He that prays with fasting has his wings double, and lighter than the very winds. ... For nothing is mightier than a man who prays sincerely. ... But if your 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 you cannot fast, yet can avoid luxurious living.
-St. John Chrysostom, Homily 57 on Matthew 17,4,5. B#54, pp.355,356., 4th Century