I used the shakes sold at my doctor's office for my pre-op and post-op. Recently it's been difficult to prep with four children but my nutritionist has recommended a pre-made shake called Premier Protein. It has 30 grams of protein, 1 gram of sugar and only 160 calories and they come in 11-ounce Tetra Pak and they're very filling. The brand that I use for my doctor is called Thorne research Medi Pro Meal Essentials. 30 grams of protein, 7 grams of fiber, and 210 calories. they're great . They're lactose-free gluten-free wheat-free sucralose &Aspartame free and they're very filling and very delicious they even had a chai tea flavor. I buy the premier protein shakes at BJ'S but they only carry chocolate, which is delicious...but I'm already limited with food options so I want variety. You can get all 3 flavors at Sam's or Costco. They're great. Sometimes I have a problem with deciding what to eat what or what I'm in the mood for and with my job and 12 hour shifts sometimes I don't have time to sit down and eat let alone chew slowly so I sip on a a shake as a meal.