Mike, I found that statement puzzling also. The only thing I can think of is that the author may have gotten this part backwards.
Can calcitriol cause weight gain? - Calcitriol Questions - Ask a Pharmacist on Everyday Health - EverydayHealth.com
"According to the package insert, loss of appetite and weight loss are side effects of calcitriol, but not weight gain."
I think the confusion stems from there being a controversy/misunderstanding surrounding calcitriol.