They should have given you a pre-op diet according to your BMI. I guess a week or two you should start. I am no expert and my surgery is November 2. My BMI is 38 and 36 on good days. So 3 days before surgery I start a diet of no sugar, no or low carbs, one protein drink in the morning and one in the afternoon. They higher the protein the longer you will stay full. Then for dinner lean chicken, tuna, or turkey only. I can have all the sugar free jello or clear broth that I want. I think it helps the surgery go better for you. May be less gas or something. If your BMI is higher than mine you probably should do a week or 2 before. Your doctor should be able to tell you. From my dieting experience I found that the good oils (olive, avocado is the best) will help you stay full. I need to ask if we can have oils. But always ask your doctor. I am just another patient that has questions too.