Association between the dietary index for gut microbiota and circadian syndrome: a cross-sectional study from NHANES 2007–2018

Circadian Syndrome (CircS) is an epidemiologic construct that combines metabolic abnormalities with features related to sleep and mood and has been associated with adverse health outcomes. The dietary index for gut microbiota (DI-GM) is a dietary proxy index reflecting adherence to dietary patterns potentially related to gut microbial composition, but its relationship with CircS remains unclear. A total of 18,491 adults from NHANES 2007–2018 were analyzed using survey-weighted logistic regression, restricted cubic spline (RCS) modeling, subgroup analysis, and sensitivity analysis. Associations between individual DI-GM components and CircS were further evaluated. Nine machine-learning algorithms were used to assess classification performance and model interpretability based on area under the curve, calibration, decision-curve analysis, and Shapley additive explanations. Mediation analyses were conducted to evaluate whether body mass index (BMI) and systemic immune-inflammation index (SII) may partly account for the observed association. Higher DI-GM scores were inversely associated with CircS. Participants in the highest quartile had lower odds than those in the lowest (OR = 0.693, 95% CI 0.603–0.797; P for trend < 0.001). RCS analysis suggested an overall inverse association, with no strong evidence of nonlinearity (P overall < 0.001; P nonlinearity = 0.130). Subgroup analyses indicated possible variation by poverty-income ratio, ethnicity, and education. Several DI-GM components differed by CircS status. Machine-learning models showed moderate classification performance, and the incremental contribution of DI-GM was limited. Mediation analyses suggested that BMI, and to a lesser extent SII, may partly account for the association between DI-GM and CircS. Among U.S. adults in NHANES 2007–2018, higher DI-GM scores were inversely associated with CircS. Further longitudinal studies are needed to clarify the temporal relationship between dietary patterns represented by DI-GM and CircS.