My insurance requires 3 months of doctor and nutritionist monitored dieting before the surgery (6 months if I go with my own doctor, 3 if I go with the bariatric experts). So the first weigh in with them is considered my official start weight. I can lose as much as I want before the surgery, and it's still covered. I asked them to clarify again just to make sure I wasn't misunderstanding.
So maybe you should ask your doctor or even call the insurance company to see if you are in danger of losing too much weight to qualify for the surgery.
Kay