Advertisement
Browse Subject Areas
?

Click through the PLOS taxonomy to find articles in your field.

For more information about PLOS Subject Areas, click here.

  • Loading metrics

Open Access

Peer-reviewed

Research Article

Effects of Unfermented and Fermented Whole Grain Rye Crisp Breads Served as Part of a Standardized Breakfast, on Appetite and Postprandial Glucose and Insulin Responses: A Randomized Cross-over Trial

  • Daniel P Johansson ,

    daniel.p.johansson@slu.se

    Affiliation Department of Food Science, BioCenter, Swedish University of Agricultural Sciences (SLU), Uppsala, Sweden

    ⨯
  • Isabella Lee,

    Affiliation Department of Food Science, BioCenter, Swedish University of Agricultural Sciences (SLU), Uppsala, Sweden

    ⨯
  • Ulf Risérus,

    Affiliation Department of Public Health and Caring Sciences, Clinical Nutrition and Metabolism, Uppsala University, Uppsala, Sweden

    ⨯
  • Maud Langton,

    Affiliation Department of Food Science, BioCenter, Swedish University of Agricultural Sciences (SLU), Uppsala, Sweden

    ⨯
  • Rikard Landberg

    Affiliations Department of Food Science, BioCenter, Swedish University of Agricultural Sciences (SLU), Uppsala, Sweden, Nutritional Epidemiology Unit, Institute of Environmental Medicine, Karolinska Insitutet, Stockholm, Sweden

    ⨯

Abstract

Background

Whole grain rye products have been shown to increase satiety and elicit lower postprandial insulin response without a corresponding change in glucose response compared with soft refined wheat bread. The underlying mechanisms for these effects have not been fully determined The primary aim of the study was to investigate if whole grain rye crisp bread compared to refined wheat crisp bread, elected beneficial effects on appetite and postprandial insulin response, similarly as for other rye products.

Methods

In a randomized cross-over trial, 23 healthy volunteers, aged 27-70 years, BMI 18-31.4 kg/m2, were served a standardized breakfast with unfermented whole grain rye crisp bread (uRCB), fermented whole grain rye crisp bread (RCB) or refined wheat crisp bread (WCB), Appetite was measured using a visual analogue scale (VAS) until 4 h after breakfast. Postprandial glucose and insulin were measured at 0-230 min. Breads were chemically characterized including macronutrients, energy, dietary fiber components, and amino acid composition, and microstructure was characterized with light microscopy.

Results

Reported fullness was 16% higher (P<0.001), and hunger 11% and 12% lower (P<0.05) after ingestion of uRCB and RCB, respectively, compared with WCB. Postprandial glucose response did not differ significantly between treatments. Postprandial insulin was 10% lower (P<0.007) between 0-120 min but not significantly lower between 0-230 min for RCB compared with WCB. uRCB induced 13% (P<0.002) and 17% (P<0.001) lower postprandial insulin response between 0-230 min compared with RCB and WCB respectively.

Conclusion

Whole grain rye crisp bread induces higher satiety and lower insulin response compared with refined wheat crisp bread. Microstructural characteristics, dietary fiber content and composition are probable contributors to the increased satiety after ingestion of rye crisp breads. Higher insulin secretion after ingestion of RCB and WCB compared with uRCB may be due to differences in fiber content and composition, and higher availability of insulinogenic branched chain amino acids.

Trial Registration

ClinicalTrials.gov NCT02011217

Citation: Johansson DP, Lee I, Risérus U, Langton M, Landberg R (2015) Effects of Unfermented and Fermented Whole Grain Rye Crisp Breads Served as Part of a Standardized Breakfast, on Appetite and Postprandial Glucose and Insulin Responses: A Randomized Cross-over Trial. PLoS ONE 10(3): e0122241. https://doi.org/10.1371/journal.pone.0122241

Academic Editor: Neil M. Johannsen, Louisiana State University, UNITED STATES

Received: June 16, 2014; Accepted: February 10, 2015; Published: March 31, 2015

Copyright: © 2015 Johansson et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited

Data Availability: All relevant data are within the paper and its Supporting Information files.

Funding: RL holds a research grant from Barilla for the financing of the current study (http://www.barillagroup.com/). RL did not get salary or any other financial compensation for conducting the present study or for any other purposes. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing interests: DPJ has read the journal's policy and the authors of this manuscript have the following competing interests: RL holds a research grant from Barilla for the financing of the current study. RL did not get salary or any other financial compensation for conducting the present study or for any other purposes. No other financial competing interests exist.

