Crenita, because SBD is a diet that focuses on eating less processed food, using a pre-prepared liquid replacement for your snacks isn't something that's necessarily recommended. However, there's no reason why you can't make your own protein smoothies. Lots of us do it!
You just have to be very careful to look at the ingredients on your protein powder to make sure it doesn't have any sugar. I use a whey-based one from Wegman's that is made with Stevia and it works great. I make my smoothies this way:
1 cup or so of frozen fruit (this eliminates the need for ice, which keep it from getting diluted)
1/2 to 1 cup of Plain FF yogurt
FF/Skim milk, as needed
SF syrup (flavor of choice) to taste
Scoop of SF protein powder
1-2 T of Psyllium husk (I find that makes it very filling for me!)
Blend, adding milk, as needed, to ensure the blender can do its job.
JLN, we haven't mentioned protein powder in a while, but there have been some discussions about it in the past. Try searching the forum for more.