In short, it can safely be said that consuming 500 calories a day is not healthy. You may be obsessed with the calorie count and fat content and carbohydrate content of everything you are eating, but it is not going to help if you don't know how to combine these figures to make yourself a healthy meal. You can start suffering from anorexia, an eating disorder, and it can lead to severe health effects, all of which you were trying to ward off by losing weight.