Introduction

Obesity and overweight are becoming more prevalent and causing increasing concern in large parts of the world [1]. Lifestyle factors such as low physical activity and poor diet are strong contributors to the development of obesity and its related diseases and are therefore important targets in the prevention and treatment of these conditions [2,3]. One approach is to reduce the overall energy intake by increasing the feeling of fullness and reducing hunger through tailored foods [4]. This is however complex, since appetite is controlled by both psychological factors and physiological responses related to food properties such as composition, energy density, and microstructure [5].

Products based on whole grain rye, mainly porridge and soft bread, have repeatedly been shown to induce higher subjective satiety [6–13] and lower postprandial insulin secretion with- or without corresponding difference in postprandial glucose profile [10,12–16] compared with refined wheat bread. Lower postprandial insulin response may increase insulin sensitivity and decrease low-grade inflammation and is therefore most likely beneficial for the prevention of Type 2 diabetes [17,18]. Several studies have attempted to explain the phenomenon of lower postprandial insulin responses without lower glucose responses, but it has not yet been fully explained. Specific features of rye products, such as dense structure and the formation of an amylose layer surrounding the starch granules [15], as well as certain phenolic acids found in some rye varieties [10], have been suggested as important for the beneficial postprandial insulin response. Furthermore, some amino acids, such as branched-chain amino acids (BCAA), lead to higher glucose-independent insulin secretion after a meal [19]. Lower concentrations of certain BCAA in blood plasma have also been demonstrated in trials, both after an eight week intervention and after a single meal with whole grain rye compared with refined wheat [20,21]. Processing can alter the microstructure, composition, and availability of different compounds and could be used to modulate the postprandial responses to a food. For example, fermentation has been shown to influence both the content and composition of dietary fiber (DF) [22] and the levels of some bioactive compounds [23] in rye products and flour.

In most studies to date on whole grain rye products such as porridge and soft bread, refined wheat bread has been used as the control product. Whole grain rye porridge and soft bread typically contain more water than soft, refined wheat bread, which gives lower energy density and may influence postprandial responses [24,25]. However, in a recent study we found that whole grain rye crisp bread, a product with low water content, promoted higher satiety, lower desire to eat, and lower hunger as well as lower energy intake in a subsequent meal compared with a soft, refined wheat bread [26]. A control product that is more similar in macrostructure and energy density may further reduce the influence of confounding factors.

The aim of the present study was to evaluate whether whole grain rye crisp bread, compared with refined wheat crisp bread, exerted beneficial effects on appetite and postprandial insulin response, as reported for other rye products. A further aim was to evaluate the effect of yeast fermentation by including one yeast fermented and one unfermented rye crisp bread as part of a breakfast.

Materials and Methods

Ethical statement

The study was carried out in agreement with the Helsinki Declaration and was approved by the regional ethics board in Uppsala on August 14, 2013 (dnr 2013/201). Recruitment started immediately after approval by the ethics board and the last participant was enrolled on August 27. The experimental work was completed by September 20, 2013. Individuals interested in participating were given written and oral information about the study and made aware of their option to withdraw from the study at any time they desired. Prior to inclusion in the study, written consent was obtained from all participants.

The study was registered at ClinicalTrials.gov (NCT02011217) after completion. The delay was due to unawareness by investigators regarding time frame for trial registration. The authors confirm that all ongoing and related trials for this drug/intervention are registered. The protocol for this trial and completed CONSORT checklist are available as supporting information, see S1 Protocol and S1 CONSORT Checklist.

Participants

Participants for the study were recruited through an advertisement in a local newspaper, through a website for clinical trials advertisements, on the Ultuna campus of the Swedish University of Agricultural Sciences (SLU), and through an internal e-mail to employees at SLU. After initial screening, men and women who met the eligibility criteria were invited to take part in the study. These criteria to were: age 18–70 years, BMI 18.5–30 kg/m2, physical activity level <2, fasting plasma glucose <6.0 mmol/L, fasting serum insulin <11 mE/L, serum TSH <2.5 mIE/L, plasma LDL <5.3 mmol/L, fasting plasma triglycerides (p-TG) <1.8 mmol/L, non-smokers, no medications likely to affect appetite, no medical conditions involving the gastrointestinal tract, no gluten intolerance or food allergies, no physical problems with eating, habitual consumption of breakfast, lunch and dinner, no dieting or self-reported fluctuations in body weight of more than 10% three months prior to screening, no recent participation in a dietary study, and no pregnancy, lactation or intention to become pregnant during the study period.

