A perhaps interesting note: beets themselves, cooked or not, are high FODMAP, which means they might cause digestive distress to sensitive individuals (you can only eat about 20 g). BUT fermented (or, rather, pickled) beets are quite okay in much larger quantities.

I also have an autoimmune (which is, according to many, always gut-related; diarrheic in my case as well :D ) and I'm combating it 'naturopathically' for years, with much improvement, but not a total remission. Fiber does help, especially in the 50-60 g per day range. Check out this, the meal plan will take care of possible nutrient deficiencies and is whopping in fiber amount.

I guess the older post you referred to is "How Plants and Food Gave Me Back My Life", so I'll check that out later.