How unhealthy is this?

Dumb dumb dumb. People will resort to such unhealthy ways to look thin. I can't even begin to explain the havoc he is wreaking on his whole endocrine system. I'd be surprised if his adrenal glands and insulin levels bounce back. Yes he'd feel weak, but he is masking that weakness with caffeine in the coffee which will stimulate his adrenal glands and serotonin enough to get through that crash, then he will self-medicate again. Once he stops this lifestyle, because no one can sustain that, he will have depleted his system of serotonin and will crash, with symptoms including lethargy, depression, anxiety, and a host of other physical responses. This is irresponsible to his well-being and he is taking for granted the proper care of his health.