That is the worst thing you can do.
500 calories will put you into starvation mode.
A female needs 1200 calories a day to survive, that is for organs to function correctly, regulate body heat etc, not even factoring in calories needed for movement. They say the average female needs 2000 calories a day for a reason you know!
If you eat less than 1200 your body thinks it is in danger of not surviving and therefore puts your metabolism into 'starvation mode' in which your metabolism decreases.
Eating 500 calories a day is just silly, not only from a health point of view but from a weight loss point of view because when you eventually eat normally again (and believe me, you will, nobody can live off 500 calories for the rest of their life!) you will just put all the weight back on and more.
If you want to loose weight properly, eat 1500 calories a day. You will loose about 1lb a week. It may seem slow but then when you go back to normal you will not put any weight back on, you will just stop loosing.
(PS: I assume you are a female, if you are a male 1200 becomes 1500 to survive, and 1500 becomes 2000 to loose weight)