Kefir is a fermented dairy product similar to yogurt, but thinner and meant for drinking. Similar to sourdough, kefir is made from a starter. The starter is primarily made of probiotics (called kefir grains), yeast, and milk proteins.
The dairy beverage originated in Eastern Europe and has since been commercialized in other regions of the world, including the U.S., Canada, and Great Britain.
Integrative gastroenterologist Martin Singh, M.D. tells mbg, “just make sure to avoid kefir with added sugar and flavorings.” Instead look for plain, full-fat varieties.
And while not technically kefir, there are aqua kefirs or water-based kefirs, which are a good dairy-free option if you’re extremely sensitive to lactose. You can make your own water kefir at home or purchase the sparkling beverage from brands like GT’s Living Foods.