Libby - By keeping your calories very low for too long can actually slow your metabolism. Your body adjusts to the new calorie level by being able to function on only 800 calories. This could potentially backfire when you up your calories to a more practical level. Have you thought about calorie cycling instead? I don't want to post any links here...I think they would be removed? Google calorie cycling or zig zagging calories and have a read and see what you think. I personally think it could be just as effective and easier to sustain for a longer term...if not forever really.
"WARNING: Exercise has been known to cause good health and happiness"