The general problem of fasting and extremely reduced intakes is that the metabolism slows down. Also you first lose a lot of muscles, then a bit of fat - when going on eating normal you burn less than before (because of less muscles) and therefore gain more fat. So for your body's composition I would say: Don't do it. (There is this great German book called "Die Physik des Abnehmens" = "the physics of weight loss" in which a physicist explains all this things very nicely)

However: I personally tried fasting for the mental effect, I was able to concentrate even better than normal, I liked the feeling of being "independent" from food and of being able to get through all of this things. (But I will not do it again because I try to get less body fat :) )