Without medical supervision of your body complications can happen on day one if you had a blood Sugar
issue. But generally things can happen within three days according to what I have read from pro-fasting alternative health doctors and what I know myself on carb needs to balance fluids in the body. They also suggest to keep Water Fast
to 10 days max.
I think it is safest to get a full check up before, during and after fasting. Plus you get to see results in the blood work! It cured my low iron problem.
If you are worried you could always mix your fasts for now to make it easier on the body. Try short juice or Water Fasts
with raw food. I do think that doing a long fast like that for your first or beginning fast is not good for the body. It has to do so much cleaning and can make you feel ill or be ill.
Everyone has thier own set of rules on how to take it. But above all, listen to your body. It knows better than anyone. If it keeps calling to you for food that could be a sign that you should work on clean eating first for awhile and then start your longer fasting journey.
My personal experience is that a week long fast feels perfect most of the time. Not too much and not too little. I like to follow up with a raw food diet after to continue the cleansing. Thats just how I prefer it. I think you could easily juice fast as long as you wish if you had the calories and nutrients to support you. I really do not like the super wired feeling I get after a week though. Isomnia!