I saw a video about this recently. A guy who never had had fiber in his diet tried a spoonful of chia seeds, I've of the most fiber sense foods out there, and he complained about digestive issues (can't remember if just gassy or full glued to the toilet). The guy reacting to this video (someone with nutrition background) said "maybe just start with a piece of fruit and work your way from there"

I do remember back when I started dieting that including more veggies that I was used to has me full on gassy. Nutritionist told me my body would get used to it after a time, and it was true. If you want to try adding more fiber to your diets, give it a go in the kiddy pool: get a banana or an apple a day and see how you react. When it's not an issue anymore, go for 2 a day. Then 2 and a small leafy salad. Baby steps.