From what I've read, each surgeon/program has their own preferences for pre-op diets and the results vary pretty widely. The primary goals are 1) to prove ability to adhere to a diet (this is mostly an insurance thing, I think) and 2) to shrink the liver, but even if the liver remains relatively fatty, the surgery can still be conducted. It generally requires an additional incision to allow for direct liver retraction and can make the surgery time longer, but its not impossible. That being said, I would say if you have researched your surgeon and are confident in their skills/success rate, then you have no reason to doubt their pre-op diet recommendations. Its very likely that they are moving you towards a low carb, reduced calorie diet, even with the inclusion of some fatty/carby foods. And as you progress closer to surgery, the diet may become more restrictive/specific. If your trust your surgeon, trust their process!