Fasting

“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.”

In context: Jesus says "when ye fast", assuming the practice, and directs it away from display.

“Then came to him the disciples of John, saying, Why do we and the Pharisees fast oft, but thy disciples fast not? And Jesus said unto them, Can the children of the bridechamber mourn, as long as the bridegroom is with them? but the days will come, when the bridegroom shall be taken from them, and then shall they fast.”

In context: Fasting is tied to seasons and occasions, not to a fixed calendar for everyone.