urine will help prevent you from getting too hungry
that's the beauty of the UT
if you wish to supplement it with juices that is fine. Personally I have just done a pure UT fast before but bear in mind that you should make sure you do it while you have some time off work as your body will detoxify itself so you don't want to do anything too demanding or stressful to your body while you are doing this. Also make sure you get plenty of sleep. Doing a UT fast can leave you full of energy and sleeping may be difficult, sometimes mild sedatives are required to help you sleep. Remember the majority of all healing is done during the hours that you sleep.
Exercise is also important, go for 20-30 minute walks is a great way to get your lymphatic system moving and this helps speed up the process of elimination.