To him it is sin
Others
The commandment of fasting is the first commandment given by the Lord to Adam when he told them not to eat from the forbidden tree. Fasting is a critical commandment of the Lord Jesus Christ for a complete and acceptable worship, and whoever does not fast with an acceptable excuse deserves a punishment.
Bishop Mataus, head of the Syrian monastery, said in his article about the fasting of the apostles and the Sacra