For the longest time, I have used peanut paste in my smoothies to add protein, rich taste, and texture.
It's one of my all-time favorites. 
 
Peanut paste is made by adding peanuts to a food processor and running it at low speed until smooth.  You may pause to scare down the sides every half a minute or so.  It will blend after a while and create a creamy paste. 
 
This pasete sold here is 100% natural.