Its up to you. Fasting is not a religion its a personal experience and will to get your body healthy. If you want you can drink juice on a fast, tea or veg broth. I make some veg broth using tomato paste. However the more things that you add to your fast besides water the slower your body will detox (also the slower you will lose weight). This might be a very good thing if you have a lot of toxins in your body. The thing about Water Fasting is that you detox VERY fast and the effects of it might CAUSE you to go OFF the fast. If you add some juice or veg broth your detox will be slower but you still may feel detox effects. Its is solely up to you. You should experiment with what your body can handle.I no longer believe in suffering through detox, If it gets very bad have a bit or two of fruit or something and then continue to fast. Your body will still detox and you will still lose weight, Just maybe a tad slower for a couple days. A couple days isnt much in the scheme of things but it is when you are suffering.
By the way. I know someone who was doing a juice fast and lost a bit of weight over 10 days but not nearly as much as she thought she would. Turns out when we calculated the amount of calories in her juices it came to almost 1800 cals per day!
something to watch for if you are trying to lose weight!