Impact Of Wheat Sprouts On Glucose And Insulin Metabolism

In an animal model, the intake of pregerminated brown rice was shown to produce lower postprandial glucose and insulin levels compared to white rice, and the authors ascribed this effect to the higher dietary fiber content of the pregerminated rice (Seki et al, 2005). The impact of dietary fiber on glucose and insulin metabolism is relatively well investigated. Intake of soluble fiber increases the viscosity of stomach and small intestine contents, thereby hindering carbohydrate digestion and absorption (Leclere et al, 1994). However, in population studies, intake of insoluble fiber, but not viscous fiber, has been associated with a decreased risk for type 2 diabetes or cardiovascular disease (Jenkins et al, 2000; Salmeron, Manson, et al. 1997). The mode of action of insoluble fiber in this connection remains unclear. As possible mechanisms of the positive effects of dietary fiber on hepatic glucose production, fermentation processes in the colon leading to the production of short-chain fatty acids and a decreased hepatic glucose output have been discussed (Thorburn et al, 1993).

In our study, consumption of a bread fortified with wheat sprouts revealed a glucose-lowering effect in the fasting as well as in the postprandial stage. This effect could not be observed after the intake of the bread fortified with imbibed wheat kernels. In contrast, plasma insulin levels of the subjects remained unchanged after intake of the bread fortified with wheat sprouts. The glucose-lowering effect is therefore likely to result from an improved peripheral insulin sensitivity, which may cause the improved glucose handling after a 9-day intake of the wheat bread fortified with wheat sprouts. This was confirmed by calculation of the homeostatic model assessment for insulin resistance in order to estimate the degree of insulin resistance. This calculation showed an increased insulin sensitivity after the intake of the bread fortified with wheat sprouts compared to the bread fortified with imbibed wheat kernels (Table 46.1).

Interestingly, Kim et al. (2006) showed that the naphthalenemethyl ester derivative of the phenolic compound dihydroxyhydrocinnamic acid was able to decrease blood glucose levels in streptozotocin-induced diabetic C57BL/6 mice and spontaneously diabetic ob/ob mice to near normoglycemia. In addition, this phenolic compound increased glucose uptake and enhanced phosphorylation of the insulin receptor-b subunit and insulin receptor substrate 1 in adipocytes in vitro and in vivo, which led to an increase in insulin receptor signaling. The hydroxycinnamic acid caffeic acid enhanced the glucose uptake into isolated adipocytes in a concentration-dependent manner (Hsu et al, 2000). This may in turn lead to an enhanced glucose utilization. Ferulic acid effectively suppressed blood glucose levels in streptozotocin-induced diabetic mice and in KK-Ay mice (Ohnishi et al., 2004).

In order to test whether ferulic acid is able to increase glucose uptake in insulin-sensitive adipocytes, murine 3T3-L1 adipocytes were incubated with or without insulin and/or ferulic acid. These experiments showed that ferulic acid positively affects glucose uptake in adipocytes in vitro (Figure 46.1).

In consideration of these results, it seems reasonable that the phenolic compounds in general and/or ferulic acid in particular in the wheat sprouts administered to humans in the o

TABLE 46.1 Impact of a Bread Fortified with Wheat Sprouts or Imbibed Wheat Kernels on Plasma Glucose, Insulin, and FFA Levels in Healthy Volunteers^^^^^^^^^^H^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^H^^^H

TABLE 46.1 Impact of a Bread Fortified with Wheat Sprouts or Imbibed Wheat Kernels on Plasma Glucose, Insulin, and FFA Levels in Healthy Volunteers^^^^^^^^^^H^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^H^^^H

0 min

30 min

60 min

120 min

180 min

Plasma glucose (mmol/l)

