I recently read a book written by a naturopathic doctor based out of North Vancouver, BC.
In his book, he clearly explains how our digestive system works, but most importantly, he shows how the food we eat affects our digestive organs and overall system.
If you have any illness or health issues, or you sincerely want to avoid getting sick, you should check out his book, Eating Alive, by Dr. Matsen.
Very informative and enlightening. He uses funny cartoons throughout the book too.