Your body will adjust to a new diet in about a week if you went on a vegan type fast(fresh veggies and fruits only), to trick your body. Then when you do the flush, your body will get a huge suprise from all the fat from the oil.
Or you could take it slower, and do a low fat diet for two or three weeks, (when I say low fat I mean clean low fat, no "low fat/high sugar" foods) and then attempt it.