Association of dietary fiber with all-cause mortality in U.S. adults with diabetes: Mediating role of the systemic immune-inflammation index

Abstract

Dietary fiber is recommended in diabetes management for its potential anti-inflammatory effects, but currently, the association between fiber intake, systemic inflammation, and long-term survival in adults with diabetes remains uncertain. This cohort study analyzed data from 3894 U.S. adults with diabetes across 10 National Health and Nutrition Examination Survey cycles (1999–2020). Fiber intake levels (grams of fiber per kilogram of body weight, g/kg) was assessed via dietary interviews, and mortality outcomes were linked to National Death Index records through 2019. The systemic immune-inflammation index (SII) was calculated using platelet, neutrophil, and lymphocyte counts. Cox proportional hazards models evaluated associations between fiber intake and all-cause mortality, adjusted for demographics, lifestyle factors, and comorbidities. Mediation analysis quantified SII’s role in mortality risk reduction. Higher fiber intake levels demonstrated a dose-dependent inverse relationship with all-cause mortality (P < .001). In fully adjusted models, the 3rd quartile (Q3) of fiber intake levels showed the lowest mortality risk (hazard ratio = 0.47, 95% confidence interval = 0.37–0.68). The association attenuated slightly in Q4, possibly indicating a threshold effect. Mediation analysis revealed that 13.07% (95% confidence interval = 6.85%–18%) of the mortality reduction was attributable to SII downregulation. Increased dietary fiber intake levels are associated with reduced all-cause mortality in diabetic populations, with a possible mediating factor being the reduction in systemic inflammation levels among U.S. adults with diabetes. These findings support integrating fiber-rich diets into diabetes management protocols.