High-fat diet-mediated dysbiosis promotes intestinal carcinogenesis independent of obesity

Several aspects common to a Western lifestyle, including obesity and decreased physical activity, are known risks for gastrointestinal cancers. There is an increasing amount of evidence suggesting that diet profoundly affects the composition of the intestinal microbiota. Moreover, there is now unequivocal evidence linking a dysbiotic gut to cancer development. Yet, the mechanisms through which high-fat diet (HFD)-mediated changes in the microbial community impact the severity of tumorigenesis in the gut, remain to be determined. Here we demonstrate that HFD promotes tumor progression in the small intestine of genetically susceptible K-rasG12Dint mice independent of obesity. HFD consumption in conjunction with K-Ras mutation mediates a shift in the composition of gut microbiota, which is associated with a decrease in Paneth cell antimicrobial host defense that compromises dendritic cell (DC) recruitment and MHC-II presentation in the gut-associated lymphoid tissues (GALTs). DC recruitment in GALTs can be normalized, and tumor progression attenuated completely, when K-rasG12Dint mice are supplemented with the short-chain fatty acid butyrate, a bacterial fermentation endproduct. Importantly, Myd88-deficiency completely blocks tumor progression in K-rasG12Dint mice. Transfer of fecal samples from diseased donors into healthy adult K-rasG12Dint mice is sufficient to transmit disease in the absence of HFD. Furthermore, treatment with antibiotics completely blocks HFD-induced tumor progression, suggesting a pivotal role for distinct microbial shifts in aggravating disease in the small intestine. Collectively, these data underscore the importance of the reciprocal interaction between host and environmental factors in selecting intestinal microbiota that favor carcinogenesis, and suggest tumorigenesis may be transmissible among genetically predisposed individuals.