Buttermilk

Buttermilk can be substituted for cream in many recipes: a half cup of buttermilk has 1 gram of fat but the same serving of light cream has 31 grams.

Encyclopedia of Foods. A Guide to Healthy Nutrition

Traditionally, buttermilk was the liquid left after churning butter, now it's commonly cultured milk.

Store buttermilk in the refrigerator and use by the expiration date on the container, typically within one to two weeks. Once opened, keep it tightly sealed.