I'm not sure, though I don't think that you can burn that much calories without excercising.
My wife has tried the same: some sorts of fasting, but did not have any success.
But she has told me about dietary supplements, which help you to burn calories before they metabolize into fat while reducing your appetite. The idea is to make your body produce more energy and to boost the blood heat, which would usually happen when you do exercises.
I don't know what to think about that. You know, I prefer doing excercises frequently, but I can understand those who say - like my wife - they don't have that much time and they don't enjoy going to the gym.