I’ve never been told the fasting is to prevent post-surgery vomiting. It’s so you don’t aspirate and choke during surgery. At least that’s what I’ve been told for decades and several surgeries.
Post-surgery, if you’re a post-surgery puker, which I am, you’re gonna retch whether there’s food or not. (They can deal with that now, with drugs.)
Bingo!
Here is truth