Congratulations on your upcoming surgery. The one thing that was never mentioned was you can get gout during the fasting before surgery, and also after. I'd say that was worse than any pain I'd ever had.
After surgery, food tasted terrible. So for me, I could care less what other people were eating. The surgery also disrupts your hunger hormone. So, people that I know that had the surgery, just were not hungry.
Constpation was a problem for me, but it settled after a few months.
I wish you the very best on you upcoming surgery and for a smooth transition after.