F 28/5'4/100 lbs
"I'm not a psychopath, I'm a high-functioning sociopath; do your research."
Look for foods high in inulin fiber.
Inulin - Wikipedia, the free encyclopedia
Although keep in mind that most prebiotics, though they will cause the proliferation of good gut bacteria also nourishes the bad. So if you're currently having gut issues, it might be good to lay off for a bit and stick to repopulating the good gut bacterias with some high quality fermented foods.
Also, foods high in Resistant Starch, green-ish bananas, potatoes, plantains