Hi Dawnie,
Welcome.
Having established the JO connection you may not need any further ammo. However, as far as I know, losing weight is a simple mathematical equation. You need to burn off more energy than you take in. So in those terms for someone who is pretty immobile due to pain therefore unable to move to burn off intake, you would have to live on grated carrot for every meal. NO WAY!
I am overweight too, and yes the OS did mention it, (every chance he had) but he didn't not do the operation. Even after the op he said, "now you'll get some weight off, won't you?" As he gently guided me out of his office. Well blow me down, because I have had my knee done, and am not in pain, I can actually move more and therefore can build up quad strength and drop a few kilos.
If you can do it before hand GREAT, but I would be pushing for an earlier review date.
PS. I was only just past 48 when I had my hip done, and only just past 49 for my knee, and now at 50 I feel like I'm 18 again!