In general, any methods of discipline applied to the body which tend to modify its desires or repulsions, are good – for ascetic ends. But if done for display, they betray at once a man who keeps an eye on outward show; who has an ulterior purpose, and is looking for spectators to shout, “Oh what a great man!” This is why Apollonius so well said: “If you are bent upon a little private discipline, wait till you are choking with heat some day – then take a mouthful of cold water, and spit it out again, and tell no man!”
(C, The Golden Sayings of Epictetus, trans. by Hastings Crossley, 1909)
Study how to give as one that is sick: that thou mayest hereafter give as one that is whole. Fast; drink water only; abstain altogether from desire, that thou mayest hereafter conform thy desire to Reason.
Moreover when ye fast, be not, as the hypocrites, of a sad countenance: for they disfigure their faces, that they may appear unto men to fast. Verily I say unto you, They have their reward. But thou, when thou fastest, anoint thine head, and wash thy face; That thou appear not unto men to fast, but unto thy Father which is in secret: and thy Father, which seeth in secret, shall reward thee openly.