Kefir is a fermented milk drink that is popular in the middle east, parts of the Mediterranean, eastern Europe and Russia. It is prepared by inoculating milk (cow, camel, goat, sheep or even soy milk, almond milk) with kefir grains. Kefir grains consist of a complex living culture of yeasts and bacteria. The organisms have been shown to inhibit both salmonella and E. Coli in the laboratory. Raw milk has traditionally been used to make kefir. Unless otherwise noted, the discussion below refers to kefir and other fermented drinks made from cow's milk.
Fermented milk has been shown in one study to have a protective effect against liver cancer in experimental mice. Similarly, lactobacilli strains common to fermented milk have been shown to possess inhibitory and cytotoxic activity towards human bladder cancer cells. Lactic acid bacteria from fermented milk drink also have been shown to have antiproliferative activity against colon cancer cells. However, one study found that kefir with a 3.5% fat content appeared to stimulate chemically-induced colorectal tumors in experimental rats compared to both 1.1% fat kefir and 1.1% fat sterilized milk.
Breast cancer-related effects of consuming kefir
Kefir has been shown to have antiproliferative activity against hormone receptor positive (ER+/PR+) human breast cancer cells and this anticancer effect was observed at much lower concentrations than similar effects of yogurt. Several studies have demonstrated that milk fermented with L. helveticus decreased the growth rate of mammary tumors in experimental rats and that this involved decreased production of pro-inflammatory cytokines, including IL-6, which is implicated in estrogen synthesis. Kefir is also a good source of conjugated linoleic acid (CLA), which has been shown to inhibit the growth and migration of breast cancer cells.
A Swedish study of the relationship between various fats in the diet and risk of breast cancer for women aged at least 50 found that fat from fermented milk products was negatively associated with breast cancer risk.
Kefir should be avoided during radiation treatment because it has been shown to protect cells against cell death caused by radiation damage, raising the possibility that it will lessen the cytotoxic impact of radiation on breast cancer cells.
Below are links to recent studies concerning this food. For a more complete list of studies, please click on kefir.