I am confused as the title of thread says "Do I need permission to fast," while your first post asks a different question: "Do I need to consult my priest about this?. I would echo other posters in recommending that you consult with your priest. However, fasting is one of those positive actions for which we do not need permission. Would you need permission top pray, give alms, be humble, loving and kind? That said, it is very important (indeed imperative IMHO) for you consult your priest on fasting for two reasons: (1) to enter into an Orthodox frame of mind wherein your priest as your spiritual father becomes part of your spiritual journey/family and (2) He can share the wisdom he has learned on this subject. It is not as cut and dry as it may seem. If you like, you can compare this to undertaking a diet and exercise regimen on your own or under the tutelage of a doctor or professional.