In pursuit of health I tried 21 days of fasting (pure water fasting no juices or anything) It wont be fast enough and I think this is some kind of torture... depends on your current weight it can least weeks or even several months, in first 2-3 days you will have hunger because your body has glycogen stores (sugar in form of glycogen) and it takes up to 3 days for body to utilize it. Then you have fat stores, and when your body use fat in form of ketones as a fuel your hunger will be minimal, but there will be, I guarantee you.
The More you will fast the slower your storages will be consumend because body is really smart to keep you alive...it will slows down your metabolism rate and it wont use most of your proteins because thats most important for body. As your fat sorages will be smaller your hunger will also be raising (again) and after like 5-6 (even more) weeks I guarantee you that you will be tired of hunger,and even if your hunger will be small in that long period of time fasting even small hunger will be enough to make it stop.Later as your fat stores will be thining you will have more hunger eventually bigger than when you started. If you manage to fast this long Your body will start consume proteins, firstly muscles and your liver will decrease in volume and weight and now your hunger will be extremne, if you manage hold your fast then eventually your body will die because of eitiher lack of energy for your heart or some organ failure (kidneys, liver, lungs) Not a pleasant way to go, it is excruciating. But imho untill I was burning fat I felt good to be on fast, my mind was crystal clear, thinking was good, mood was good (actually best I could experience in life) but It was hard, its too long and not easy and last days will be painfull. You can try 7 days. In day 4-7 you can experience how you will feel like 70-80 % of time during fast. Even I on the 20 and 21 day of that fast felt big hunger and I still had enough fat stores (at least for another 21 days without protein burning) So Imagine that. But I actually support you to try it at least for 7 days or 10 (I do not recommend to be your first fast 21 days or longer you can actually die when you start eating again and it also wont be painless, quite opposite) because it has great benefit for your health, maybe it will help you with your health issues and you can gain will to life, as I said my mental clarity was super good during fast and even days after. But It can be permanent solution, I have completely different health problems and even fasting is not permanent solution for me. (genetics) Hope I helped, if you have question ask me , as long as I know or experienced I am gladly to help.