He that prays with fasting hath his wings double, and lighter than the very winds. ... For nothing is mightier than a man who prays sincerely. ... But if thy body be too weak to fast continually, still it is not too weak for prayer, nor without vigor for contempt of the belly. For although thou canst not fast, yet canst thou avoid luxurious living.
-St. John Chrysostom, Homily 57 on Matthew 17,4,5. B#54, pp.355,356., 4th Century