Smoothies don’t necessarily have to contain milk, or any dairy-based ingredient for that matter. The liquid base of a smoothie can instead be made from juices or purees consisting of fruits, vegetables, legumes, leaves, and more.  Dairy substitutes are popular for vegetarian and vegan smoothies. These can include nut milks or other plant-based liquids. The mixture can be thinned and cooled by introducing crushed ice as well.