Oil is fat, when fat ingested, the gallbladder has contractions to excrete more bile to handle the fat.
If the gallbladdercontracts when you put fat in body, it is a sign of a well functioning gallbladder. If the gallbladder does not contract and excrete more bile it is a sign of a diseased gallbladder.
As a result of the oil (fat), more bile salts are excreted into the small intestine to try to break down the fat. As the green bile salts are entrapped in the fat, it continues to pick up calcium and other minerals, including cholesterol in the intestines.
There is no denying it makes many people feel better. So did the old castor oil in orange juice, but it still tasted nasty :-p
Why do you feel better afterward?
My guess is, it is also bonding and cleaning the cholesterol. calcium and other minerals, metals and other impurities gunked on the intestinal walls and flora, and also relieves congestion in your intestinal system, and lets your flora start releasing vitamin b-6 again. Giving you a cleaner start.
When you work in chemistry, you notice acid ( citric acid s?) is used to form reactions break down some solids, salts (bile salts?) are used as a catalyst to bond the molecules in the slurry to form a different molecular solid.