Jill,
My understanding of how the process works is that with nothing but liquids, after about three days, your body's digestive system goes into a hibernation/cleaning mode and any fiber you take in will quickly switch it out of that much desired state of cleansing and plop you right back into what is termed 'starvation mode'. I would try to stick it out with no food and if you find you can not do so, go ahead and break the fast for a few days and start again when you are ready.
On day 5 here and dreamed about a bowl of raisin bran crunch cereal - and am so fighting that tempation!