Study design

The study was conducted as a randomized, crossover trial with three different isocaloric breakfast treatments consisting of crisp breads served as part of a complete breakfast (Table 1). Test meal sequences followed a Latin square design and participants were randomly assigned, using the Excel function “Random”, to start one of the three treatments. Three commercially available crisp breads were used in the study: unfermented whole grain rye crisp bread (uRCB), yeast-fermented whole grain rye crisp bread (RCB) and yeast-fermented refined wheat crisp bread (WCB), (Barilla Sweden AB, Sweden). Flour of the same origin and composition but milled to different particle sizes was used for the production of uRCB and RCB. According to data provided by the manufacturer 30–42% of particles in the flour used for uRCB were below 125 μm and 20–28% above 1040 μm, while the same fractions in the flour used for RCB comprised 51–57% and 3–6% respectively. With the exception of particle size and the yeast added to RCB, the composition of uRCB and RCB was the same. The crisp breads were served with margarine and cheese, a glass of orange juice and a cup of coffee or tea (Table 1). Participants (Table 2) could choose between coffee and tea but had to adhere to their initial choice on all occasions. They were asked to refrain from eating, drinking and strenuous physical activity 12 hours prior to the test occasion, and to exclude alcohol and foods rich in dietary fiber from their diet per dietary guidance 24 hours before each test occasion. On the test day, participants arrived at the clinic at Uppsala University Hospital at least 10 minutes before the first appetite registration, taken at 9 am, which was 30 minutes before breakfast. Participants were instructed to finish the breakfast within 15 minutes. The test ended four hours after breakfast and participants stayed at the clinic the whole time. During this time the participants were not allowed to eat or drink anything not included in the study diet and were instructed to maintain a low physical activity. Conversation was permitted, except to discuss food or the study or to compare satiety ratings. Between each test occasion, there was a wash-out period of at least six days.

thumbnail
Download:
Table 1. Food and nutrient composition of the breakfasts used in the study1.

https://doi.org/10.1371/journal.pone.0122241.t001

thumbnail
Download:
Table 2. Age, weight and BMI of participants who completed the study.

Given as mean and standard deviation.

https://doi.org/10.1371/journal.pone.0122241.t002

Chemical analysis of foods

Crisp breads were milled with a cyclone sample mill (Retsch, Haan, Germany). Extractable and unextractable DF content and composition were analyzed according to the Uppsala method [27]. β-glucan was analyzed using a K-BGLU kit (Megazyme, Bray, Ireland) [28] and fructan content using a K-FRUC kit (Megazyme, Bray, Ireland) [29] (Table 3). Content of arabinoxylan and arabino-galactan was calculated assuming an arabinose/galactose ratio of 0.69 in extractable arabinogalactan [30]. Total fat, protein (Table 1) and amino acid composition (Table 4) were analyzed by a certified commercial testing laboratory (Eurofins, Lidköping, Sweden) using the Schmid-Bondzynski-Ratzlaff method [31], the Kjeldahl method with conversion factor 6.25 and ISO 13903:2005/13904:2005 respectively.

thumbnail
Download:
Table 3. Dietary fiber content and composition of unfermented rye crisp bread (uRCB), yeast fermented rye crisp bread (RCB) and yeast fermented refined wheat crisp bread (WCB) (% of dry matter).

https://doi.org/10.1371/journal.pone.0122241.t003

thumbnail
Download:
Table 4. Amino acid composition of the three crisp breads.

https://doi.org/10.1371/journal.pone.0122241.t004

Subjective appetite rating

Subjective appetite ratings were recorded 30 min before breakfast, at breakfast and at 30, 60, 90, 120, 150, 180, 210, and 240 min after breakfast, using an electronic visual analogue scale (VAS). On arriving at the study center, each participant was provided with a Palm computer model z22 (Palm Inc., Sunnyvale, USA) which prompted the participants to answer three questions: “How hungry do you feel right now?”, “How full do you feel right now?” and “How strong is your desire to eat right now?”. The participants marked their answer on a line anchored at each end with an extreme answer to each question; “Not at all hungry”/“Extremely hungry”, “Not at all full”/“Extremely full” and “Extremely strong”/“Not strong at all”. The computer then translated the mark to a number between 0–100. This method has been shown to give results which are in agreement with the conventional 100 mm VAS [32–34].

