Effects Of Glycemic Index And Dietary Fiber On Postprandial Endothelial Function

Abstract

Endothelial dysfunction is an independent predictor of cardiovascular morbidity and mortality. The postprandial period may be critical in the development of atherosclerosis. Both glycemic index (GI) and dietary fiber have been reported to affect metabolic responses during the postprandial period. PURPOSE: We examined the effects of GI and dietary (predominantly cereal) fiber on postprandial endothelial function in healthy adults. METHODS: Ten adults [5 men; 5 women; mean (SD) age = 40.4 (15.6) yr; weight = 69.9 (11.1) kg; height = 174.2 (9.0) cm] were studied on 4 randomized days at the General Clinical Research Center (GCRC). On each occasion, following an overnight fast, subjects consumed one of 4 breakfast meals: Low GI-High Fiber (GI = 44, fiber = 20.4 g); Low GI-Low Fiber (GI = 43; fiber = 4.3 g); High GI-Low Fiber (GI = 70; fiber = 3.6 g); High GI-High Fiber (GI = 71; fiber = 20.3 g). Meals were equal in total kcal (∼600) and macronutrient composition (∼90g digestible carbohydrate; ∼21g protein; ∼16g fat). Brachial artery flow-mediated dilation (FMD) was performed pre-meal (∼8-9 AM), and 2h and 4h post-meal. RESULTS: ANOVA revealed a significant GI x time interaction (P=0.04). Postprandial FMD was increased significantly after the Low GI-High Fiber meal (14.5 + 1.2 (SEM)% at 4h vs. 7.3 + 1.9% pre-meal; P=0.003), with a trend for improved FMD after the Low GI-Low Fiber meal (11.4 + 1.1% at 4h vs. 8.2 + 1.0% pre-meal; P=0.17). Postprandial FMD was not affected by either the High GI-Low Fiber meal (8.9 + 1.3% at 4h vs. 9.9 + 3.4% pre-meal; P=0.67) or the High GI-High Fiber meal (10.0 + 1.6% at 4h vs. 10.0 + 2.1% pre-meal; P=0.98). CONCLUSIONS: In healthy adults, a meal low in GI and high in cereal fiber appears to improve postprandial endothelial function. A High-Fiber meal enhances endothelial function only if the meal is low in GI. Because the FMD response following the Low GI-Low Fiber meal was less than that following the Low GI-High Fiber meal, the full benefit of a Low-GI meal on postprandial endothelial function may be dependent in part on cereal fiber. Supported in part by NIH grant RR-00847 to the GCRC and a grant from the Grain Foods Foundation.