Analysis of 9,616 middle-aged adults revealed five specific gut bacteria species that appear to mediate the protective effects of healthy diets against metabolic dysfunction-associated steatotic liver disease (MASLD). Participants following Mediterranean, plant-based, anti-inflammatory, and other quality dietary patterns showed lower prevalence of fatty liver disease and reduced levels of Flavonifractor plautii, Dysosmobacter welbionis, Ruthenibacterium lactatiformans, Bilophila wadsworthia, and Phocea massiliensis. These findings illuminate a critical mechanistic pathway in liver health that has broad implications for preventing what's becoming the world's leading cause of chronic liver disease. The gut-liver axis represents a promising therapeutic target, suggesting that dietary interventions might work partly by reshaping harmful bacterial populations. However, this cross-sectional study cannot establish causation—whether diet changes gut bacteria which then affects liver health, or whether other factors drive all three variables simultaneously. The 138 total bacterial species identified provide a rich foundation for designing targeted probiotic or prebiotic interventions. As this work awaits peer review, the specific bacterial targets and mediation pathways require validation through longitudinal studies and clinical trials to confirm their therapeutic potential.