My fiber experience is complex and has changed over the years. Cruciferous veg such as broccoli, Brussels sprouts, bell peppers, and cabbage, as well as legumes such as kidney beans and pinto beans, caused excessive gas and loose stools from childhood on. I eliminated them from time to time over the years and tried fiber supplements such as Metamucil. But powdered fiber supps seemed not to do anything for me.
Determined to find a way to keep these whole foods in my diet, I started eating them in small amounts on a daily basis, gradually increasing the amount. Over time, my body adjusted to them, and now I can eat a lots with very few side effects. Gas does happen but not to the degree it once did. And they no longer cause loose stools. I credit having gradually increased the amount and the kind of fiber.
So far, so good! I look forward to reading others' experiences with fiber. Hugs, Kim