Weight loss comes from burning more calories than you consume, which could be calories from any food including sugar. Sugar is a waste of calories because it doesn't contain any nutrients. Reducing sugar can help reduce overall calories because it contains 4 calories per gram. Excessive sugar consumption has been linked to a variety of diseases and health problems. The World Health Organization recommends we get no more than 10% of our daily calories from added
sugars. That would mean the sugar that Slimfast adds is important to count, but it would not include the sugar that naturally occurs in milk.
Slimfast Optima powder mix contains 6 grams of sugar per serving. I guess what really matters here is how many servings you drink. I sometimes drink a glass for breakfast if I'm in a hurry.