This study was aimed to review recent reports on antitumor activity of lactic acid bacteria
including the relationship among the gut microflora, nutritional factors and carcinogenesis
in human and animals. The fecal bacterial enzymes, β-glucuronidase,
nitroreductase, and azoreductase were shown to play an important role in the incidence
of colon cancer. These enzyme activities in feces were increased on a Western (high
fat and animal protein) diet, but reduced by consuming of 1～3×1010 Lactobacilli per
day. High consuming (≥225 g/day) of fermented milk products, even the people on
a Western diet were epidemiologically revealed to be at low risk for colon and breats
cancer. This antitumor effect is attributed to reducing the production of harmful bacterial
enzymes such as β-glucuronidase, nitroreductase, and azoreductase due to decreasing
of putrefactive bacteria in colon. In animal models having tumors, Lactobacilli cultures
also significantly suppressed the growth of sarcoma, leukemia and carcinoma. The
antitumor effects of lactic acid bacteria are supposed to be host-mediated and
dependent on the activation of non-specific effector cells such as macrophages or
natural killer cells.

Keywords: Lactic acid bacteria, Cancer, Antitumor, Fermented milk