EFFECT OF WHEAT BRAN ON POSTPRANDIAL GLUCOSE RESPONSE IN SUBJECTS WITH IMPAIRED FASTING GLUCOSE

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1 CURRENT TOP OPICS IN NUTRACEUTICAL RESEARCH Vol. ol. 9, No. o. 1/2, pp , 2011 ISSN print, Copyright 2011 by New Century Health Publishers, LLC All rights of reproduction in any form reserved EFFECT OF WHEAT BRAN ON POSTPRANDIAL GLUCOSE RESPONSE IN SUBJECTS WITH IMPAIRED FASTING GLUCOSE A. Afaghi, B. Ranjbari Omidi, M. Sarreshtehdari, L. Ghanei, M. Alipour, A. Azadmehr, M. Emam Jomeh and A. Safari-Varyani Qazvin Metabolic Disease Center, Qazvin University of Medical Science, Qazvin, Iran [Received February 17, 2011; Accepted May 9, 2011] ABSTRACT: In addition to long term effect of wheat bran on improvement of insulin sensitivity, its effect on the postprandial blood glucose response, in clinical implementation is important. Therefore the aim of this study was to measure the reduced postprandial blood glucose of impaired fasting blood glucose subjects following consuming high glycemic load (GL) meal containing 25 g wheat bran. Nine subjects were given each of the following 2 meals in a randomized order one week apart: a high-gl meal (control), and the same high GL meal plus wheat bran (test meal). Using glucometer, finger prick blood samples for glucose analysis were used before the meals (fasting) and at 30, 60, 90, and 120 min following the meal ingestion. At 90 and 120 min after the test meal ingestion, there was a 10.3% and 11% reduction in blood glucose concentration compared with control meal (P = 0.02, and 0.03 respectively). Also, there was positive correlation between 2 hrs postprandial blood glucose concentration of control and test meals (r = 0.95, P < at 0.01 level). The repeated measures ANOVA, test of within-subjects effects, confirmed that the blood glucose profile over time differed between the 2 meal types (P < 0.03; n = 9, for the group by time interaction). KEY WORDS: Impaired fasting blood glucose,postprandial blood glucose, Wheat bran Corresponding Author: Dr. B. Ranjbari Omidi, Qazvin Metabolic Disease Center, Qazvin University of Medical Science, Qazvin, Iran; FAX: Fax: ; aafa2000@gmail.com Introduction Dietary fibers (DFs) influence the digestion and absorption rate of carbohydrates and thus the blood glucose response (Schulze et al., 2004). DFs are available in two types of soluble and insoluble (Martin and Andreas, 2008). Soluble DFs have viscous and gel-forming characteristics (i.e., pectin, inulin, and ß-glucans), inhibit macronutrient absorption and reduce postprandial glucose response (Schulze et al., 2007). Soluble DFs also do colonic fermentation which leads to production of short-chain fatty acids such as acetate, propionate, and butyrate and consequently reducing hepatic glucose output (Schulze et al., 2007). However in prospective cohort studies, there was not strong association between soluble DFs and reduced diabetic risk (De Munter et al., 2007; Schulze et al., 2007). Insoluble DFs (i.e., cellulose and hemicelluloses) lower glycemic index of foods. Fiber-rich foods generally have a low glycemic index affecting on postprandial glucose (Riccardi et al., 2008), hence, there is negative correlation between dietary glycemic index and total DFs (Yin et al., 2009). In several studies beneficial effect of insoluble DFs in long term has been reported. Whole grain consumption was inversely associated with newly detected abnormal glucose metabolism and type 2 diabetes. (Salmeron et al., 1997 a; Salmeron et al., 1997 b; Meyer et al., 2000; Stevens et al., 2002). These findings suggest that consumption insoluble DFs contributes to a number of metabolic effects including improvement of insulin sensitivity. Choice of carbohydrate-rich foods with high glycemic index in the habitual diet was associated with an increased risk of diabetes (Schulze et al., 2004). So, consuming wheat bran along with high glycemic load meal may modify GI of meal and affecting on digestion rate, reducing glycemic index and load of ingested meal and consequently suppressing postprandial blood glucose. In addition to long term effect of whole grain and wheat bran on glucose metabolism, its clinical implementation on controlling elevated blood glucose concentration of impaired glucose tolerance (IFG) of subjects is important. Dose-response effect of fiber on postprandial glucose response has been demonstrated in previous studies. In a study it was demonstrated that, the higher the fiber amount in ingested meal, the lower the glycemic index of meal (Yin et al., 2009), and the lower the glycemic index, the weaker the blood glucose respond (Afaghi et al., 2007). In addition previous study showed that small amount of fiber doesn t significantly effect on blood glucose response (Jenkins

