tomatoes (DNAP, Zeneca/Peto, and Monsanto).
In 2000, with the creation of golden rice, scientists genetically modified food to increase its nutrient value for the first time. As of 2011, the US is the leading country in the production of GM foods. Twenty-five GM crops had received regulatory approval. As of 2013, roughly 85% of corn, 91% of soybeans, and 88% of cotton produced in the US are genetically modified.