Physiological parameters

Venous blood was collected by trained nurses 15 minutes before breakfast and at 15, 35, 65, 95, 125, 185 and 230 minutes after breakfast. Blood samples were collected into ice cold tubes prepared with either potassium EDTA or lithium heparin (Sarstedt, Nümbrecht, Germany). Immediately after blood sampling 160 μl protease inhibitor cocktail (1 SigmaFast tablet (Sigma S8820) in 2.2 ml H2O + 5.5 μl 10 mM KR-62436(DMSO)) were added to the test tube to prevent breakdown of appetite related gut peptides and incretines, which may be analyzed later for other purposes. The samples were kept on ice and processed immediately. Blood plasma was separated from buffy coat and erythrocytes by centrifugation at 2500 g for 10 min (4°C), aliquoted into 2.0 mL screw cap micro tubes (Sarstedt, Nümbrecht, Germany) and immediately placed in a freezer at -20°C. Plasma samples were transferred and stored in a freezer maintaining a temperature of -80°C. Analyses of serum insulin and plasma glucose concentrations were performed by established routine methods at the certified laboratory of the Department of Clinical Chemistry at Uppsala University Hospital. Serum insulin was analyzed on a Roche cobas 8000 e602 module (Roche Diagnostics GmbH, Mannheim, Germany) and plasma glucose on an Architect c8000 and c16000 (Abbott, Abbott Park, Illinois, USA).

Bright field microscopy

Samples were fixed with glutaraldehyde vapor for 12 h followed by 2 h fixation with OsO4 vapor. Samples were then washed twice in distilled water, dehydrated in a series of aqueous ethanol of increasing concentration and finally infiltrated and polymerized with Technovit 7100.

The embedded samples were cut into 1.5 μm thick sections with an ultra-microtome (Leica EM UC6, Leica, Austria). The sections were stained with Lugol’s solution which stains proteins yellow, and starch dark blue/violet. It also distinguishes between amylopectin rich areas (beige/brown), and amylose (blue). The stained sections were examined using a Nikon Eclipse Ni-U microscope and the images were captured with a Nikon Digital Sight DS-Fi2 camera and processed with the software NIS-Elements BR (Nikon Instruments Inc., New York, USA).

Statistical analysis

Differences between treatments were evaluated with models appropriate for cross- over designs using PROC mixed in SAS version 9.3 (SAS Institute Inc, Cary, NC, USA). Effects of treatments were evaluated by two separate models [5]. In model 1, occasion, breakfast treatment, time (all measurement points after breakfast meal were included), time x treatment interaction and treatment x occasion interaction terms were included as fixed effects. Participant was entered as a random effect variable. In model 2, area under the curve (AUC) was used as the response variable and treatment, occasion, and the treatment x occasion interaction term were included as fixed dependent variable in the model. Participant was entered as a random factor. Total AUC was calculated for each participant and breakfast treatment, using the trapezoid rule. Differences in postprandial glucose and insulin responses were evaluated using the total area under the curve (AUCt = 0–230min) as well as for the first 120 min (AUCt = 0-120min). Response variables were log-transformed in order to approximate a normal distribution in cases where data were skewed as judged by a Shapiro-Wilks test with P<0.05. Reported values in curves are unadjusted mean unless otherwise stated. Treatment effects are reported as model-adjusted least square mean (LSM) ± standard error (SE). P-values for all main effects reported are based on models in which non-significant (P>0.10) interaction terms were removed. When a significant interaction term between treatment and time was found, t-tests were performed at each time point. P<0.05 was considered statistically significant for all tests, except for removal of interaction terms (P>0.10).

The primary outcome metric of the study was AUC for appetite ratings. With a power of 0.9 and a level of α 0.05 for a two sided test, 12 participants are sufficient to detect a 10% difference in mean appetite ratings over 4.5 hours in a comparison between two foods [35]. Secondary outcome metrics were AUC for postprandial plasma glucose and serum insulin concentration. For these, at least ten participants is needed to obtain sufficient statistical power [36].

