Dietary Intake of Micro- and Nanoplastics: Potential Adverse GI Effects on Microbiome, Inflammation, and Neoplasia.

Micro- and nanoplastics (MNPs) are pervasive in food-contact environments and the human diet, positioning the gastrointestinal (GI) tract as the primary portal of entry and a plausible site of early biological effects. Human exposure is supported by detection of microplastics in stool and colon tissue, and emerging clinical studies report associations between fecal microplastic burden and GI disease states, including inflammatory bowel disease (IBD) and colorectal cancer (CRC). Preclinical studies provide mechanistic plausibility, reporting that ingested MNPs can modulate microbial ecology, alter mucus membrane integrity, increase intestinal permeability through changes in cellular tight junction biology, and induce inflammatory gene expression. These effects can vary by MNP polymer type, particle size/shape, aging state, and exposure dose. Human-relevant experimental platforms increasingly demonstrate size- and concentration-dependent uptake and host responses while revealing substantial inter-individual variability. We synthesize current evidence on dietary sources and key physiochemical properties as they relate to mechanistic pathways connecting MNP exposure to dysbiosis-immune activation-neoplasia axes, in addition to methodological limitations that constrain current clinical utility. Further research including standardized biomonitoring and exposure protocols, environmentally realistic chronic low-dose mixtures, longitudinal human cohorts, and interventional designs that test whether exposure reduction modifies GI inflammation biomarkers and cancer-relevant pathways are critical to clarifying causality.