One mistake is to make fasting just about eating or not eating literal food only .The true fast covers much more than which literally goes into a persons belly..
There is more than one level of understanding as the signified language of God . Parables as prophecy can be historically true and yet double to give the unseen spiritual application, the gospel hid.
Like with the disciples they could not cast out demons or the spirit of lies. The kind of lies that only can only come out with the gospel the power of God to loosen the grip of lying spirits. (prayer and fasting) Which is not just abstaining from eating food . Fasting in the bible is controlled or regulated eating a diet . Not eating never drove out one spirit of lies . It drives in hunger.
A good example in with John the Baptist in a parable found in Luke7.
There John was struggling knowing his end was coming. Having doubts as to whether Jesus was the one who represented the gospel . In a answer to prayer he sent for a answer which was followed by a series of metaphors that confirmed the gospel as a true fast. Which is again sharing one substance .
The gospel gives us the sight to see who were previous spiritually blind .Those who previously walked by sight as the spiritually lame are given the faith that comes from hearing the gospel to walk after the unseen. And other metaphors that represent salvation is given. The lepers to represent unbelief(unclean) are cleansed. Those dead in their trespasses and sins are raised to new spirit life, all of the needs of those poor as spiritually bankrupt are met in the gospel. To include covering the nakedness of those who know not the gospel as the righteousness of God, clothed with Christ .
The parable gave confidence to John so he could finish the work. The lying spirts that caused John to doubt were cast out. Many focus on the literal and it loses it gospel understanding
Luke 7:22 Then Jesus answering said unto them, Go your way, and tell John what things ye have seen and heard; how that the blind see, the lame walk, the lepers are cleansed, the deaf hear, the dead are raised, to the poor the gospel is preached.