First.. why would you eat only 1k calories a day? :smashfreak8:
Second.. If I was in your situation I would start off with a protein/fat type diet and add carbs in only around my workout
Honestly though with such a drastic jump back and forth I dont know how your body will respond. It may see the food and since you have been under eating it may see it as a chance to store it for energy later (fat gain).
Start off slow and dont jump in too much at once. Start introducing extra calories slowly and limit carbs to only around workouts.