Association Between Plant-Based Diet Quality and Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD) in the Multiethnic Cohort Study

Background: Metabolic dysfunction-associated steatotic liver disease (MASLD), formerly non-alcoholic fatty liver disease (NAFLD), is a growing public health concern with limited effective treatments. Diet quality may influence MASLD risk, yet the role of plant-based diet quality across diverse populations remains unclear. Objective: To evaluate the associations of plant-based dietary patterns with liver fat content or MASLD prevalence in multiethnic older adults. Methods: We analyzed cross-sectional data on 1,598 participants in the Adiposity Phenotype Study (APS), nested within the Multiethnic Cohort Study. Scores for three established plant-based diet indices were computed from food frequency questionnaire responses: overall plant-based diet index (PDI), healthful plant-based diet index (hPDI), and unhealthful plant-based diet index (uPDI). Liver fat was measured using MRI, and MASLD was defined, among participants reporting zero to low alcohol intakes. Multivariable linear models of liver fat and logistic models of MASLD were used to estimate their associations with the plant-based diet indices, adjusting for demographic, lifestyle, and anthropometric covariates. Results: Higher hPDI scores were associated with lower liver fat content (adjusted mean for 4th (5.39) vs. 1st quartile (6.52) and reduced likelihood of MASLD (OR for 4th vs. 1st quartile = 0.58 (95% CI: 0.41-0.81). When stratified across five racial and ethnic groups, stronger inverse associations were observed among Latino and White participants (p-heterogeneity = 0.001) than among African American, Japanese American, or Native Hawaiian participants. No consistent associations were observed for PDI or uPDI. Among hPDI components, higher nut and lower animal fat intakes were associated with lower liver fat and MASLD. Conclusions: Greater adherence to a healthful plant-based diet is associated with lower liver fat and MASLD prevalence, with some racial and ethnic variation. These findings underscore the importance of plant-food quality and may inform dietary strategies for MASLD prevention in heterogeneous populations.