Dietary exposures, microbial ecology and carcinogenesis: An integrated review

The gut microbiome can influence cancer susceptibility, progression, and treatment response. Microbes shape carcinogenesis through direct genotoxicity, epithelial barrier disruption, sustained inflammation, immune modulation, and the biotransformation of diet-derived substrates into bioactive metabolites. Diet is an important modifiable determinant of microbial community composition and function: Western dietary patterns may favour pro-carcinogenic microbial activities, whereas plant-rich, fibre-dense diets can support saccharolytic fermentation and commensal functions. These effects depend on substrate availability, microbial strain and host context. This review centres on colorectal and gastric cancers, with selected evidence from hepatocellular, pancreatic, breast and head-and-neck malignancies. Establishing causality remains central: most human evidence is associative, and mechanistic or interventional evidence is required for therapeutic or preventive translation. This review summarises the mechanistic roles of specific bacterial pathobionts, commensals and fungi across these cancer types, distinguishes observational, experimental and clinical interventional evidence for diet-microbiome interactions, and identifies translational priorities.