The association of diet, gut microbiota and colorectal cancer: what we eat may imply what we get

Abstract

Despite the success of colonoscopy screening and recent advances in cancer treatment, colorectal cancer (CRC) still remains one of the most commonly diagnosed and deadly cancers, with a significantly increased incidence in developing countries where people are adapting to Western lifestyle. Diet has an important impact on risk of CRC. Multiple epidemiological studies have suggested that excessive animal protein and fat intake, especially red meat and processed meat, could increase the risk of developing CRC while fiber could protect against colorectal tumorigenesis. Mechanisms have been investigated by animal studies. Diet could re-shape the community structure of gut microbiota and influence its function by modulating the production of metabolites. Butyrate, one of the short-chain fatty acids (SCFAs), which act as a favorable source for colonocytes, could protect colonic epithelial cells from tumorigenesis via anti-inflammatory and antineoplastic properties through cell metabolism, microbiota homeostasis, antiproliferative, immunomodulatory and genetic/epigenetic regulation ways. In contrast, protein fermentation and bile acid deconjugation, which cause damage to colonic cells through proinflammatory and proneoplastic ways, lead to increased risk of developing CRC. In conclusion, a balanced diet with an increased abundance of fiber should be adopted to reduce the risk and prevent CRC.

Keywords: colorectal cancer; fat; fiber; gut microbiota; metabolites; protein.

Figure 1

The association of diet, gut microbiota and CRC

Figure 2

Diets influence CRC risk via gut microbiota and associated metabolites. This figure shows the effect of two different types of dietary patterns on gut microbiota and associated metabolites. Gut bacteria can promote CRC by metabolizing oncogenic dietary/digestive components such as protein and bile acids into metabolites such as secondary bile acids and hydrogen sulfide. In contrast, gut microbiota can protect against CRC by metabolizing beneficial dietary/digestive components such as plant-based polyphenols and fiber into metabolites such as butyrate. Bacteria and their metabolites can have direct effects on colonocytes via barrier dysfunction, epithelial proliferation, inflammatory, DNA damage, genotoxic ways, etc