200kcal/day is less than 10W. Since all energy the body uses is released as heat this puts the maximum sustainable heat radiation with such a diet at 10W. That

200kcal/day is less than 10W. Since all energy the body uses is released as heat this puts the maximum sustainable heat radiation with such a diet at 10W. That's about the level of a typical household LED, which at most feels slightly warm to the touch. At that energy level you could not sustain weight while maintaining body temperature let alone having a healthy metabolism. That's just a plain fact. You will lose weight long before you reach 200kcal/day.