2 36 Wheat bran and glucose response et al., 2002). That was rational for choosing the amount of 1- tablespoon (25 g) wheat bran in test meal in current study IFG is now defined by an elevated fasting plasma glucose (FPG) concentration (e 100 FPG <126 mg/dl) (Granfeldt et al., 2006)). Impaired glucose tolerance (IGT) is defined by an elevated 2-h plasma glucose concentration (e 140 IGT <200 mg/dl) after a 75-g glucose load on the oral glucose tolerance test (OGTT) in the presence of an FPG concentration <126 mg/dl (Pereira et al., 2002; Granfeldt et al., 2006). The prevalence of IFG and IGT in different populations varied between 2-17% and % respectively and current estimates indicate that most individuals (perhaps up to 70%) with these metabolic abnormalities eventually develop diabetes (Unwin, 2002). These metabolic abnormalities especially among gestational diabetes mellitus patients are health problems and these patients may resist using medication for blood glucose control. Therefore, to investigate the role of insoluble DF on postprandial blood glucose, we explored the effect of high glycemic load rice meal along with wheat bran on postprandial blood glucose of IFG subjects. MATERIALS AND METHODS Nine impaired fasting glucose (124 > FBS > 100 mg/d, aged years, and BMI = kg/m 2, subjects were recruited from Endocrine Clinic. Subjects were excluded if they had significant medical condition or used prescribed medication (including blood glucose lowering agents). The study was approved by the Human Research Ethics Committee of Qazvin University of Medical Science and subjects were given information sheet and provided consent before participation. The research was supported by Qazvin University s Doctoral students research budget. The subjects were given each of the following 2 meals in a randomized order one week apart: a high-gl meal (control meal), and the same high-gl meal plus wheat bran (test meal). On the testing day, the subjects were fasted for 12 hrs before the mid day meal. The subjects ate their meals in 20 min. Finger prick blood samples for glucose analysis (with the use of a glucometer, Medisense Optium; Abott Laboratories, MediSense Products, Bedford, MD) were collected before the meal (baseline) and at 30, 60, 90, and 120 min after the meals. Standard isocaloric meals (765 kcal; 23% of energy as protein, 30% of energy as fat, and 47% of energy as carbohydrate) included 200 g Basmati steamed rice, 100 g back strip meat (kebab), 2 medium tomatoes, 100 g yoghurt and 20 g butter was ingested in both control and test day. The rice was low GI (Basmati, GI = 50) (Foster-Powell et al., 2002). The GL was calculated as (GI/100) X g available carbohydrate which was 42 for each meal. The test meal included 25 g fine wheat bran (Dineh Company, Tehran Iran) which was consumed mixed with yoghurt. Nutritional composition of meal demonstrated in table 1 using Food Works analysis software, version 6 (Xyris, 2009). STATISTICS The sample size was calculated based on effect sizes obtained for glycemic index powered at 90% and an alpha of 5% in an intervention study of glycemic index of foods (Jenkins et al., 1981). We estimated that an effect size of 2.5 and a calculated sample size of 9 were appropriate for our study. Data were inspected for normality of distribution before use of parametric statistics with SPSS version 16 (SPSS Inc, Cary, NC). Data are reported as means ± SD. The blood glucose response was analyzed by using the area under the curve (AUC) and paired samples t test. The repeated-measures ANOVA was used to test for the effect of meal type, time post meal, and their interaction on blood glucose measured at baseline and at 30, 60, 90, and 120-min intervals after eating the meal. Pearson correlation analysis performed to find out the correlation between 2 hrs post control and test meal glucose response. TABLE 1. Nutritional composition of control and test meals 1. 1 FoodWorks analysis software, 2009, version 6; 2 Glycemic index; 3 Glycemic load, Extracted from international table of glycemic index and glycemic load (Foster-Powell et al., 2002) Ingredient Control Test meal Carbohydrate Protein Fat EnergyKcal GI 2 GL 3 Weight (g) Steamed Basmati rice Meat (kebab) Butter Tomato (2 small) Yoghurt Total fiber 2 (0) 27 (27) (wheat bran) Total FIGURE 1. Comparison of blood glucose response between the control meal and the test meal containing wheat bran

