You should bare in mind that homebrew is not like shop beer - in that it contains vitamins. In moderation Homebrew is far better for you than the other stuff. Why not make weak beers and see how you get on with that.
I've actually lost weight since starting homebrewing, but I think that's because in that time I've also spent about an hour a day cycling. I also drink much less wine and spirits that I did a few years ago.