Check with your doctor first with any precondition.
Juice Fasting is powerful and effective and may be a good approach. Some do a water fast with maple syrup and lemon (sometimes a dash of cayenne pepper for internal cleansing).
There is an entire approach to fasting you should consider. It should be for spirtual purposes and may become a sort of 'vision quest' (just using a popular term).
A Forty Hour fast may be a good introduction to the fasting path. Take your last meal at lunch on Friday, skipping Friday Dinner and all meals on Saturday, "Break-Fast" on Sunday AM gently with a light, vegetarian meal and plenty of liquids of your proper choice. You can do this each week for the month of December for example rather than a continuous four-day fast to begin with. Depending in where you live, summer fasting may be better for you, with higher outside temperatures to help maintain your body's core temperature (and thus demand for calories) for a longer term fast such as your proposed four-day.
Research and Study on your area of concern and interest before the fast. Prepare for the fast by doing a two-day vegetarian fast. During the fast, continue your research and study, in a very broad and still deep way. Meditate often on what you learn from your studies, thinking how it applies to others, the world situation, your particular situation. Read relevant scripture that applies to the results of your research and the area of your concerns.
Read up on "The Fasting Path" and do take reasonable precautions and preparations particularly with a pre-existing condition. Blood sugar levels can be properly maintained, and indeed, fasting and dietary changes can improve your condition significantly over time. Best wishes, let us know of your enlightenment experience!