Functional Foods and Micro- and Nanoplastics: Advances in Precision Nutritional Medicine for Oral–Gut–Brain Axis Health

Microplastics and nanoplastics (MNPs) are emerging environmental pollutants due to their persistence and bodily accumulation. Recently, functional foods have received much attention for their ability to reverse or block MNP damage for therapeutic purposes and the potential risk of developing oral–gut–brain axis disorders. Among these, artichoke, spirulina algae, Opuntia ficus-indica, pterostilbene, hydroxycinnamic acids, and quinic acid are rich sources of polyphenols. These bioactive ingredients, especially when combined with probiotics and prebiotics, exhibit significant antioxidant and anti-inflammatory potential by activating nuclear factor erythroid 2-related factor 2 (Nrf2) signaling and cellular resilience enzymes. Nrf2 activation enhances cellular resilience response, and it may preserve oral epithelial barrier (OEB), intestinal epithelial barrier (IEB), and blood–brain barrier (BBB) integrity, while modulating oral pathogens, gut microbial dysbiosis, and neuroinflammatory processes. However, most of the available evidence supporting these mechanisms derives from in vitro and animal studies, whereas clinical evidence in humans remains limited. Perturbations of Nrf2 due to circulating MNPs may exacerbate selective susceptibility to oral, gut, and nervous system disorders, including Alzheimer’s disease (AD). Although these findings are biologically plausible, the causal relationships and their clinical relevance have not yet been fully established. This review discusses the role of functional foods in maintaining oral–gut–brain health through Nrf2-mediated mechanisms that may mitigate MNP-induced inflammation and reactive oxygen species (ROS). The review also examines emerging concepts in precision nutritional medicine, including individual variability in dietary responses, microbiome-related factors, and future personalized strategies for populations exposed to MNPs. Finally, current knowledge gaps, the scarcity of human studies, and the challenges in translating preclinical findings into clinical practice are highlighted, emphasizing the need for further translational and clinical research.