Fasting runs through the whole of Scripture. Moses fasts on the mountain, David and the prophets fast in grief and supplication, the people fast on the Day of Atonement, and Jesus himself fasts forty days in the wilderness. He assumes his followers will do the same — 'when you fast,' he says, not 'if' — and the early Church fasted regularly, often on Wednesdays and Fridays and before great feasts.
The point of fasting is never the hunger itself. By voluntarily setting aside a good gift for a season, the believer turns the body's appetite into a prayer, sharpens attention on God, expresses repentance, and learns afresh that 'man does not live by bread alone.' It is almost always joined to prayer, and Scripture pairs it with almsgiving — what is not spent on oneself is given to the poor.
The forms vary widely across the Church. The Eastern Orthodox keep a demanding cycle of fasting seasons with detailed rules; the Catholic West observes lighter fasts and abstinence, especially in Lent; many Protestants practice fasting more occasionally and personally. The shared conviction is older than the variations: that the soul is sometimes fed by the body's hunger, and that learning to say no to oneself is part of learning to say yes to God.