Relationship between gut microbiota and colorectal cancer: Probiotics as a potential strategy for prevention

Gut microbiota comprise microorganisms residing in the gastrointestinal tract. Some of these microbiota are implicated in the progression of colorectal cancer (CRC). Here, we highlight studies on the effects of meat intake and fermented foods on characteristics of gut microbiota that can influence colitis-associated factors underlying CRC. Gut microbiota can influence the development and progression of CRC, through influencing factors such as secretion of toxins; enzymes for activating carcinogenesis (including 13-glucuronidase, 13-glucosidase, azoreductase, nitroreductase, and alcohol dehydrogenase); hydrogen sulfide generation; generation of reactive oxygen species and inflammation; secondary bile salt transformation; and products of protein fermentation. Additionally, some studies that the composition of gut microbiota (probiotics) or prebiotics plays an important role in the production of short chain fatty acids, inactivation enzymes for carcinogenesis, antioxidant activities, and inhibition of pathogen colonization. In this review, we discuss various explanatory mechanisms of the relationship between the multifactorial role of the gut microbiota and the development of CRC. Moreover, this review provides fundamental information on dietary fermented food and the gut microbiota, which is helpful for healthy people and those with CRC alike.