What if you didn't eat anything? what if you fasted? How much weight could you actually lose?
A 200lb woman burns about 2400 calories a day with normal activity. If she could fast a week then she would only burn 16,800 calories or a little under 5 pounds. That's right, even if you could go without food for a week, you wouldn't even lose five pounds - you probably would be so hungry that you would gain it all back right away.
On a 1500 calorie diet, much more reasonable, she would burn 6300 calories for the week and could lose 1.8 pounds. Of course, as she loses weight, she burns less calories during the day.
Losing weight is a marathon, not a sprint! Pick a great diet, get your attitude on right and get started.