Kefir is a thick drink made by fermenting milk with kefir grains composed of lactic acid bacteria, yeast and polysaccharides. The grains culture the milk, infusing it with healthy organisms. These types of healthy bacteria or probiotics, are not available in yogurt. They help support the digestive system and prevent the growth of harmful bacteria in the intestines. Vitamins, like vitamin K and B-12, are produced in the gut and the probiotics in kefir facilitate this production.
Furthermore, kefir is more powerful probiotic than yogurt. Kefir in some cases includes up to 3 times more microorganisms than other probiotic drinks. Numbers go even higher with home fermented kefir. Reason lies in process of pasteurization where many good microorganisms are killed in order to preserve the drink and prevent further fermentation, which could cause packaging to explode (some gas is produced in the process).
Kefir also includes some very unique bacteria, which are believed to prevent infections. This includes the probiotic Lactobacillus kefiri, which is unique to kefir. Studies show that this probiotic can inhibit the growth of various harmful bacteria, including Salmonella, Helicobacter Pylori and E. coli (2, 3). Kefiran, a type of carbohydrate present in kefir, also has antibacterial properties (4).
Lastly, some researchers believe that kefir might help prevent cancer. The probiotics in fermented dairy products are believed to inhibit tumor growth by reducing formation of carcinogenic compounds, as well as by stimulating the immune system (5).