Bioactive phytochemicals and their potential roles in modulating gut microbiota

Dietary phytochemicals, including polyphenols, sulfur-containing compounds, terpenoids, polysaccharides, saponins, pigments, and phytohaemagglutinins, have antioxidant, anti-inflammatory, antiviral, and cancer-preventive or therapeutic properties. Upon entering the body, these compounds pass through the stomach, liver, small intestine, and colon in that order. Bacteria play an important role in the absorption and processing of dietary phytochemicals in the small intestine and in the large intestine. However, the specific processes by which dietary phytochemicals are absorbed and metabolized in the host colon have not been elucidated. This paper describes the metabolism of phytochemicals (including polyphenols, terpenoids, and plant organosulfides) in the colon and describes the roles played by these dietary phytochemicals in the colon, with emphasis on their effects on the gut microbiota. Upon entry into the host, phytochemicals are absorbed and metabolized mainly in the colon, and the differences in their absorption and metabolism are largely due to differences in the colonic microbiota. Moreover, phytochemicals can be absorbed in the intestine by acting on them through enzymes produced by intestinal cells and stem cells, or by interacting with the intestinal flora, thus ameliorating the associated diseases.