Im not sure if we are talking about the same type of smoothie?
Im thinking whole foods normally a mixture of vegetables (leafy greens) and fruits in a blender or something like a nutribullet.
Normally for me its spinach/kale/romaine + one banana+ some other type of fruit like pineapple or mango. Then you can also add flavorless protein powder(or semi skimmed milk/almond milk) and even flaxseeds.
You still get all the nutrients like fiber, but its easier on the gi tract in liquid form.