Back in the 1970s when the powdered "instant breakfast" craze was in full swing, a magazine published a recipe for a healthier, less expensive alternative. Basically it consisted of 1/2 cup of milk, 1/2 cup of orange juice, a raw egg, and half a banana, all run through the blender.
I don't know if that constitutes what, today, is called a "smoothie", but owing to the speed with which this could be prepared, this was our regular weekday breakfast for several years.
Of course, this was back when it was still safe to eat raw eggs.