The Plastic Within: Micro- and Nanoplastics in Human Tissues and the Nutritional Context for Exposure Mitigation.

Background: Microplastics (MPs) and nanoplastics (NPs) are increasingly detected in human tissues, prompting concern about potential biological effects. Yet, for most outcomes, the literature remains dominated by detection studies and preclinical toxicology, with limited human dose-response data. Methods: We conducted a narrative review of peer-reviewed literature (2000-2025), prioritizing human biomonitoring and tissue-detection studies, observational health-outcome studies, and mechanistic evidence that plausibly links exposure to cardiometabolic, reproductive, and neuroinflammatory pathways. Certainty of evidence was appraised using GRADE principles where applicable and explicitly separated from mechanistic plausibility. Results: MPs/NPs have been reported in blood, lung, placenta, atherosclerotic plaques, brain, liver, and testicular tissue. The most clinically salient human outcome signal to date is an association between plaque microplastics and subsequent major adverse cardiovascular events in an observational cohort (hazard ratio 4.53, 95% CI 2.00-10.27). However, polymer quantification approaches vary (particle counts vs polymer mass), contamination control is method-dependent, and inter-study comparability remains limited. Conclusion: The current evidence base supports aggressive exposure reduction as the most defensible "first-line" strategy. Nutritional approaches (dietary fiber, gut-barrier support, and microbiome modulation) are best framed as adjunctive, mechanistically plausible risk-mitigation strategies rather than proven methods to remove plastics from the body. Well-designed human trials and standardized analytical protocols are needed before clinical "detoxification" claims can be justified.