Buttermilk actually has no butter in it...

In spite of what the name "buttermilk" might imply, it is not a buttery, high-fat milk. Buttermilk has less fat than ordinary milk even if it doesn't contain any butter. The word "butter" in buttermilk relates to the process of churning butter, which is where this multipurpose fermented beverage got its start. Buttermilk fuels the leavening in baked goods and imparts a tangy flavor and creamy richness to savory and sweet foods.