a mamin, I do not believe that it is healthy for a person to eat 700 calories per day for any length of time. This will put the body into what is called “starvation mode”. The body thinks you are planning to starve it and therefore refuses to convert fat stores to process them out of the body. Instead it steadfastly preserves those fat stores since it truly believes it is starving.
I strongly recommend a well-balanced diet with portion control and limiting either sugar or fat intake (whichever seems to be a bigger issue for you). I have somehow managed to lose a few kilos in the last several weeks just trying this basic idea, even though I lead a very sedentary lifestyle. Also, drink plenty of fluids and get enough rest, as the fat is processed out during sleep and the fluids will keep your skin elastic while it is shrinking.
Hatzlacha!!!