I did back to back 7 day water fasts about a year ago. By the end a general sense of well being was washed over with waves of euphoria, optimism, and gratitude for merely existing. It was like a layer of grime had been wiped off my windows to life. I’m convinced the brain operates better on ketones. Your mileage may vary.
There is 0 spiritual benefits unless that’s what you are looking for. Just like a damp cave that would make somebody uncomfortable while an ascetic monk may find it amazingly cozy.
Having said that there is a quiet place you can find when your body stops making all sorts of hormonal noises and your stomach is empty. It is a great place for contemplation.
It may make you feel light-headed and less prone to logic, so there’s a good chance it’ll enhance your feelings of spiritual growth.
As unlucky clock said, if you’re looking for a spiritual experience, there’s a decent chance you’ll get one.
1 Dear friends, do not believe every spirit, but test the spirits to see whether they are from God, because many false prophets have gone out into the world. 2 This is how you can recognize the Spirit of God: Every spirit that acknowledges that Jesus Christ has come in the flesh is from God, 3 but every spirit that does not acknowledge Jesus is not from God. This is the spirit of the antichrist, which you have heard is coming and even now is already in the world.