I went through a period in which I could easily double that and more. (about 220lbs)
Got rid of the wife, her clymer father, her quack social worker friends, and about the only thing now is non alcoholic beer.
I think it was described as a "maladaptive response to stress".
I think my friend will eventually experience what I like to call the "Dorian Gray Effect". He's in his early fifties; despite his monumental thirst he shows no outward signs of real damage from a consumption level that would have finished me off years earlier. I just know one day his whole system is just going to shut down all at once and he's going to age 20 years right before our eyes.
It's also a matter of genes in some people (think "Keith Richard") that they can keep up that level for years without it killing them.