In terms of the quality of the food, there is no single way in which all genetically modified (GM) foods are different from all “regular” foods. GM foods can be modified in many different ways to achieve many different effects. The only constant difference between the two types of food is that GM foods have been manipulated through genetic engineering techniques while “regular” foods have not.
When we talk about GM foods, we talk about foods that are altered by more modern genetic engineering means. These foods are altered in the laboratory, not through cross-breeding. This makes it possible to do things like combining genes from entirely different plants and species rather than just cross-breeding members of the same species.
This experimental technology merges DNA from different species, creating unstable combinations of plant, animal, bacterial and viral genes that cannot occur in nature or in traditional crossbreeding. Virtually all commercial GMOs are engineered to withstand direct applicatio ... and/or to produce an insecticide.
This is not to say that all “regular” foods are just the way nature made them. In fact, essentially none are. All of the food we eat has been genetically modified over millennia of selection by farmers. People have selected and bred plants that have the characteristics that they want. In this sense, they have been genetically modifying plants (and animals) for thousands of years.
Using these techniques, scientists can create GM foods that differ from “regular” foods in many ways. Some may have different food qualities like more protein or “better” fats. Others may simply be easier to raise because they are more resistant to disease or pests. The actual differences between the foods can vary. The only consistent difference is that GM foods have been genetically engineered.