Is it a mortal sin not to fast on required days?

[FuzzyBunny116]

I’m not talking about fasting before Communion, but during Lent and on whatever other days were are asked to fast, is it really a mortal sin to not fast? I always assumed it was just beneficial as opposed to necessary.

 

[Michelle_Arnold]

Recommended reading:

Annual Lent Fight by Jimmy Akin

(Note: Scroll to section titled “Penance in General.”)