It has been said in the dilution sticky (at the top of the page) that having a high fiber diet will help a week or so before the test, but in the last 3 days before the test it is good to load up on fatty foods and to keep excersizing to a minimum. Again this is all coming from the mindset that you'll be taking a lab or probation test. But still I think fiber is only beneficial if you do it 4 or more days before the test