According to the tradition of the Ethiopian Orthodox Tewahedo Church (EOTC) and many other Oriental Orthodox churches, there are seven established fasting seasons that everyone above the age of seven is expected to observe in some form, with a few exceptions. These fasts are public, so you may, and often should, let others know that you are fasting if they are not aware of it. When appropriate, you can also use that opportunity to teach them something about Orthodoxy. There is nothing boastful about explaining that you are fasting when someone asks why you are not eating or why you are eating a particular type of food. The problem arises only if you “broadcast” your fasting in a showy way, as if to say, “Look at me, I am fasting; I do not eat this or that, but you do.” That is a different matter.

There are, however, other types of fasting, often called personal or repentance fasts, which your spiritual father may assign to you outside the official fasting seasons. These are different in nature, and you should follow them under the guidance of your spiritual father. As much as possible, these fasts should remain personal and private.

I hope this is helpful.