The Role of Diet and the Gut Microbiota in the Obesity-Colorectal Cancer Link.

Obesity is positively associated with colorectal cancer (CRC) risk. Diet not only contributes to obesity, but also strongly influences the gut microbiota, a factor that is thought to independently affect CRC. To isolate the role of obesity-associated gut microbiota in CRC and to assess the impact of diet composition on this relationship, we transplanted the gut microbiota from donor mice that developed obesity or remained lean on a high-fat diet (HFD), Western diet (WD), or low-fat diet (LFD) into antibiotic-treated recipient mice that subsequently received azoxymethane to induce CRC. We hypothesized that the obesogenic diets of the donor mice, rather than their obesity status, would be a stronger driver of gut microbiota-mediated CRC development. Interestingly, while evidence supporting our hypothesis was observed, differential effects on CRC outcomes based on the type of obesogenic diets were found, such that HFD-associated gut microbiota promotes tumor incidence whereas WD-associated gut microbiota promotes tumor growth. Significantly enriched bacterial taxa present before tumor induction may be mediating these results through intestinal permeability or inflammation, such as in mice received HFD-associated gut microbiota, and in mice received WD-microbiota. Overall, our results demonstrated that diet drives the gut microbiota-derived impact on CRC development.