This is getting out of control. Not you, not the friend you want to get in shape with, just the whole fitness community.
Losing weight is not only dependant on how much calories you insert in your body (consuming more that you assimilate is surely THE factor that makes you lose weight, don’t get me wrong on that), but it is EXTREMELY dependant on the person itself. The 500 calorie diet might work for your friend but it could drastically damage your organism, just because metabolism works differently from person to person. The VLCDs are only for fat loss and not for muscle gains, and I always suggest to do both.
Just to be a bit more scientific: a 500-calorie diet is an extreme form of a very low-calorie diet (VLCD). It requires you to drastically reduce the amount of food you eat, usually to a maximum of 800 calories per day.
I’m not sure I understand the question. 500 cal per day during a week? If so, my advice is DON’T TRY! Why would you even want to torture your body in such way? It’s dangerous and it is not recommended! Let’s say you’re stubborn and you will try this draconic diet. What would happen next? Do you think you’ll shed 10 kilos just like that? Do you think you’ll be able to get back to normal eating and not regain the kilos you have lost and even some extra? Not to mention 70% of all this weight you will lose is WATER. It doesn’t mean anything.
Eat smart!! Choose smart!
You will damage your metabolism if you do so. 500 calories is very less. Check your BMR from any health centres. Start your diet with your BMR, for example, if your BMR is 1400 start with 1400 calories and keep increasing 100 calories every week till you reach TDEE. Never go less than BMR. Good Luck.