Inadequate Dietary Fibre Intake in Cardiovascular Disease Populations and Its Adverse Impact on Metabolic Health and Longevity: A National Retrospective Cohort Study

Despite the established benefits of dietary fibre for cardiovascular health, it remains unclear whether and how dietary fibre intake, particularly from specific food sources, influences all-cause and cause-specific mortality in populations with established cardiovascular disease (CVD). This cohort study utilised data from the National Health and Nutrition Examination Survey 2003-2018. First, we compared dietary fibre intake between 3952 CVD individuals and 3952 age- and gender-matched non-CVD controls, generated by propensity score matching. Second, Cox proportional hazards regression models were employed to assess the associations of dietary fibre intake and source with all-cause, cardiovascular and cancer mortality in CVD populations. Third, to explore potential underlying mechanisms, we examined the associations of dietary fibre intake with validated biomarkers of metabolic health (triglyceride-glucose index, cardiometabolic index) and systemic inflammation (systemic inflammatory response index, systemic immune-inflammation index) in CVD populations. Adjustments were made for sociodemographic, dietary and health-related covariates. Compared to non-CVD individuals, CVD individuals had significantly lower average dietary fibre intake (15.7 g/day vs. 14.1 g/day, p < 0.001). Individuals with multiple coexisting CVDs exhibited the lowest dietary fibre intake (13.1 g/day). Only 9.3% of males and 11.7% of females met the recommended Adequate Intake standards (30 g/day for males, 21 g/day for females) in the CVD group. Over a median follow-up of 6.3 years, dietary fibre intake was inversely associated with all-cause, cardiovascular and cancer mortality in CVD populations. Compared to the first quartile, the all-cause mortality risk was reduced by 42% (hazard ratio [HR] 0.58, 95% confidence interval [CI] 0.45-0.75), cardiovascular mortality by 52% (HR 0.48, 95% CI 0.29-0.78) and cancer mortality by 50% (HR 0.50, 95% CI 0.24-1.02) in the fourth quartile of dietary fibre intake. In terms of dietary fibre sources, grain and legume/nut fibre had a stronger association with survival benefits than fruit and vegetable fibre. Mechanistic exploration analysis suggests that dietary fibre intake was associated with a decrease in triglyceride-glucose index and cardiometabolic index, but not with the systemic inflammation response index and systemic immune-inflammation index. Both CVD and non-CVD populations exhibited inadequate dietary fibre intake, with the deficiency being more pronounced in the CVD group. Among CVD populations, those with higher dietary fibre consumption had a lower risk of all-cause, cardiovascular and cancer mortality. Our findings highlight a significant and remediable nutritional gap in this high-risk population and underscore the importance of improving dietary fibre intake as a potential supplementary strategy to improve survival in adults with CVDs.