It is true just being depressed can cause weight gain, some of us get too tired or bummed for extra activity, we can tend to eat more (comfort food) and there have been studies that many depressed crave sweets (having many calories) not just feeling or looking at it as comfort food but eating these things actually produce "feel good" endorphins in our brains, unfortunately seems never enough to help the depressed brain without some intervention.
There ar others that lose weight while depressed, lose appetite. That had never been my "luck", mom, myself and her family (all having some mental disorder, mild) would opt for eating when depressed, and then just want to sleep constantly in between feedings.
Either way, we know depression sucks, I have noticed the longer a person (like my mother) doesn't seek out professional help, the more crippling it is for them, so the sooner a person seeks help the sooner they just may be on the road to remission/recovery.
I wish you all well, from the bottom of my heart

In giving advice seek to help, not please your friend
SOLON