The liquid diet pre-op has nothing to do with insurance - it's designed to shrink the liver because most obese people have NASH (fatty liver), so it's less risky if the liver shrinks prior to surgery because the surgery involves lifting up the liver to get to the stomach. It also makes recovery easier. I did have a pre-op diet of low-carb, low-fat, high protein and lots of non-starchy vegetables, but again, this was my surgeon's requirement, not related to insurance. Insurance required me to attend 4 really dumb nutrition classes. I am very fortunate that my surgery covered it, but I personally think the entire US health insurance system is abhorrent.