I've used Slim Fast (and Carnation Instant Breakfast) for 30 years, so I can advise you about that (although not about the gall bladder problem.) I use the Slim Fast Chocolate Royale powder mixed with 2% milk, rather than the cans. While I was trying to lose weight, I cut the carbs down by using 1 Tablespoon of the powder (rather than a whole scoop, which equals 3 Tbs.) and 1 teaspoon of Hershey's cocoa. You don't need to add additional sweetener for the cocoa because the 1 Tbs. of the mix has more than enough sugar to sweeten the 1 tsp. of cocoa. I also heat the milk up before I put in the powder and cocoa -- it mixes better and it tastes like hot chocolate.