Hi Scorpioeyes,
I used to be very serious about bodybuilding and in the past I had a partner who would start any weight gaining program with fast of 5-7 days (two times a year). He would get his weight back very fast and I couldn't believe how much better defined he would become than before the fast. Although to recover strength usually took him much longer. Another interesting thing was that he would increase his measurements (biceps, chest...) without actually increasing his weight.