I believe fasting is about 2 things (1) Its about denying self. Willard says "fasting is one of the more important ways of practicing that self-denial required of everyone who would follow Christ." If your doing a fast from food of more than a day, you will need to be prepared to battle the flesh minute by minute. Its not the hunger so much as its the mind telling us we have to eat, this is not normal, stop doing this! I fast to send a clear message my own self and my own will that the spirit man is the one who is in control. My life is devoted to Jesus Christ in every sense and reality. He is the Lord over every aspect of my life and the body will not get food until self takes its rightful place as servant to the call to follow Christ. If we don't learn to suppress self, it will grow stronger and breaking its hold on our lives will become more and more difficult.
(2) Its about seeking the Lord. Fasting will empty you. As you feel the hunger come and go, you feel the discipline of remaining in an empty space grow stronger. You feel the space for Christ in your heart and mind expanding. The very real pains of fasting will focus our minds on the Lord. Meal times become prayer times. I remember having some of the best prayer walks during lunch time when I've fasted in the past.
Fasting does not need to be only about food, but I think we should not loose the connection between fasting and food. Some people will fast TV, or entertainment, or social media. During one of my weeks on campus at Regent, I decided to fast by eating simple food for meals, no snacks or anything between meals, and no TV or entertainment of any kind. I was able to spend a great deal of time focusing on what the Lord wanted to speak to me that week. Another time, I was struggling to deal with mounting frustrations in my life. I desperately needed answers from the Lord, but they would not come. I remember telling God I was desperate and He said "No your not." He was right of course. What I really wanted was to get answers without dying to self. I decided to fast eating only one meal a day until I got some answers from God. I felt a little like a toddler throwing a tantrum, but God allowed me to do this. After three weeks, I found I was drawing closer to God and enjoying my times of prayer with him so much that I forgot all about getting answers. Then one day I realized the answers I needed were there.
Fasting is about obedience and the Lordship of Jesus Christ. This is a discipline that all disciples need to engage in at some level. Use wisdom, start out slow, and allow the Holy Spirit to guide you.