Originally, buttermilk was the liquid left after butter had been churned. In modern times, commercial producers add bacteria to milk which gives buttermilk its distinctive thickened texture and tangy taste. Some producers add flecks of butter as well, to give their product an authentic appearance. The U.S. Department of Agriculture lists buttermilk as an acceptable variation in its recommendations for two to three daily servings from the milk, yogurt and cheese food group. Like milk, buttermilk may offer health benefits.

The recommended daily calcium requirement is between 1,000 to 1,200 milligrams per day for most men and women and 1,300 milligrams per day for children 9 to 13, according to the National Institutes of Medicine. One cup of buttermilk provides 284 milligrams of calcium, compared to 299 milligrams of calcium in 1 cup of milk according to the USDA National Nutrient Database.

Although dairy products are not the best source of lean protein recommended by the Dietary Guidelines for Americans, they can provide some of the protein that your body needs for good health. Cup for cup, buttermilk and milk contain about the same amount of protein -- buttermilk contains 8.11 milligrams of protein and milk contains 8.26 milligrams according to the USDA National Nutrient Database.

The USDA National Nutrient Database states that buttermilk contains vitamin A, vitamin C and a number of B vitamins, including thiamine, riboflavin, niacin and pantothenic acid. Buttermilk also contains many essential and trace minerals, including iron, magnesium, phosphorus, potassium and zinc.

Substitute buttermilk whenever milk is called for in recipes, for a slight tangy flavor. Many cooks use it entirely for baked goods such as pancakes, waffles and biscuits. Mark Bittman, author of “How to Cook Everything Vegetarian,” recommends buttermilk in mashed potatoes and in making sauces, dips and salad dressings. He also suggests making fresh cheese with milk, buttermilk and salt.