Lactic acid bacteria and cancer: mechanistic perspective

Colorectal cancer is one of the most important causes of cancer morbidity and mortality in Western countries. While a myriad of healthful effects have been attributed to the probiotic lactic acid bacteria (LAB), perhaps the most controversial remains that of anticancer activity. It should be pointed out that there is no direct experimental evidence for cancer suppression in man as a result of consumption of lactic cultures in fermented or unfermented dairy products. However, there is a wealth of indirect evidence, based largely on laboratory studies, in the literature. The precise mechanisms by which LAB may inhibit colon cancer are presently unknown. However, such mechanisms might include: alteration of the metabolic activities of intestinal microflora; alteration of physico-chemical conditions in the colon; binding and degrading potential carcinogens; quantitative and/or qualitative alterations in the intestinal microflora incriminated in producing putative carcinogen(s) and promoters (e.g. bile acid-metabolising bacteria); production of antitumourigenic or antimutagenic compounds; enhancing the host's immune response; and effects on physiology of the host. These potential mechanisms are addressed in the present paper.