Gut Check: <i>Lactobacillus johnsonii</i> Harnesses Bile Acids and Reactive Oxygen Species to Suppress High-Fat Diet–Induced Colorectal Cancer

Colorectal cancer is among the most prevalent and deadly malignancies worldwide, with its incidence being closely associated with lifestyle factors, including high-fat diets (HFD). Epidemiologic studies correlate HFD with increased colorectal cancer risk, yet individual susceptibility varies widely, and the underlying drivers remain poorly understood. Recent advances have shifted the paradigm from solely focusing on dietary composition to considering the contribution of host-microbe interactions and microbial metabolite profiles to interindividual differences in the risk of HFD-driven colorectal cancer. In this issue of Cancer Research, Liu and colleagues investigated Lactobacillus johnsonii as a protective bacterium that suppresses HFD-driven tumorigenesis. By promoting the conversion of conjugated bile acids to chenodeoxycholic acid, L. johnsonii triggers mitochondrial dysfunction, thus promoting the production of reactive oxygen species and inducing apoptosis to suppress colorectal cancer development. These preclinical findings provide mechanistic insight into the intersection of bile acid metabolism, gut microbiota, and carcinogenesis, and they lay the groundwork for future translational studies exploring probiotic-based cancer prevention approaches. See related article by Liu et al., p. 4600.