Before control bread period

4.6

± 0.08

7.2 ± 0.31

5.0 ± 0.20

4.5 ± 0.17

4.5 ± 0.17

After control bread period

4.4

± 0.09

7.5 ± 0.17

5.0 ± 0.22

4.5 ± 0.17

4.4 ± 0.09

Before experimental bread period

4.8

± 0.50

7.5 ± 1.12

5.4 ± 0.74

4.3 ± 0.74

4.4 ± 0.60

After experimental bread period

4.3

± 0.66**

6.5 ± 0.07**

4.7 ± 0.69**

4.2 ± 0.61

4.2 ± 0.38

Plasma insulin (mU/ml)

Before control bread period

4.7

± 0.47

31.6 ± 3.25

19.7 ± 2.32

11.7 ± 2.37

4.0 ± 0.85

After control bread period

1.9

± 0.20***

20.5 ± 2.50**

17.2 ± 2.50

6.5 ± 1.46

1.6 ± 0.24*'

Before experimental bread period

2.3

± 0.33

21.0 ± 1.95

18.3 ± 2.23

4.8 ± 1.32

2.3 ± 0.76

After experimental bread period

1.6

± 0.31

15.0 ± 2.41

15.5 ± 2.75

4.8 ± 1.22

2.0 ± 0.45

Plasma FFA (mmol/l)

Before control bread period

0.31

± 0.031

0.18 ± 0.024

0.07 ± 0.015

0.08 ± 0.020

0.29 ± 0.048

After control bread period

0.20

± 0.028***

0.13 ± 0.015

0.03 ± 0.009*

0.02 ± 0.007*

0.24 ± 0.046

Before experimental bread period

0.19

± 0.023

0.14 ± 0.017

0.03 ± 0.009

0.04 ± 0.07

0.21 ± 0.037

After experimental bread period

0.18

± 0.028

0.08 ± 0.012**

0.05 ± 0.009

0.04 ± 0.07

0.16 ± 0.037

HOMA-IR

Before control bread period

1.1

± 0.13

After control bread period

0.4

± 0.05***

Before experimental bread period

0.6

± 0.08

After experimental bread period

0.3

± 0.06

FFA, free fatty acid; HOMA-IR, homeostatic model assessment for insulin resistance. Source: Data from Andersen et al. (2008).

aMean fasting and postprandial plasma glucose, insulin, and FFA levels as well as mean HOMA-IR of the subjects before and after a daily intake of 300 g of a bread fortified with imbibed wheat kernels (control bread) for 9 days and before and after a daily intake of 300 g of a bread fortified with wheat sprouts (experimental bread). Data are given as mean ± SEM. Asterisks indicate a significant difference of the values before and after the respective diet (*p < 0.05, **p < 0.01; ***p < 0.001).

FFA, free fatty acid; HOMA-IR, homeostatic model assessment for insulin resistance. Source: Data from Andersen et al. (2008).

aMean fasting and postprandial plasma glucose, insulin, and FFA levels as well as mean HOMA-IR of the subjects before and after a daily intake of 300 g of a bread fortified with imbibed wheat kernels (control bread) for 9 days and before and after a daily intake of 300 g of a bread fortified with wheat sprouts (experimental bread). Data are given as mean ± SEM. Asterisks indicate a significant difference of the values before and after the respective diet (*p < 0.05, **p < 0.01; ***p < 0.001).

ro r

FIGURE 46.1

Ferulic acid affects glucose uptake in adipocytes. Uptake of the glucose analog 2-deoxyglucose in murine 3T3-L1 adipocytes after incubation with or without insulin (100 mg/ml) and/or ferulic acid (10 ng/ml). Data are given as percentage related to the untreated control (without insulin, without ferulic acid) ± SEM. Statistically significant differences are indicated.

FIGURE 46.1

Ferulic acid affects glucose uptake in adipocytes. Uptake of the glucose analog 2-deoxyglucose in murine 3T3-L1 adipocytes after incubation with or without insulin (100 mg/ml) and/or ferulic acid (10 ng/ml). Data are given as percentage related to the untreated control (without insulin, without ferulic acid) ± SEM. Statistically significant differences are indicated.

intervention trial presented here are responsible for the glucose-lowering effect through enhancement of glucose uptake by insulin-sensitive tissues. However, the exact biochemical mechanisms of this health benefit remain speculative.

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