well if you eat like a fat person you are going to be a fat person.
pretty simple.
but seriously. you will gain back 5-10 eventually just from having the weight of food in your system.
it is a reducing diet to lose fat/unhealthy tissue and clean up your bad eating habits.
if you go back to the bad eating habits that made you gain in the first place...well there is no diet/fast in the world that can keep your body from gaining weight.