In the New Testament Jesus does not explicitly say that we must fast but His words and actions imply that we must lol. So what does He say? In Matthew 6:16-18 Jesus says "When you fast, do not look gloomy like hypocrites, for they disfigure their faces that their fasting may be seen by others. Truly, I say to you, they have received their reward. But when you fast, anoint your head and wash your face, that your fasting may not be seen by others but by your Father who is in secret. And your Father who sees in secret will reward you." So the first major thing to point out here is that Jesus says "when you" not "if you". He is giving instructions on how fasting should be done when you do so because you are most certainly going to do so. Also, Jesus is specifically letting us know that fasting isn't a trend or something we do to impress others like my friend was stating society has made it, but rather that it is to be strictly between us and God. We are not to brag and boast about fasting and we should actually keep it to ourselves as much as we can.