Risk of colon cancer is known to be increased by Western diets that are high in animal fat and low in fibre. A team of researchers has now shown that a short-term diet swap (in terms of fat and fibre content) in individuals from populations at high risk (African American) or low risk (rural South African) of colon cancer is associated with reciprocal changes in indices of cancer risk, such as levels of mucosal biomarkers and microbiota-derived metabolites. Specifically, African American individuals fed a low-fat, high-fibre diet exhibited increased rates of saccharolytic fermentation and butyrogenesis (producing anti-neoplastic metabolites), and reduced synthesis of secondary bile acids (pro-neoplastic metabolites). The findings support increasing fibre consumption and decreasing fat intake as a possible way to reduce the high incidence of colon cancer in African American individuals and other Western populations.