I've never heard of this 500 calorie a day diet and my first thought was that those people must be starving constantly. Looking at the link, I can tell you that, even without the additional research, there is no way I would believe that is healthy. Your body tells you that you're hungry because it needs nutrients; taking away that hunger is taking away the warning system. It is much better to eat something when you're hungry--just make it something small and healthy, and eat slowly so that your body has time to recognize that it's been fed and you don't think you need more food.