Association of dietary index for gut microbiota with metabolic syndrome and its components in US adults: an exploratory cross-sectional mediation analysis using the TyG index

With the rapid development of the global economy, metabolic syndrome (MetS) has become an increasingly prevalent public health concern worldwide. The Dietary Index for Gut Microbiota (DI-GM) is a novel tool designed to evaluate diet quality in relation to gut health. However, the relationship between DI-GM and MetS, as well as its individual components, remains poorly understood. Data were extracted from the National Health and Nutrition Examination Survey (NHANES) spanning 2005 to 2018, focusing on individuals aged 20 years or older. DI-GM scores were calculated based on the average intake from two 24-hour dietary recall interviews. Multivariate weighted logistic regression was used to analyze the association between DI-GM and MetS, including its individual components, while also exploring the potential mediating role of insulin resistance. Secondary analyses included restricted cubic splines (RCS), subgroup analyses, and multiple imputation. After adjusting for confounding factors, higher DI-GM scores were inversely associated with MetS and significantly influenced waist circumference (WC), blood glucose, blood pressure, triglyceride (TG), and high-density lipoprotein cholesterol (HDL-C) levels ( P < 0.05). Scores for favorable gut microbiota were significantly correlated with MetS, WC, HDL-C, and TG ( P < 0.05), while unfavorable gut microbiota scores showed no significant correlation with blood pressure but were significantly associated with MetS and other components ( P < 0.05). After multiple interpolations and subgroup analyses, most of the results were consistent with each other. RCS revealed both linear and nonlinear associations between DI-GM and MetS and its components. Insulin resistance exhibited a significant mediating effect (DI-GM: 45.98%; beneficial gut microbiota: 66.6%; unfavorable gut microbiota: 33.29%). Higher DI-GM was associated with lower odds of prevalent MetS and several MetS components. The TyG index statistically accounted for part of this association, although the cross-sectional design and overlap between TyG and MetS components limit causal and mediation interpretations. These findings suggest that dietary patterns characterized by higher DI-GM scores are associated with more favorable metabolic health.