As an act of faith, trust Him to empower you. Although fasting is primarily a spiritual discipline, it begins in the physical realm. You should not fast without specific physical preparation. If you plan on fasting for several days, you will find it helpful to begin by eating smaller meals before you abstain altogether. Cutting down on your meals a few days before you begin the fast will signal your mind, stomach, and appetite that less food is acceptable.
Some health professionals suggest eating only raw foods for two days before starting a fast.
I also recommend weaning yourself off caffeine and sugar products to ease your initial hunger or discomfort at the early stages of your fast. 1997 Campus Crusade for Christ .