Consumption of a High‐fiber Diet Improves Systolic Blood Pressure and Vascular Endothelial Function and May Reduce Oxidative Stress in Middle‐aged to Older Adults
Authors: Casso Abigail G. , Burnsed‐Torres Marissa L. , Lubieniecki Kara L. , Rossman Matthew J. , Adam Emily C. , Lally Hannah M. , Chonchol Michel , Davy Kevin P. , Seals Douglas R. , Brunt Vienna E. 
Published: May 2022

Aging is the primary risk factor for the development of cardiovascular diseases (CVD), largely due to increases in systolic blood pressure (SBP) and oxidative stress‐related impairments in vascular endothelial function. Higher intake of dietary fiber is associated with reduced CVD risk. In healthy late middle‐aged to older (MA/O) adults, limited evidence indicates high‐fiber diet interventions improve SBP, but whether a high‐fiber diet improves endothelial function with aging is unknown.PurposeWe tested the hypothesis that a high‐fiber diet would, in addition to reducing SBP, improve endothelial function and reduce oxidative stress in healthy MA/O adults.MethodsWe performed a controlled feeding study in which 14 MA/O adults (8F/6M; age: 69 ± 5 years) consumed an isocaloric high‐fiber diet (30‐35 g/day) for 7 days. Diets also contained 60% total carbohydrates, 15% protein, 25% fat, and 12‐15% sugar. Baseline (pre) measures were performed under habitual diet conditions (26 ± 6 g fiber/day). On days 0 (pre) and 7 (post) of the diet, endothelial cells were collected via venous endovascular biopsy, and endothelial function was assessed by brachial artery flow‐mediated dilation (FMD) following 20 minutes of intravenous infusion of saline (volume control) or the antioxidant ascorbic acid (0.06 g/kg fat‐free mass in 100 mL saline at 5 mL/min; N=12), to determine whether any improvements in endothelial functional following the high‐fiber diet were due to reduced oxidative stress.ResultsConsumption of a high‐fiber diet reduced SBP (pre vs. post: 120 ± 3 vs. 116 ± 3 mmHg, p<0.01) and improved endothelial function by ~30% (pre vs. post: 4.1 ± 0.5 vs. 5.3 ± 0.7 %, p=0.03). Abundance of nitrotyrosine (NT), a marker of oxidative stress, in endothelial cells from a subset of subjects (N=6) was lower after the high‐fiber diet (pre vs. post: 0.43 ± 0.16 vs. 0.29 ± 0.12 A.U., p=0.08). At baseline, infusion of ascorbic acid increased FMD by 2.2 ± 0.7 %Δ units (p=0.01 vs. saline), indicating tonic suppression of endothelial function by oxidative stress under habitual diet conditions. Ascorbic acid still increased FMD post‐high‐fiber diet but to a lesser extent (+1.2 ± 0.6 %Δ units, p=0.06 vs. saline), and differences in FMD pre vs. post high‐fiber diet were abolished by ascorbic acid (6.3 ± 0.9 vs. 6.6 ± 0.9 %, p=0.68). These data suggest that the high‐fiber diet improved FMD in part by reducing oxidative stress.ConclusionsHigh‐fiber diet consumption improves SBP in healthy MA/O adults with normal baseline levels and induces clinically significant improvements in FMD possibly via reductions in vascular oxidative stress and tonic oxidative stress‐related suppression of endothelial function. These results suggest that a high‐fiber diet may reduce CVD risk, at least in part, by mitigating increases in SBP and oxidative stress‐related impairments in endothelial function with aging.