Pope Shenouda III
Can a person fast but at the same time not consecrate his fast to God?
Yes, they are many who fast, but God has no share in. For instance, someone may fast while far from God. He fasts, yet he does not change, still in weaknesses. A person of high profile or authority may even fast as a customary act, lest he should be embarrassed or for the sake of his reputation. Another may fast purely for bodily reasons, while the soul has no part in his fast.
One may fast to parade his ascetic ability or skill to abstain from food. A person may abstain from food for a while and at the same time indulging in wordily lusts which he cannot abstain from!