Is it normal to not lose weight on a pre-op liquid diet?

Hello,
Thank you for your question and congratulations on your upcoming surgery. It is not uncommon for patients to have a difficult time losing weight in the preoperative period. Oftentimes the metabolism can slow as it adjusts to fewer calories. It is also important to ensure you do not have liquid calories sneaking such as sweetened coffees or sodas. This is also an important consideration after surgery.
Best wishes,
Dr. Moein

Check the protein shakes you are using, some are very high in carbs, which stores as fat, so you want to avoid those, also avoid artificial sweeteners!
Find a shake that are clean without stimulants, artificial sweeteners, or sugar.   It makes a huge difference.  Toxins are stored in fat, so you need a protein shake that doesn't add to that toxic load, and helps nourish your body and helps you keep your lean muscle mass.

Hello, 
There are several reasons to have lack in the process. First try to get supervised in your process by a nutritionist and/or bariatric team. Remember that your food intake is small and your body thinks that you are sick and could possibly try to reduce the speed of your metabolism, the stall after the gastric sleeve is normal, this is your body adjusting to the new portions and quality of foods.
Don't get discourage and keep up the good work,