As these shakes are Meal Replacements they need by law to contain a certain amount of energy (number of Calories) so as to provide the body with sustenance. Some of this energy/Calories is provided by sugars. The majority of sugars in the FAST Shakes is naturally occurring lactose (milk sugar) which is coming from the milk ingredients used in these shakes rather than added sugars.
Not all protein shakes are suitable as meal replacement shakes. Some high protein, low carbohydrate and low calorie protein shakes may not be designed to be used in place of meals and may not meet the requirements to be meal replacements.
I hope this helps clarify.
BT Nutritionist 🙂