If you want science then start with Wikipedias articles:
- https://en.wikipedia.org/wiki/Human_digestive_system
- https://en.wikipedia.org/wiki/Dietary_fiber
- https://en.m.wikipedia.org/wiki/Liquid_diet
And then read all the references when you want to dig deeper.
And add colours and levels for extra flavour.
They are diagnosed with Green Level 3 Wombleypoos, just keep them away from the level 2’s to avoid the floop scenario!