3 Wheat bran and glucose response 37 RESULTS DISCUSSION Eight females and one male subject (aged 38 ± 12 years, BMI 24 ± 2 kg/m2) completed the study. The blood glucose at baseline (zero time) before the test meal was similar to that for control meal (P = 0.6). The blood glucose responses to both the control and test meals are shown in table 2 and figure 1. Blood glucose rose to a peak at 40 min after meals ingestion, followed by a steady decrease. The blood glucose response to wheat bran started at 40 min after the meals ingestion. At 60 min there was 5.5% reduction in blood glucose concentration of test meal. However the effect of wheat bran on blood glucose was significant at 90 and 120 min after the test meal ingestion which resulted in 10.3% and 11% reduction of blood glucose compared with control meal (P = 0.02, and 0.03 respectively). As figure 2 shows, there was positive correlation between elevated 2 hrs postprandial blood glucose in control and test meals (r = 0.95, P < at 0.01 level). The repeated measures ANOVA, test of within-subjects effects, confirmed that the blood glucose profile over time differed between the 2 meal types (P < 0.03; n = 9 for the group by time interaction). Although, AUC was greater for the control meal ( ± ) than for test meal ( ± ), but, the differences was not significant (Paired-samples t test, P = 0.3) (table 2). TABLE 2. Comparison of blood glucose response between the control meal and the test meal. Time (min) after the Control meal Test meal Changes% P meal ingestion (mg/dl) (mg/dl) Baseline (0) ± ± ± ± ± ± ± ± ± ± Area under the curve (AUC) ± ± FIGURE 2. Correlation between 2 hrs blood glucose responses after control and test meals Current study investigated the effect of wheat bran on postprandial blood glucose level after ingestion of a high glycemic load meal. Our study demonstrated that ingestion of 25 g (one table spoon) of wheat bran in one occasion with main meal containing 765 kcal energy, 357 g carbohydrate and GL of 42 resulted in significant reduction of postprandial blood glucose response at 90 and 120 min following the ingestion of the meal. Blood glucose concentration of control meal at 90 min (154.3 ± 49.9) and 120 min (146.7 ± 50.1) significantly reduced to ± 37.1 and ± 34.4 after ingestion of test meal which showed a blood glucose reduction of 10.3% and 11% respectively. And there was correlation between 2 hrs postprandial blood glucose concentrations of control and test meals. This correlation indicated that wheat bran ingestion lowers blood glucose response compared to control meal. Our high glycemic load control meal (GL = 42) increased 2-hrs blood glucose level (146.7 ± 50.1), while adding wheat bran to the meal caused clinically significant reduction (128.9 ± 34.4) of postprandial blood glucose. Meals with a GL > 20 are considered to be high, and over a day a GL of 120 is rated as high (Brand-Miller, 2005). Hence, the GL of the meals in our study was 2 times higher than the GL most persons would consume in a meal. Regular consumption of meals with such a high GL would not be suitable for persons with IGT or diabetes and ingestion of such a meal with wheat bran reduces glycemic index and glycemic load of the meal and consequently postprandial blood glucose (Afaghi et al., 2007). In a study conducted by Jenkins (Jenkins et al., 2002) administration of 19 g fiber in daily diet (high wheat bran bread and breakfast cereal) compared to control diet having 4 g fiber per day did not significantly change fasting blood glucose or HbA1c concentration over 3 months intervention. In this study total amount of 19 g fiber was consumed entire the day, while our subjects ingested 25 g fiber in single does. We think amount of fiber in Jenkins study was not enough to effect on glycemic control. Dose-response effect of fiber on postprandial glucose concentration has been demonstrated. There was negative correlation between dietary glycemic index and ingested total diet fiber (Yin et al., 2009), and lower the glycemic index, the weaker the blood glucose response (Afaghi et al., 2007). In addition, Zhang and colleagues (Zhang et al., 2006) in their prospective cohort study demonstrated that each 10 g/day increase in total fiber intake was associated with 26% reduction in risk of GDM and each 5-g/day increment in cereal and fruit fiber was associated with a 23% and 26% reduction of GDM risk respectively. Moreover, from epidemiological studies, it has been reported that a diet based on carbohydrate rich-foods

