Association of the dietary index for gut microbiota with all-cause and cardiovascular mortality in cardiovascular–kidney–metabolic syndrome: an NHANES-based study

Previous studies link the Dietary Index for Gut Microbiota (DI-GM) to mortality in CKM syndrome, but its robustness and added prognostic value remain unclear. We included 13,286 adults (≥ 20 years) with CKM syndrome from NHANES 2007–2018. Kaplan–Meier curves, weighted Cox regression, restricted cubic splines, subgroup analyses, and sensitivity analyses evaluated associations of DI-GM with all-cause and cardiovascular mortality. Weighted machine-learning analyses further compared DI-GM with the Healthy Eating Index-2015 (HEI-2015), Dietary Approaches to Stop Hypertension (DASH), and Dietary Inflammatory Index (DII), and assessed the relative prognostic contributions of its 14 components. During a median follow-up of 80 months, 1,207 all-cause deaths occurred, including 368 cardiovascular deaths. Each 1-SD increase in DI-GM was associated with 11% and 17% lower risks of all-cause and cardiovascular mortality, respectively (HR = 0.89, 95% CI 0.83–0.95, P < 0.001; HR = 0.83, 95% CI 0.74–0.94, P = 0.003). RCS analyses showed linear inverse associations; significant interactions by age and CKM stage were observed for cardiovascular mortality; and sensitivity analyses supported robustness. DI-GM demonstrated prognostic discrimination comparable to established dietary indices. Component-level analyses revealed the contributions of specific dietary components. DI-GM offers a complementary gut microbiota-based perspective for prognosis and dietary management in CKM syndrome.