I didn't bother reading the rest of what everyone else wrote I just want to tell you what I know.
When you starve yourself your body goes into survival mode because it thinks you're starving. When your body goes into survival mode your metabolism slows down as well, in order to preserve the energy supplies it needs in order to survive.
Regardless of how little you eat and how much you exercise your metabolism will not get any faster because it still knows that it needs to preserve what nutrients you are taking in.
When you start to eat regularly again your body will remain in this survival mode until it realizes that it is receiving nutrients on a regular basis, as it sees fit, so you're pretty much gauranteed to gain weight back during this period. Remember - your body thought it was starving and is now preparing for future times of starvation.
It takes time for your body to recognize that your metabolism can speed up. So, yes you're pretty much guaranteed to gain weight at the end of your restriction period.