Definitely BEFORE. You will never look at a cruise the same way again after surgery! I will still cruise, but my next one will be a very different experience than any of my others since I can eat so little now.
Keep in mind that they also overload you with fluids in the OR to help prevent nausea; the fluids add a lot of weight until your kidneys kick in and you pee it all out. The weight loss WILL come. Try to be patient and take good care of yourself. Be proud you just did something AWESOME for yourself!