My hair loss is not related to weight loss, but this info may help you just the same.
After my June 2007 hysterectomy, my hair started coming out in clumps. I now have all over thinning and a small bald patch in the back. Prior to my hysterectomy my hair was thick and in good condition.
During one of my post-op follow-ups with the OB-GYN surgeon, I told him and showed him my thinning hair and bald patch. He told me it was not uncommon after a long surgery (my surgery was 4 hrs) under general anesthesia to experience hair loss.
He told me that being under general anesthesia for a prolonged period can poison the hair follicles. The effect can take anywhere from 3 to 6 months before you start seeing excessive hair loss. Mine started approximately 6 months post-op.
Anyway, he told me to up my protein intake to at least 100 grams per day and to take a Biotin supplement at 1000 to 5000 mg per day.
I've been on increased protein and a 5000 mg daily Biotin supplement for a little over 2 months now. The excessive hair loss has now stopped, and I am beginning to get some re-growth.
Don't know if it would work in your situation, but increased protein and 5000 mg Biotin daily has worked for me.