Abstract
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.
Highlights
Postprandial hyperglycemia is a risk factor for cardiovascular disease (CVD) even among apparently healthy adults without diabetes [1,2], and is a better predictor of mortality from all causes and CVD than is fasting blood glucose [3]
In healthy men and women, consumption of a breakfast meal that is high in cereal fiber (20 g; 16–18 g of wheat bran) and low in glycemic index (GI) significantly improved flow-mediated dilation (FMD) 4 h after ingestion
Our data show that it is the combination of high cereal fiber and low GI that produced this beneficial effect on postprandial FMD, whereas a low-GI meal that is low in cereal fiber, and a high-GI meal that is high in cereal fiber, did not
Summary
Postprandial hyperglycemia is a risk factor for cardiovascular disease (CVD) even among apparently healthy adults without diabetes [1,2], and is a better predictor of mortality from all causes and CVD than is fasting blood glucose [3]. Brachial artery flow-mediated dilation (FMD) is the most widely used non-invasive technique to assess endothelial function in humans [8], and a meta-analysis demonstrated that impairment in brachial artery FMD is significantly associated with future cardiovascular morbidity and mortality [9]. Most of the evidence demonstrating hyperglycemia-associated impairment in FMD comes from studies using oral glucose tolerance tests [4]. Such tests may not adequately reflect postprandial glucose
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