From what I understand, the pre-op diet is determined by the surgeon's preference, the patient's BMI and bloodwork. My surgeon did not do a 2-week liquid diet. Instead it was a 2-week diet consisting of:
Morning: New Directions Protein Shake (or Ensure max Protein)
Morning Snack: 2 cup raw non-starchy veggies
Lunch: New Directions Protein Shake (or Ensure max Protein)
Afternoon Snack: New Direction Protein Bar
Dinner: 1/2 cup cooked veggies, 1 serving of fat, 3-4oz lean protein, one serving of carb (max 15g)
Snacks x2 a day: 2 Tbsp of fat free cool whip
On the last day it was only protein shake.
My surgeon said my surgery went amazingly and that I was a model patient to work on. So don't be scared if your surgeon doesn't use the most common pre-op diet. It doesn't make then a bad surgeon and it doesn't mean you will fail.