How common is it to fast for 40+ days among Christians? I recently watched a testimony that reports the results of a 40-day water/juice fast (no food). The individual claims to have been addicted to drugs for 22 years, including marijuana, cocaine, mushrooms, LSD, ecstasy, prescription pain pills and alcohol. He went cold turkey, abstaining from both food and addictive substances during the 40-day fast, after which he reports complete freedom and no relapses.
I find this testimony quite impressive, both for the amazing results and the endurance required to accomplish such a long fast, but I also find it kind of extreme. I know that Jesus is reported to have fasted for 40 days too in Scripture, but to be honest, fasting for such a long period of time is not something you commonly hear about.
How common is it to fast for 40 or more days among Christians? What are the typical reasons Christians give for the decision to fast for 40+ days?
To his disciples, regarding fasting, Jesus says :

But thou, when thou fastest, anoint thine head, and wash thy face; That thou appear not unto men to fast, but unto thy Father which is in secret: and thy Father, which seeth in secret, shall reward thee openly. [Matthew 6:17,18 KJV]

So, regarding those who follow the words of Jesus, it would be impossible to say what they do or when they do it, for they do it secretly, unto the Father.