Quoted from Dr. John McDougall: Excreted cholesterol enters the gallbladder and thereby contributes to the production of gallstones. (90% of Gallstones are made of cholesterol) Excessive amounts of cholesterol in the lower intestines are believed to be involved in the development of colon cancer. Vegetable oils will cause cholesterol to be eliminated from the body , lowering our risk of heart disease. Unfortunately, however, because this cholesterol is excreted through the gallbladder and into the colon, your risks of developing gallbladder disease and colon cancer are increased the more cholesterol you excrete. Thus, a change to a no-cholesterol diet is not only the most effective, but the safest way to lower your cholesterol level.
My comment: This must be why the olive oil flushes out the stones, because he states vegetable oils will cause cholesterol to be eliminated from the body.