Just wondering...

This is my second time on MFP, last time though I did lose 60+ pounds, I also gained all those back.
I was eating too few calories, and excising....I would eat between 1000-700 calories a day, which I see a lot of people doing.
Then when I started to eat normal(1,200-1,600cal) all the weight just came back on.

I am just wondering for those of you who are eating only 700-1000 calories a day, aren't you worried what will happen when you start to eat normal? Have you had problems when you started to eat normal calorie amounts(1,200-1,600cal)? Can you really see yourself eating only 700-1000cal a day for the rest of your life? Because I couldn't.