starvation mode???

ok, i keep seeing posts about how there is no such thing as starvation mode and by eating 1200 calories a day PLUS exercise calories, you are actually hindering your weight loss. i know there is information on this on the website and i have heard it explained but some one please help me understand? this morning i was feeling good about my progress and then i read a horrible blog by this woman that only eats 600 calories a day and to me looks so sick and malnutrtioned. she said something about the people on the biggest loser working out for 6-8 hrs a day and never eating back those calories, so why should we? does anyone else want some answers???