My bf's crazy diet ... 😣

My bf wants to lose weight quickly... and he has gone onto a crazy dangerous diet and won't stop altho this could even make him die. He is not eating carbs and eating a lot of protein.... but it is not healthy. I am so worried, I've talked trough all the bad things it could happen to him and he just laughs, I'm just frustated and worried! What can I do to stop him? He needs to eat normal, and stop the extreme 😣