Kefir is a fermented milk drink that is similar to yogurt. Like yogurt, it is made by using bacteria to ferment milk, which gives it a tangy flavor. Unlike yogurt, kefir is also made with yeast, which turns lactose into carbon dioxide, producing bubbles.
Kefir contains three times the amount of probiotics present in yogurt, providing even greater numbers of the good bacteria that stop harmful bacteria from living in the gut. Kefir is also valued for its calcium, B vitamins and phosphorous content, as well as for being a low-fat source of protein. A small number of studies have shown that kefir assists in the digestion of lactose, but further research in this area is required.