Hi, i am not a doctor , I don't know what is in slim fast or what weight watchers advise re what to eat and can only tell you of my own personal experience…but I have been trying low carb high fat diet ( and also metformin and Victoza) and my sugars are amazing, for me at least it truly is about the amount of carbs I eat and by making some adjustments I have brought sugars down and can eat a varied diet, I know I'm on meds and I know this also helps me to control sugars but I honestly think the reduction from my first week of testing which started at 21 after at least 8 hours fasting to an average of 4.5 3 months later is not meds alone, there is a lchf forum, really useful, maybe this can help you to bring those levels into safer levels? Good luck