I had my sleeve October 2015, and my hair has thinned a lot. In fact, it's still falling out, but it has slowed considerably. My doctor and nutritionist have both assured me that it's normal and my hair will come back. I don't have bald Patches, but my hair is very thin. I think it's more noticeable to me than it is to everyone else.
I don't think it has anything to do with low Protein because I get more than enough protein every day, and the hair thinning still occurred.