Regarding cornflakes...this is what the author of IBS Free at Last says on her facebook page.
IBS-Free at Last also commented on their Wall post. IBS-Free at Last wrote: "I have never read the book Wheat Belly, so I can't really comment. As for wheat and FODMAPs and breakfast cereals. Original, plain Cheerios Brand in the US have wheat STARCH in them, which has the FODMAPs refined out of it so it is OK as a low FODMAP ingredient. Corn flakes is not a brand, so must check ingredients. For example, Erewhon corn flakes (Attune foods sends me samples) do not have any wheat ingredients in them. I just checked the Kellogg's site and their corn flake ingredients now look OK, too. But other brands might add wheat flour or high fructose corn syrup."