Effects of Glycemic Index and Cereal Fiber on Postprandial Endothelial Function, Glycemia, and Insulinemia in Healthy Adults

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 hours 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-hour glucose area under curve (AUC) (p < 0.05). The HF-LGI meal produced the lowest 4-hour 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.

Keywords: cardiovascular disease; flow-mediated dilation; glucose; insoluble fiber; insulin; vascular.

Figure 1

Postprandial change in flow-mediated dilation (FMD) across 4 h for each meal. Dashed lines represent responses for each individual. Solid lines represent mean responses (± SD). FMD was not different across time points for all meals except High-Fiber, Low-GI at 4 h compared to baseline (p = 0.021; Bonferroni adjusted p = 0.165).

Figure 2

Glucose concentrations over time in response to four meals differing in glycemic index (GI) and fiber content. Dashed lines represent individual subject responses. Solid lines represent mean responses for all subjects. See text and Table 2 for statistical comparisons.

Figure 3

Glycemic response as area under curve (AUC) over 4 h in response to four meals differing in glycemic index (GI) and fiber content. Boxes for each meal represent the interquartile range. Minimum and maximum values are indicated at the tips of each vertical line. The median for each meal is depicted by the horizontal line within each box. See Table 3 for statistical comparisons between meals.

Figure 4

Insulin responses to four meals differing in glycemic index (GI) and dietary fiber content. Dashed lines represent individual subject responses. Solid lines represent mean responses for all subjects. See text and Table 4 for statistical comparisons between meals.

Figure 5

Plasma insulin area under curve (AUC) over 4 h in response to four meals differing in glycemic index (GI) and fiber content. Boxes for each meal represent the interquartile range. Minimum and maximum values are indicated at the tips of each vertical line. The median for each meal is depicted by the horizontal line within each box. See Table 5 for statistical comparisons between meals.