Yes you can. Manuel Uribe, former heaviest person on earth lost 400kg. He now weights 200kg.
Heaviest person in history lost 420kg and was at 215kg but went back to 430kg after they released him from hospital where he was on the strict diet (I'm currently on the same 1200 calories per day, proteine diet).
One dude lost more than 200kg and became fitness trainer.
Major problem is excess skin, if you lose a lot of weight too fast.