Why should what we eat have anything to do with God? Because we are not souls trapped in bodies, but whole persons, and the body prays with the soul. The Fathers see in food the very place of the first fall · Adam reached for what was forbidden and ate · so the fast is a small, daily undoing of that reaching, a relearning of obedience at the very table where it was lost.
This is not because food is evil; it is God's good gift, and the fast-free days and the feasts joyfully declare it so. We fast not because eating is bad, but because even good things must not be allowed to rule us · and because the body, disciplined a little, becomes a help to prayer rather than a weight upon it.