Effects of Various Commercial Whole-Grain Breads on Postprandial Blood Glucose Response and Glycemic Index in Healthy Subjects

Research Article

Austin J Clin Med. 2018; 5(1): 1031.

Effects of Various Commercial Whole-Grain Breads on Postprandial Blood Glucose Response and Glycemic Index in Healthy Subjects

Lanzerstorfer P¹, Rechenmacher E², Lugmayr O¹, Stadlbauer V¹, Höglinger O¹, Vollmar A² and Weghuber J¹*

¹University of Applied Sciences Upper Austria, Stelzhamerstrasse, Austria

²Backaldrin GmbH, Kornspitzstrabe, Austria

*Corresponding author: Weghuber J, University of Applied Sciences Upper Austria, Stelzhamerstrasse 23, A-4600 Wels, Austria

Received: January 16, 2018; Accepted: February 08, 2018; Published: February 15, 2018


Postprandial hyperglycemia is a serious risk factor for cardiovascular disease and Type 2 Diabetes Mellitus (T2DM). As diet is a cornerstone of both T2DM prevention and therapy, we investigated the effects of various commercially available breads on postprandial glucose response and glycemic index. Furthermore, the impact of oilseed- and protein-enriched breads was evaluated, as well as the influence of different wheat flour coarseness settings. Three experiments were conducted to study the effects of various breads on the postprandial glucose levels of randomly selected subjects (42 in total). First, putative differences of seven types of commercially available whole-grain breads were studied. Second, the influence of oilseed- and protein-enriched breads was investigated and third, the influence of different wheat flour coarseness settings was characterized. The total Area Under Curve (AUC), postprandial glucose response, peak glucose level and glycemic index were calculated for each condition. Consumption of various types of whole-grain breads resulted in large variations in postprandial glucose response and significant differences in calculated glycemic indices. Furthermore, postprandial glucose levels and glycemic indices appeared significantly lower for protein-rich bread than compared to oil-seed-rich bread. Interestingly, no significant differences in postprandial glucose levels or glycemic indices were detected for fine, medium or coarse wheat flour breads. Based on the correlation study, breads with low total carbohydrates and high amounts of protein are advisable for the prevention of high glucose loads and should be considered by people suffering from T2DM. Trial Registration: O2413 (Ethics Commissions of Upper Austria).

Keywords: Glycemic index; Postprandial glucose response; Coarseness settings; Bread; Diabetes; Blood glucose levels


ANOVA: Analysis Of Variance; AUC: Area under the Curve; GI: Glycemic Index; T2DM: Type 2 Diabetes Mellitus


Bread is one of the most important staple foods worldwide [1]. Therefore, it represents a major source of carbohydrates and, thus, energy in human nutrition, especially in Western civilization. Carbohydrates are key modulators and the main determinants of postprandial glucose response, as the ingestion of carbohydrates is accompanied by an increase in blood glucose levels [2,3]. Carbohydrate-rich foods are classified into three Glycemic Index (GI) categories based on their effect on postprandial glucose response (low <55, medium 55-69 and high <70) [4]. The ingestion of high-GI foods causes excessive postprandial glucose levels and can trigger a disproportionately high insulin response, which is associated with insulin resistance, hyperinsulinemia and, ultimately, the development of Type 2 Diabetes Mellitus (T2DM) [5]. On the contrary, low-GI foods are thought to cause moderate increases in blood glucose concentrations [5]. To prevent increased blood glucose loads, carbohydrates should be predominantly composed of starches, with reduced amounts of mono- and disaccharides. With respect to T2DM, foods and diets should be energy controlled and low GI. In this context, lower GI breads are of particular interest, especially in regions that consume large amounts of bread (e.g., US, Europe) [3]. In recent years, several strategies and approaches to attenuating the GI of bread have appeared, including the inclusion of ingredients with healthful properties. This includes the addition of viscous and non-viscous fibers, legume flours, fruit-based ingredients, specific functional micronutrients and enrichment with intact structures not accessible to human amylase [6-8].

Unfortunately, nutritional characterization of various commercially available breads, including white, whole-meal and seeded breads, has indicated high glycemic properties [9]. However, breads rich in intact grain kernels, oat bran and natural fibers (e.g., beta glucans) have been reported to improve glycemic control and insulin sensitivity [9-11]. Furthermore, they promote satiety via slowed gastric emptying. The ingestion of whole-grain foods in particular has been associated with lower risks of T2DM, cardiovascular disease and weight gain [12,13].

The aims of this study were to i) examine the postprandial glycemic response and GI of seven commercially available whole-grain breads (with white bread as the reference), ii) investigate the influence of fat and protein via oilseed- and protein-enriched breads on postprandial glucose response and GI, and iii) evaluate the role of flour coarseness (fine, medium and coarse) on the selected nutritional parameters.

Materials and Methods

5.1. Study design

The study protocols were approved by the Ethics Commission of Upper Austria (trial number O2413). In total, 42 men (14) and women (28) were included in the study. Study subjects were healthy people of normal weight (mean BMI of 22.5 ± 3.0), with a mean age of 28.1 ± 7.2 years. All study participants provided written informed consent. The first experiment consisted of 15 female and 9 male subjects, the second of 7 female and 1 male subjects and the third of 7 female and 3 male participants. Study subjects were urged to observe the following conditions: Abstention from i) alcohol, ii) fiber-rich foods, iii) medicines, iv) dietary supplements, v) excessive physical exercise and vi) smoking for at least 24 hours prior to each study day. Furthermore, the participants were encouraged not to eat or drink anything except water or unsweetened tea for ten hours before measuring fasting plasma blood glucose levels. Fasting blood samples were collected prior the consumption of the respective test breads (empty stomach). Each test meal was designed to contain 50g available carbohydrates from the test bread ingested over a period of 15min. White bread was used as the reference food. Each subject was served 250mL of drinking water. Blood samples were collected 15, 30, 45, 60, 90 and 120 minutes after bread consumption. The time interval between testing different breads was at least three days.

5.2. Test breads

All test breads were provided by backaldrin GmbH (Asten, Austria). In total, 9 different commercial whole-grain breads were studied in addition to the white bread reference: 1) whole-grain rolls, 2) multi-seed whole-grain bread, 3) whole-grain spelt bread, 4) whole-grain rye bread, 5) whole-grain mixed rye bread, 6) whole-grain oat bread, 7) whole-grain wheat bread, 8) oilseed bread and 9) protein bread. Detailed information about the main ingredients is given in Table 1. Furthermore, the nutrient composition results, as well as the sieve analysis of different coarseness settings, of the tested breads are shown in Tables 2, 3.