Insoluble fiber in young barley leaf suppresses the increment of postprandial blood glucose level by increasing the digesta viscosity

Abstract

Barley (Hordeum vulgare L.) is a well-known cereal plant. Young barley leaf is consumed as a popular green-colored drink, which is named "Aojiru" in Japan. We examined the effects of barley leaf powder (BLP) and insoluble fibers derived from BLP on postprandial blood glucose in rats and healthy Japanese volunteers. BLP and insoluble fibers derived from BLP suppressed the increment of postprandial blood glucose levels in rats (P < 0.01), and increased the viscosity of their digesta. The insoluble fibers present in BLP might play a role in controlling blood glucose level by increasing digesta viscosity. In human, BLP suppressed the increment of postprandial blood glucose level only in those which exhibited higher blood glucose levels after meals (P < 0.01). BLP might suppress the increment of postprandial blood glucose level by increasing digesta viscosity in both of rats and humans who require blood glucose monitoring.

Figure 1

Preparation flow for the water-EtOH soluble and insoluble fractions of BLP.

Figure 2

Oral sucrose tolerance test for dose finding of BLP. The delta blood glucose levels in rats at 0–120 minutes after oral administration of 2,000 mg/kg of sucrose with no BLP (control), 500 mg/kg, and 1,500 mg/kg of BLP were measured. Each data point represents mean ± SEM (n = 6). A significant interaction was found between the effect of dose and time after administration (P < 0.01, 2-way ANOVA). Delta blood glucose levels without a common letter differ (P < 0.05, multiple comparisons).

Figure 3

Oral sucrose tolerance test with the water-EtOH soluble and insoluble fractions of BLP. The delta blood glucose levels in rats at 0–120 minutes after oral administration of 2,000 mg/kg of sucrose with no BLP (control), 1,500 mg/kg of BLP, 384 mg/kg of the soluble fraction, and 1,100 mg/kg of the insoluble fraction were measured. Each data point represents mean ± SEM, for n = 14 (control, BLP, and soluble fraction) and n = 13 (insoluble fraction). A significant interaction was found between the effects of the different fractions and the time after administration (P < 0.001, 2-way ANOVA). Delta blood glucose levels without a common letter differ (P < 0.05, multiple comparisons).

Figure 4

The coefficient of viscosity of (a) gastric contents, (b) small intestinal contents, and (c) cecal contents in rats after administration of no fiber diet (control in the panel), BLP containing diet (BLP in the panel), and BLP-derived insoluble fiber-containing diet (insoluble fiber in the panel). Each data point represents the mean for n = 3. Significant differences were found between the coefficients of viscosity of the small intestinal and cecal contents among the groups (P < 0.05, ANCOVA). Coefficients of viscosity for gastrointestinal digesta without a common letter differ (P < 0.05, multiple comparisons).

Figure 5

The coefficient of viscosity of control artificial digesta (control), artificial digesta containing BLP (BLP in the panel), and insoluble fiber derived from BLP (insoluble fiber in the panel), before infusion into the small intestine in rats. Significant differences were found between the coefficients of viscosity of the artificial digesta among groups (P < 0.01, ANCOVA). The coefficients of viscosity of artificial digesta without a common letter differ (P < 0.05, multiple comparisons).

Figure 6

Catheterization test of artificial digesta. (a) The delta blood glucose levels in rats at 0–120 minutes. (b) The delta insulin levels in rats at 0–60 minutes, after small intestinal infusion of the control, BLP-containing (BLP in the panel), and BLP-derived insoluble fiber-containing artificial digesta (insoluble in the panel) were measured. Each data point represents the mean ± SEM for n = 4 (control and insoluble fiber) and n = 3 (BLP). A significant interaction was found between the effects of addition and time after administration (P < 0.05, multiple comparisons). Delta blood glucose levels without a common letter differ (P < 0.05, multiple comparisons).

Figure 7

The delta blood glucose levels in humans at 0–120 minutes after administration of 200 g of rice with 0 g (control in the panel) and 1.5 g of BLP (BLP in the panel). The high glucose group (n = 12) is composed of subjects whose levels were above the blood glucose level means between 0 and30 minutes after placebo administration. Similarly, the low glucose group (n = 21) is composed of those whose levels were below the blood glucose level means between 0 and 30 minutes after placebo administration. Each data point represents mean ± SEM. A significant 3-way interaction was found among the effects of BLP, time after administration, and glucose level (P < 0.05, 3-way ANOVA). Delta blood glucose levels without a common letter differ (P < 0.05, multiple comparisons).