Water only fasting is the best way to ensure you’re maximizing autophagy (cellular repair) and the benefits of fasting. There are a few important things to know before you dive in:
(1) If you're on blood pressure or diabetes related medications you may need to adjust them as a result of extended fasting. What often happens is that fasting works so well you often need less medication -- so it is always a good idea to check-in with a medical professional if you're on meds in particular before you spend too much time in a fasted state.
(2) With fasts lasting more than 48 hours, you may need to supplement potassium, sodium, and magnesium or other electrolytes. Taking about a teaspoon of salt each day can help as can electrolyte powders developed for fasting or replenishing electrolytes post-exercise.
3) Set your environment up for success -- you're going to want to get rid of all tempting food. This means throwing it out or giving it away before you start. You’ll be amazed at how much easier fasting is when you get the temptations at least a car ride away.
(4) Pick days/times where you're busy, but not particularly stressed. You want to fast after having a good night sleep and on a day where you’re not overly stressed with work or family obligations. Set yourself up for success, especially in the beginning!
(5) Have a clear intention for the fast (to achieve a particular goal, to get clarity on a life situation, to enhance a prayer, etc.) Writing this down before you begin can help provide the motivation you need to get through the tough bits and you will be amazed by the mental clarity you begin to have particularly after the 36 hour mark.