what is your current weight? there are calorie calculators all over the net that will give you an approximate number of calories to maintain your current weight -- 1200 - even if you are a total couch potato is very very low... Not that I would question a member of the medical profession, but i think your doc is a little mistaken.. or perhaps suggested that you go on a 1200 calorie diet... 700 calories a day, unless it's medically supervised is dangerous...
There is a woman in this forum who is doing around 800 calories a day, and I am spacing on her name, but she is under medical supervision while doing it.. Doing it that low on your own you are correct to question.