I did low carb liquids- mostly protein shakes, Greek yogurt and fruit & veggie smoothies, and a lean & green dinner each night. Kept around 1,000 calories and lost 20+ pounds. I think it was around 4 weeks?
Btw, you're gonna have to learn that surgeons DO NOT always know best when it comes to diet advice. I used to have that same perception of "well, he's the doctor, he knows best" but that's not necessarily true. They may know best about slicing and dicing our insides, but usually not about diet and nutrition.