As an expression of lamentation and/or penitence, fasting nearly always is associated with weeping ( Judges 20:26 ; Esther 4:3 ; Psalm 69:10 ; Joel 2:12 ), confession ( 1 Sam 7:6 ; Dan 9:3 ), and the wearing of sackcloth ( 1 Kings 21:27 ; Neh 9:1 ; Esther 4:3 ; Psalm 69:10 ; Dan 9:3 ). In the New Testament Jesus chides the hypocritical Pharisees for disfiguring their faces when they fast ( Matt 6:16-18 ), a reference no doubt to the custom of smearing themselves with ashes. These objects and actions had no intrinsic penitential value but in a culture in which inner feelings were commonly displayed or even dramatized, when done sincerely they effectively communicated contrition. It became easy, however, for the outward exhibition of repentance to take the place of a genuine, inner attitude and thus become an act of hypocrisy.
Fasting is not a way to be forgiven of your sins, but rather a way to grow closer to God after he has already forgiven your sins. For your sins to be forgiven, cry out to God and ask him for forgiveness. Jesus (God) took the punishment for your sins - past present and future. Ask God to forgive you because of Jesus' sacrifice on the cross and realize you cannot save yourself by fasting or any other way. Only God can save you. Salvation is mercy. It is a free, undeserved gift of grace and love. Meditate on that and on the Bible. Read the book of John.
In a physiological context, fasting may refer to the metabolic status of a person who has not eaten overnight, or to the metabolic state achieved after complete digestion and absorption of a meal. Several metabolic adjustments occur during fasting. Some diagnostic tests are used to determine a fasting state. For example, a person is assumed to be fasting once 8–12 hours have elapsed since the last meal. Metabolic changes of the fasting state begin after absorption of a meal (typically 3–5 hours after eating).