I no chiropractor, but I know that the nerves from the spine go to all parts of the body enabling movement and nourishment of those areas with good blood supply. If you have subluxations and misalignments in your body certain organs and areas of the body can be adversely effected. An obvious example is a lower back problem causing sciatic leg pain. Chiros are usually very knowledgable about the body, not just bones and nerves, and can identify areas that need strengthening and help the body to be able to help itself.
The diff between psyllium and high fibre cereal??? Psyllium is the husk of a variety of plantain and is an excellent mucilaginous fibre. High fibre cereal could be any mix of whole grains and brans maybe, but it can't really be compared in action to psyllium which provides no nutrition, but excellent bulk for those who can handle it.