When I teach on fasting and the changes its brought in my life, invariably someone points out Matt 6:1 "Be careful not to practice your righteousness in front of others to be seen by them. If you do, you will have no reward from your Father in heaven", and suggests that fasting must never be mentioned.
But I imagine when the Israelites in the Old Testament and Paul in the New Testament called large public fasts, they also taught on why the public fast was necessary. When we teach others about good things, it's not to look super spiritual, it's in hopes that they too can have the wonderful light of Christ in their life!
Matthew 6 talks in terms of fasting being something Jesus expects us to do. Check it out: 16“When you fast, do not look somber as the hypocrites do, for they disfigure their faces to show others they are fasting. Truly I tell you, they have received their reward in full. 17But when you fast, put oil on your head and wash your face, 18so that it will not be obvious to others that you are fasting, but only to your Father, who is unseen; and your Father, who sees what is done in secret, will reward you.
I believe it's good to discuss fasting with our spiritual circle of believers, to "spur each other on to acts of love and good deeds" Heb 10:24. Of course we don't wear an "I'M FASTING" t-shirt, or announce it as we walk through Walmart, but there is nothing wrong with sharing the experience with our Sunday school class or close friends.
Fasting is personal crucifixion of the flesh, guided by the Holy Spirits prompting. And sometimes that prompting comes from His servants!
Rom 10:14 How then shall they call on him in whom they have not believed? and how shall they believe in him of whom they have not heard? and how shall they hear without a preacher? 15And how shall they preach, except they be sent? as it is written, How beautiful are the feet of them that preach the gospel of peace, and bring glad tidings of good things!
James Disciple Johnson
Natl President and Founder
Disciple Christian Motorcycle Club