Corn used for food has been genetically modified to tolerate various herbicides and to express a protein from Bacillus thuringiensis (Bt) that kills certain insects. About 90% of the corn grown in the U.S. was genetically modified in 2010.ost food modifications have primarily focused on cash crops in high demand by farmers such as soybean, corn, canola, and cotton seed oil. These have been engineered for resistance to pathogens and herbicides and for better nutrient profiles.