Dietary Fiber Supplementation Reduces Systolic Blood Pressure in High-Risk Patients with Type 2 Diabetes and Hypertension: A Secondary Analysis of a Randomized Trial

Abstract

Background/Objectives: Dietary fiber supplementation has been associated with blood pressure (BP) reduction, but evidence comparing soluble (SDF) and insoluble (IDF) fiber types in high-risk populations is limited. This study aimed to compare the effects of SDF and IDF supplementation on BP and to explore correlations between changes in BP and alterations in gut microbiota composition and serum biomarkers in adults with type 2 diabetes (T2D) and hypertension. Methods: This secondary analysis was based on a 12-week, randomized, double-blind, parallel-group clinical trial. Thirty-five adults with T2D and hypertension were assigned to receive either 5 g/day of oat β-glucan (SDF, n = 19) or microcrystalline cellulose (IDF, n = 16). BP, gut microbiota composition (quantitative polymerase chain reaction; qPCR), and inflammatory biomarkers were assessed at baseline and after the intervention. Results: The mean age of the participants was 50.7 ± 5.7 years, and 77% were female. Both groups exhibited comparable reductions in systolic blood pressure (SBP) (SDF: −11.2 ± 20.9 mmHg; IDF: −11.6 ± 17.0 mmHg; p = 0.965 between groups). In the SDF group, significant positive correlations were observed between increases in Firmicutes abundance and changes in diastolic blood pressure (DBP) (r = 0.90, p < 0.01), as well as between increases in Bifidobacterium spp. abundance and changes in DBP (r = 0.90, p < 0.05). Conclusions: Supplementation with either soluble or IDF was associated with reductions in SBP in this sample of adults with T2D and hypertension. The observed associations between changes in gut microbiota composition and BP should be considered exploratory and interpreted with caution. Placebo-controlled studies are required to confirm these findings and elucidate the underlying biological mechanisms.