I encountered the broth concept while looking at the GAPS diet. But there are tons of references, just google broth + villi, or bone broth + leaky gut, etc. Some favor the bone for the minerals, others vegetable/potato broth. It's all from the alternative community, so it's not like a double blind study or anything, so no proof. But I think it's all good, and works pretty well (for me).
Medical fasting, aka Therapeutic fasting, or Water Fasting does have a bevy of scientific support. I'll load you up with some links.