One aspect of the psychology of fasting is the issue of CONTROL.
In the most aberrant forms of fasting it is the psychology of being out of control, distorted self-image and depression which impels the act of will beyond any measure of moderation. Naturally, we would not longer call it "fasting" so much as "starvation".
The idea that "holy" people fast is certainly alluring to the frame of mind of already distorted psychologies. Jesus is said to have been a human and fasted for 40 days. If this isn't ridiculous I don't know what is; unless the fasting were merely relinquishing one particular part of one's diet.
I use to work with a Koren Christian who was trying to fast and pray like a friend of his who fasted for 13 days until he was, quote: "So holy he could speak directly to god and levitate at will."
Uh huh. Right. See what I mean?
Hare Krishna devotees are kept without protein in their diet to make them fuzzy-minded enough to be controlled by their group leader. They are put out into the city and told not to come back until the collect X amount of money from donations.
Read MONKEY ON A STICK.
I'm not saying, of course, that all people who fast are nutjobs. I am saying that it begins to demonstrate that their is an out-of-balance condition of the mind when the reasons given for the fast stray into the Twilight Zone.