Association between dietary fiber intake and mortality in populations with accelerated biological aging: a study based on NHANES 1999-2018 data

To investigate associations of total dietary fiber intake (DFI) and fiber sources with all-cause and cardiovascular mortality in individuals with accelerated biological aging, and to assess inflammation's mediating role. This study included 9,322 adults with accelerated aging from National Health and Nutrition Examination Survey (NHANES) 1999-2018. Weighted Cox models examined associations between DFI and mortality. Restricted cubic spline, subgroup, and mediation analyses were applied. Compared to the lowest quartile, the highest DFI quartile had 35% lower all-cause mortality risk [hazard ratio (HR) = 0.65, 95% confidence interval (CI): 0.45-0.92] and 49% lower cardiovascular mortality risk (HR = 0.51, 95% CI: 0.30-0.87). Each 9.74 ‍g/day increase in DFI was associated with an 18% (HR = 0.82, 95% CI: 0.71-0.94) and 24% (HR = 0.76, 95% CI: 0.63-0.93) reduction in all-cause and cardiovascular mortality risk, respectively. Only grain-based fiber showed a significant inverse association with both outcomes. Mediation analysis indicated inflammation partially mediated the association, with the monocyte-to-lymphocyte ratio having the strongest effect. In adults with accelerated aging, higher DFI, particularly from grains, is inversely associated with all-cause and cardiovascular mortality, partly by attenuating systemic inflammation, suggesting a potential nutritional intervention to improve prognosis.