Actually Blue Duck is correct. You really want to have zero fat/oil the day of the flush. Why? Because it triggers bile release. This, then becomes important because you have prematuraly released bile before you want to. The goal is to build up back pressure in the liver/gallbladder so when you trigger the release you have a blast of bile shooting through your duct to help carry out stones/ debris and toxins. To maximize the effect some people go with out fat/oil for a couple days leading up to the flush and load up on starches the morning of the flush. This helps build up even more back pressure for the main event. So, yes it is important not to blow your load prematurely due to oil/fat the day of the flush.