Humans have been eating wheat and corn for thousands of years with no problem. It's only been since the arrival of GMO grains that people have trouble digesting it. That's because the structure of the grains has changed and humans haven't developed the enzymes needed to digest them. What happens when the body can't digest something? It causes inflammation and ends up being stored as fat, which is why suddenly obesity is a problem even for people that don't eat a lot.