On acceptable fasting

Fasting is acceptable to God when abstention from food is accompanied by refraining from sins--from envy, from hatred, from calumny, from vainglory, from wordiness, from other evils.  He who is fasting the true fast that is agreeable to God ought to shun all these things with all his strength and zeal, and remain impregnable and unshakeable against all the attacks of the evil one that are planned from that quarter.  On the other hand, he who practices abstention from food, but does not keep self-control in the face of the aforesaid passions, is like unto one who lays down splendid foundations for a house, yet takes serpents and scorpions and vipers as fellow-dwellers therein.  St. Photios the Great