"Because high amounts of fiber also tend to produce fermentation, high fiber foods are also eliminated. " This is so true. But it's so hard to break through the brainwashing of "high fiber = absolute good." I can dismiss that absolutism by pointing to the diverticulitis diet. Hmm, fiber is looking more suspect every day, no? I've learned that dal (often hulled, usually split pulses and lentils sold in bulk at Indian markets) does not irritate me, but unhulled lentils do. Soaking them does indeed improve digestibility, at least for me. So the "fiber" I have is coming from these small daring amounts of pulses and rice that I like to cook together.
Did you know that a slice of wheat bread was used at first to try and prove the FODMAP connection? But they realized it was a confounder because so many people have undiagnosed Celiac disease. If I have any amount of wheat, a knife of fire extends through the center of my neck up to my brain, and my bowels shut down, zero peristalsis for days. Yet some FODMAPS are ok in small doses for me. And as I recover, more FODMAPS are tolerable. So I'd cross reference the participants in that study and see if any of them turn up Celiac (they "grew out of" it maybe) or that triggers later.