I've known top end actors who consumed 3.5-4.5 litres of vodka per day- think Liz Pena, John Cassavetes, Lee Remick, who were very skinny. When they put on weight they just liposuctioned it all out.

I encountered a lot of alcoholics through my work and I would estimate that 99% of them were skinny. They just don't look after themselves.

Advanced alcoholics often eat next to nothing, so the beer he was drinking may have been nearly the the total of his intake. I've known other serious alcoholics who were awfully skinny.