Association of the dietary index for gut microbiota and dietary inflammation index with metabolic dysfunction-associated steatotic liver disease and metabolic alcohol-associated liver disease

Metabolic dysfunction-associated steatotic liver disease (MASLD) and alcohol-associated metabolic dysfunction-associated liver disease (MetALD) are significant public health concerns, with diet playing a pivotal role in their pathogenesis. Aims: Using data from the National Health and Nutrition Examination Survey (NHANES) 2007-2018. This study investigates the associations of the dietary index for gut microbiota (DI-GM), dietary inflammatory index (DII), and their combined effects with MASLD/MetALD, while exploring the mediating roles of inflammation and metabolic dysfunction. Data from the 2007 to 2018 NHANES included 9,529 participants. DI-GM and DII were calculated using 24-hour dietary recalls. Inflammatory and metabolic biomarkers-including triglyceride-glucose (TyG) index, metabolic score (MS), C-reactive protein (CRP), systemic immune inflammation index (SII), and systemic inflammatory response index (SIRI)-were analyzed. Multivariable logistic and linear regression, subgroup analyses, and restricted cubic spline (RCS) models assessed associations and dose-response relationships. Mediation analysis evaluated the roles of inflammatory and metabolic markers. Higher DI-GM scores were significantly associated with reduced MASLD (OR = 0.59, 95% CI: 0.46-0.75) and MetALD (OR = 0.57, 95% CI: 0.46-0.70). Conversely, higher DII scores were positively associated with MASLD (OR = 1.57, 95% CI: 1.23-2.01) and MetALD (OR = 1.40, 95% CI: 1.13-1.75). DI-GM was inversely associated with inflammation and metabolic markers (TyG: β= -0.05, MS: β= -0.11, CRP: β= -0.12, SII: β= -0.08, SIRI: β= -0.09), while DII exacerbated these markers (TyG: β= 0.06, MS: β= 0.18, CRP: β=0.14, SII: β= 0.11, SIRI: β= 0.10). The combined effects of DI-GM and DII further demonstrated that a gut microbiota-healthy and anti-inflammatory diet synergistically reduced MASLD (OR = 0.59, 95% CI: 0.43-0.81) and MetALD risks (OR = 0.58, 95% CI: 0.44-0.76). Mediation analysis confirmed that inflammation and metabolism significantly mediated the diet-disease associations (p < 0.05). Higher DI-GM and lower DII are associated with reduced MASLD/MetALD risks, partially mediated by alleviating systemic inflammation and metabolic dysfunction. These findings highlight dietary interventions targeting gut microbiota and inflammation as strategies for early prevention of MASLD and MetALD.