Passpost ???
If you can renew, I would just for piece of mind. You are only losing a couple of years of cost by doing it now and they are good for 10 years so it's only 20% lost. If not, maybe get a letter from your surgeon's office that states you had surgery and lost 100 pounds or whatever it is and keep it in your purse. They shouldn't give you too much guff at the border....unless you look like Osama Bin Laden or something. Faces don't change a whole bunch once you know it's weight lost. Your eyes don't move and your nose doesn't shrink. The letter would explain everything.
800 calories and less than 20 net carbs is the shizzle