Its not what you do, it is how you do it. Given my post yesterday regarding Ps. 51 and the necessity (or not) of sacrifices, this post from Middlebrow regarding fasting is apropos.
Biblical Fasting | The Scriptorium Daily: Middlebrow
As a result, what we have in fasting is a practice presupposed by the Bible but not directly established. “When you fast” –not if you fast, or “here’s an idea you never thought of: fast.” It’s a kind of biblical extra-biblical religious practice.
And then, to make matters weirder, the most detailed passages about fasting are negative, corrective, and even sarcastic. God’s best lecture on fasting comes in Isaiah 58:3-6 when the Israelites complain “Why have we fasted, and you see it not?” God responds, “Because you’re fasting wrong!”
It is not an overly long post and well worth reading.