Fermented dairy products are those in which microorganisms, most commonly lactic acid bacteria, convert lactose to lactic acid.1 Examples of fermented dairy products include more well-known foods such as yogurt, cottage cheese, sour cream, and cheeses, as well as some items that are less common, including kefir and fermented milk.
There are diverse microorganisms that can be used for this process and they can have different properties and requirements. Products produced during the fermentation process, such as bioactive peptides and compounds, which are reported to have healthful properties and may provide antihypertensive, antimicrobial, and immune-modulatory benefits. In addition, fermentation can enrich the dairy product for vitamins such as B12, folic acid, biotin, and folate, as well as unsaturated fatty acids.
Fermented dairy intake has been evaluated as a potential preventive for cancer. Multiple in vitro and animal studies suggest that fermented dairy may have anticancer properties. Several epidemiologic studies have investigated the association between fermented dairy intake and cancer, although results have been mixed. Some in-human studies have also been conducted to determine if kefir can improve or prevent chemotherapy-induced toxicities or discomfort.
In Vitro and Animal Studies
Many in vitro and animal studies have evaluated the potential anticancer properties of kefir. Kefir is an acidic, effervescent fermented milk that is produced using grains consisting of symbionic lactic acid bacteria and yeast that is a source of vitamins A, K, B1, B2, B5, B12, and C; folic acid; and carotene; as well as several amino acids and multiple minerals.2
A systematic review of 11 studies, including 7 in vitro and 4 animal studies, evaluated the potential chemopreventive effects of kefir.3 In the review, all of the studies demonstrated some anticancer property, primarily antiproliferative or decreased proliferative effects on cancer cells and tumor growth inhibition in animal studies. Other studies have similarly shown that kefir induces apoptosis of acute erythroleukemia, myelogenous leukemia, colon cancer, and breast cancer cell lines.2,4-6 One study demonstrated that kefir decreased proliferation of colon cancer cells by arresting the cell cycle at the G1 phase, and, along with other studies, showed that kefir induces apoptosis through a caspase-dependent pathway.2,7