Milk, yoghurt, and cottage cheese are common smoothie ingredients, but they don't work well for everyone. Approximately 65 percent of the world population has a decreased tolerance to lactose (the sugar found in milk products). Visser notes that, "Conventional dairy can be very inflammatory from the denatured proteins that our bodies often mark as allergenic, to the poor food, hormones, and antibiotics fed to the cows. This can cause a cascade of inflammation and possible gut-related issues."
The good news is that there are loads of alternatives, and many of them are available at major grocery stores. If you are simply looking for a high-quality, organic dairy milk, Organic Valley is a good option. You could also swap out dairy milk for almond, cashew, or coconut milk, and yoghurt for a nondairy variety.
Psst . . . you should try out a few of these dairy-free smoothie recipes while you are at it.