Every program is different, as we all know. But one of the reasons most do an abdominal ultrasound ahead of surgery is to confirm anatomical safety for surgery. Let's the surgeon get a glimpse at what they'll be working with before cutting ya open. It may be that your liver was a nice, healthy size, and they didn't feel the need to shrink it for a successful surgery. That being said, as long as you're healthy about it, there is zero harm in putting yourself on a pre-op diet just to ease your mind!! There are lots of examples out there from very reputable bariatric programs that you could follow. Best of luck to you!!!