We don't have GMO Corn in my country and it's still hard to digest.. That's just the nature of corn I'm afraid. I'm quite sure everyone with a leaky gut or hypersensitivity has built up enough problems that they will probably never fully recover to the point of being able to eat everything a more hardy person can. I was getting pretty over eating almost nothing and weighed only 55kg last year. Now I just take my mast cell stabilisers and antihistamines and get on with my life. So long as I take the mast cell stabiliser I can eat anything without any gut issues at all and my digestion is now perfect (and I've gained 11 kg over the last year). I figure at some point my gut will get thick enough that I can cure myself with weight gain lol. Life's much easier when you can eat Chocolate without getting sick
I still don't eat grains other than Rice but I could if I wanted to, well everything other than Gluten containing grains would be OK.