During this fast, we have to think of where God is and is not in our life. We will be substituting the bread of this world for the bread of life. We need to be conscious as we go through our days of what we want versus what we need. We will want to watch more tv, we will want to be on the computer, we will want to sleep. At each of these junctions, we need to turn from the things of this world and turn to God and his teachings. The fast is about focus, not success or failure when a fast is about success or failure, it becomes about us and not about God. Humility is important. If this becomes a matter of pride--"I WILL fast!" no matter what it costs in terms of how I treat others or becomes a source of self-congratulation rather than humble dependence, then the fast has become misguided and is no longer for the glory of God. At that point, you should focus on praying for and supporting the others on the fast, rather than continuing to fast in vain.
What a fast is and is not.
1 "Cry aloud; do not hold back; lift up your voice like a trumpet; declare to my people their transgression, to the house of Jacob their sins. 2 Yet they seek me daily and delight to know my ways as if they were a nation that did righteousness and did not forsake the judgment of their God; they ask of me righteous judgments; they delight to draw near to God. 3 'Why have we fasted, and you see it not? Why have we humbled ourselves, and you take no knowledge of it?' Behold, in the day of your fast you seek your own pleasure, and oppress all your workers. 4 Behold, you fast only to quarrel and to fight and to hit with a wicked fist. Fasting like yours this day will not make your voice to be heard on high. 5 Is such the fast that I choose, a day for a person to humble himself? Is it to bow down his head like a reed, and to spread sackcloth and ashes under him? Will you call this a fast, and a day acceptable to the Lord?
6 "Is not this the fast that I choose: to loose the bonds of wickedness, to undo the straps of the yoke, to let the oppressed go free, and to break every yoke? 7 Is it not to share your bread with the hungry and bring the homeless poor into your house; when you see the naked, to cover him, and not to hide yourself from your own flesh? 8 Then shall your light break forth like the dawn, and your healing shall spring up speedily; your righteousness shall go before you; the glory of the Lord shall be your rear guard. 9 Then you shall call, and the Lord will answer; you shall cry, and he will say, 'Here I am.' If you take away the yoke from your midst, the pointing of the finger, and speaking wickedness, 10 if you pour yourself out for the hungry and satisfy the desire of the afflicted, then shall your light rise in the darkness and your gloom be as the noonday. 11 And the Lord will guide you continually and satisfy your desire in scorched places and make your bones strong; and you shall be like a watered garden, like a spring of water, whose waters do not fail. 12 And your ancient ruins shall be rebuilt; you shall raise up the foundations of many generations; you shall be called the repairer of the breach, the restorer of streets to dwell in.