40 days? That is insanity. Jesus prepped His flesh for its crucifixion. If any of us do it, it is self righteous. Not sure how anyone will beat me in a debate on that.
I fast for a day, then feel too self righteous and debate with myself for an hour, then eat like mad.
Fasting is good for health benefits. Spiritual too, if you feel God is not listening to your repentance from repetitive sin we battle with. But there are other means of putting the flesh under that are less disturbing to a self righteous radar / works based repentance. Like, helping out at an orphanage or paying an old age home a visit for a whole weekend. Anyone done that? What about a 40 evening commitment to the house handyman issues for the widows and elderly in church?