Both glycemic index and dietary fiber are associated with cardiovascular disease risk, which may be related in part to postprandial vascular effects. We examined the effects of both glycemic index (GI) and dietary (mainly cereal) fiber on postprandial endothelial function. Eleven adults (5 men; 6 women; age = 42.4 ± 16.1 years; weight = 70.5 ± 10.7 kg; height = 173.7 ± 8.7 cm) consumed four different breakfast meals on separate, randomized occasions: High-Fiber, Low-GI (HF-LGI: Fiber = 20.4 g; GI = 44); Low-Fiber, Low-GI (LF-LGI: Fiber = 4.3 g; GI = 43); Low-Fiber, High-GI (LF-HGI: Fiber = 3.6 g; GI = 70); High-Fiber, High-GI (HF-HGI: Fiber = 20.3 g; GI = 71). Meals were equal in total kcal (~600) and macronutrient composition (~90 g digestible carbohydrate; ~21 g protein; ~15 g fat). The HF-LGI meal resulted in a significant increase in flow-mediated dilation (FMD) 4 h after meal ingestion (7.8% ± 5.9% to 13.2% ± 5.5%; p
= 0.02). FMD was not changed after the other meals. Regardless of fiber content, low-GI meals resulted in ~9% lower 4-h glucose area under curve (AUC) (p
< 0.05). The HF-LGI meal produced the lowest 4-h insulin AUC, which was ~43% lower than LF-HGI and HF-HGI (p
< 0.001), and 28% lower than LF-LGI (p
= 0.02). We conclude that in healthy adults, a meal with low GI and high in cereal fiber enhances postprandial endothelial function. Although the effect of a low-GI meal on reducing postprandial glucose AUC was independent of fiber, the effect of a low-GI meal on reducing postprandial insulin AUC was augmented by cereal fiber.
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