The Conundrum of XenomiRs and Human Health

MicroRNAs (miRNAs) are small, noncoding RNAs involved in posttranscriptional gene regulation in both animal and plant. miRNAs derived from edible plants, referred to as xenomiRs, are proposed to cross-kingdom barriers and to modulate mammalian gene expression. However, this dietary xenomiR hypothesis remains controversial, given numerous inconsistencies and conflicting evidence regarding stability, bioavailability, and functionality of xenomiRs in mammals. Despite promising findings, including reports of plant-derived miRNAs influencing mammalian gene expression in vitro and in animal models, evidence remains inconclusive in humans. Several independent investigations have reported contradictory findings, emphasizing reproducibility lack in identifying and validating the transfer of xenomiRs from plants to mammals, which has raised concerns about the robustness, reliability, and biological significance of some results. Additionally, no direct molecular evidence currently demonstrates that plant xenomiRs bind to mammalian silencing machinery. Although the concept of plant-derived xenomiRs holds significant potential, future research must address unresolved technical and biological limitations. If validated, this hypothesis may represent a novel avenue for epigenetic modulation through dietary intervention in precision medicine and personalized nutrition. This comprehensive narrative review critically provides an overview of the dietary xenomiR hypothesis, specifically focusing on those derived from edible plants. We summarize the current evidence regarding xenomiR cross-kingdom communication potential, and we discuss technical and biological challenges that impede their validation. We also explore the speculative yet plausible scenario that dietary miRNAs may act locally on the microbiota rather than systemically.