4 38 Wheat bran and glucose response with a low-gi, high fiber content may prevent diabetes and cardiovascular disease (Riccardi et al., 2008). The amount of 25 g bran fiber was rational and enough to reduce glycemic index of high GL meal, while it is somewhat palatable. In practice due to limited palatability and also produced flatus by insoluble DF, consumption of large amount of fiber is not pleasure and cause discomfort for diabetes subjects. Irrespective of long term effect of wheat bran on glycemic control, considering that lowering effect of wheat bran on postprandial blood glucose level is a non-invasive nutritional intervention, it may have many implementations. A large number of IGT patients may resist to medication intake. IGT is observed in gestation diabetes mellitus in which there is restriction for blood glucose lowering medication intake and also mothers may resist for insulin injection therapy. Consumption of wheat bran along with carbohydrate-rich choices meal can provide suitable source of energy for these mothers. REFERENCES Afaghi, A., O Connor, H. and Chow, C. M. (2007) Highglycemic-index carbohydrate meals shorten sleep onset. American Journal of Clinical Nutrition 85, Brand-Miller, J. C. (2005)) Home of the glycemic index, glycemic load. Internet: (accessed 20 December 2005). De Munter, J. S., Hu, F. B., Spiegelman, D., Franz, M. and Van Dam, R. M. (2007) Whole grain, bran, and germ intake and risk of type 2 diabetes: a prospective cohort study and systematic review. Public Library of Science, PLoS Medicine 4, e261. Foster-Powell, K., Holt, S. H. and Brand-Miller, J. C. (2002) International table of glycemic index and glycemic load. American Journal of Clinical Nutrition 76, Granfeldt, Y., Wu, X. and Bjorck, I. (2006) Determination of glycemic index ; some methodological aspects related to the analysis of carbohydrate load and charactristics of the previous meal. European Journal of Clinical Nutrition 60, Jenkins, D. J., Wolever, T. M., Taylor, R. H., Barker, H., Fielden, H., Baldwin, J. M., Bowling, A. C., Newman, H. C., Jenkins, A. L. and Goff, D. V. (1981) Glycemic index of foods: a physiological basis for carbohydrate exchange. American Journal of Clinical Nutrition 34, Jenkins, D. J. A., Kendall, C. W. C., Augustin, L. S. A., Martini, M. C., Axelsen, M., Faulkner, D., Vidgen, E., Parker, T., Lau, H., Connelly, P. W., Teitel, J., Singer, W., Vandenbroucke, A. C., Leiter, L. A. and Josse, R. G. (2002) Effect of Wheat Bran on Glycemic Control and Risk Factors for Cardiovascular Disease in Type 2 Diabetes. Diabetes Care 25, Martin, Q. W. and Andreas, F. H. P. (2008) Metabolic effects of dietary fiber consumption and prevention of diabetes. Journal of Nutrition 138, Meyer, K. A., Kushi, L. H., Jacobs DR, J., Slavin, J., Sellers, T. A. and Folsom, A. R. (2000) Carbohydrates, dietary fiber and incidence of type 2 diabetes in older women. American Journal of Clinical Nutrition 71, Pereira, M., A., Jacobs, D., R., Jr Pins J., J., Raatz, S., K., Gross, M., D., Slavin, J., L. and Seaquist, E., R. (2002) Effect of whole grains on insulin sensitivity in overweight hyperinsulinemic adults. American Journal of Clinical Nutrition 75: Riccardi, G., Rivellese, A. A. and Giacco, R. (2008) Role of glycemic index and glycemic load in the healthy state, in prediabetes, and in diabetes. American Journal of Clinical Nutrition 87, 269S-274. Salmeron, J., Ascherio, A. and Rimm, E. B. (1997 a) Dietary fiber, glycemic load, and risk of NIDDM in men. Diabetes Care 20: Salmeron, J., Manson, J. E., Stampfer, M. J., Colditz, G. A., Wing, A. L. and Willett, W. C. (1997 b) Dietary fiber, glycemic load, and risk of non-insulin-dependent diabetes mellitus in women. The Journal of the American Medical Association 277: Schulze, M., Schulze, M., Heidmann, C. and Schienkiewitz, A. (2007) Fiber and Magnesium intake and incidence of Type 2 diabetes: A prospective study and meta analysis. Archives of Internal Medicine 167, Schulze, M. B., Liu, S., Rimm, E. B., Manson, J. E., Willett, W. C. and Hu, F. B. (2004) Glycemic index, glycemic load, and dietary fiber intake and incidence of type 2 diabetes in younger and middle-aged women. American Journal of Clinical Nutrition 80, Stevens, J., Ahn, K., Houston, D., Steffan, L. and Couper, D. (2002) Dietary fiber intake and glycemic index and incidence of diabetes in African-American and white adults: the ARIC study. Diabetes Care 25, Unwin, N. (2002) International diabetes fedration IGT/ IFG consensus statement. Diabetes UK. Diabetes Medicine 19, Xyris. (2009)) Trusted Australian software for nutrient analysis. Yin, W., Huang, C. and Zheng W, L. L. (2009) Associations

5 Wheat bran and glucose response 39 between glucose response and dietary fiber intakes in patients with DM. Wei Sheng Yan Jiu 38, (abstract). Zhang, C., Liu, S., Solomon, C. G. and Hu, F. B. (2006) Dietary Fiber Intake, Dietary Glycemic Load, and the Risk for Gestational Diabetes Mellitus. Diabetes Care 29,

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