You have identified Debra’s fasting during the month of Ramadan as a matter of religious doctrine, enforced by personal faith.
Fasting during the month of Ramadan is something dictated by the rules of Islamic faith. On the facts given in the example, Debra behaves in accordance with those rules because of her religious beliefs. There can be other reasons for fasting (for example, in support of charitable fund-raising) but that is not the case here.