Jesus fasted for 40 days but it wasn`t 40 days of sitting around doing nothing. He was engaged in spiritual warfare as the enemy tried to keep him from stepping into his purpose and destiny:
Jesus, full of the Holy Spirit, left the Jordan and was led by the Spirit into the wilderness, where for forty days he was tempted[a] by the devil. He ate nothing during those days, and at the end of them he was hungry. (Luke 4:1-2)
I used to struggle with fasting, not able to get past 1 or 2 days. I found it hard, getting headaches, terrible stomach cramps, feeling weak and sick. I then noticed that on a busy day I could miss both breakfast and lunch and feel no ill effect. Yet, on a day of fast I would be overcome by hunger pains an hour after missing breakfast. What was this about?
A fast is not a matter of missing meals and it is most definitely not a diet. There is one purpose to a fast and that is to hear clearly from God, to get as close as we can to him, to have all the obstacles we have gathered to be removed so we can hear. It is not a time to skip meals but instead a time for some spiritual warfare, when we get onto our knees in prayer, entering into heart worship and diving deep into the Word. If we just create emptiness we are going to struggle but if we allow this time to become a lush garden of the Spirit then the fast will go quickly and will not end in failure.
If our fast is making us weaker and taking us further from God then we have a problem with our attitude and approach. It is better for us to stop, think it through and start at another time, understanding better our aims and goals in the fast. Perhaps we need to do more than fast food. Maybe we need to find a "desert", a place where we remove all the distractions from this time. Perhaps we should also fast our television, computer, books or whatever else is interfering with us seeking God's face.
Understand, if it's just about skipping meals we are not fasting, we are dieting.
When we emerge from our "desert" we should be stronger than we were when we went in. We should come out of it with passion and desire to see God's will complete in us and through us. We can't just go back to the same old same old. If we do then we know we did not really fast. You can't spend this kind of time with God and lay out this kind of sacrifice and come out the same. Jesus came out of the desert with the enemy under his feet, with his Father fixed before him and a passion to bring the Good News into the darkness. We should have that same experience, never to be the same again, ready to see the world changed by Jesus. If you come out this way then you know it has been a good fast.