Results

Participants

In total, 25 of the 36 participants screened were enrolled to participate in the study. Of these, three had BMI outside the range specified in the eligibility criteria but otherwise fulfilled the requirements and were deemed suitable for participation in the study. Two participants did not complete the study due to limited time. Thus a total of 23 participants completed the study and were included in the statistical evaluation. Participant’ age was 27–70 years and BMI 18–31.4 kg/m2 (Table 2). A flowchart of the study process is presented in Fig 1.

thumbnail
Download:
Fig 1. Flowchart of the study progress.

https://doi.org/10.1371/journal.pone.0122241.g001

Appetite ratings

For hunger, a significant difference between treatments was found (model 1: P = 0.004; model 2: P =. 0419). Hunger was 11% (P<0.05) lower for uRCB and 12% (P<0.05) lower for RCB compared with WCB (Fig 2). For fullness, there was a significant difference between treatments (model 1: P<0.0001; model 2: P<0.0001) (Fig 3). Fullness was 16% (P<0.001) higher for both rye crisp breads compared with WCB. For desire to eat, there was a significant difference between treatments when evaluating using model 1 (P<0.024) but not when using model 2 (AUC, P = 0.083) (Fig 4). There was no significant difference in any of the appetite ratings between uRCB and RCB.

thumbnail
Download:
Fig 2. Subjective hunger.

Left: Subjective hunger reported by n = 23 participants. Values are means. A statistically significant difference between treatments was found (P = 0.0043). Right: AUC for subjective hunger reported by n = 23 participants. A statistically significant difference between treatments was found (P = 0.0419). Values are adjusted least square means (LSM) ± standard errors (SE). Differences between treatments are given as percentage difference between the LSM values for AUC of the treatments. P<0.05 was considered significant.

https://doi.org/10.1371/journal.pone.0122241.g002

thumbnail
Download:
Fig 3. Subjective fullness.

Left: Subjective fullness reported by n = 23 participants. Values are means. A statistically significant difference between treatments was found (P<0.0001). Right: AUC for subjective fullness reported by n = 23 participants. A statistically significant difference between treatments was found (P<0.0001). Values are adjusted least square means (LSM) ± standard errors (SE). Differences between treatments are given as percentage difference between the LSM values for AUC of the treatments. P<0.05 was considered significant.

https://doi.org/10.1371/journal.pone.0122241.g003

thumbnail
Download:
Fig 4. Subjective desire to eat.

Left: Subjective desire to eat reported by n = 23 participants. Values are means. A statistically significant difference between treatments was found (P<0.0243). Right: AUC for subjective desire to eat reported by n = 23 participants. No statistically significant difference between treatments was found (P = 0.0832). Values are adjusted least square means (LSM) ± standard errors (SE).

https://doi.org/10.1371/journal.pone.0122241.g004

Postprandial glucose and insulin responses

There was no significant difference in postprandial plasma glucose concentrations between any of the treatments (Fig 5). For insulin response, a significant treatment x time interaction was observed (P<0.05). Treatments differed significantly at certain time points and significant treatment differences were found when comparing AUC values (Fig 6). The response was significantly lower for uRCB and RCB compared with WCB at 65 and 95 minutes (P<0.05). Treatments differed significantly when comparing AUCt = 0–230min (P<0.0001) and insulin secretion was 13% and 17% lower for uRCB compared with RCB (P<0.002) and WCB (P<0.001) respectively. There was no significant difference in AUCt = 0–230min between RCB and WCB, but the insulin response for uRCB was 12% and 21% lower compared to RCB (P<0.02) and WCB (P<0.001), respectively. Treatments also differed significantly when comparing AUCt = 0-120min (P<0.0001) and the insulin response was 10% lower for RCB compared with WCB (P<0.007).

thumbnail
Download:
Fig 5. Plasma glucose profile and AUC.

Left: Plasma glucose concentration- time profile in n = 23 participants. Values are means. No statistically significant effect attributed to breakfast treatment (P = 0.60) was obtained. Right: Differences in total AUC0–230 min and AUC0-120 between breakfast treatments. Values are adjusted least square means (LSM) ± standard errors (SE).

https://doi.org/10.1371/journal.pone.0122241.g005

thumbnail
Download:
Fig 6. Plasma insulin profile and AUC.

Left: Plasma insulin concentration- time profile in n = 23 participants. Values are means. A statistically significant interaction between treatment x time was detected (P<0.05). T-tests were performed for each time-point. Different letters indicate statistically significant differences between treatments at certain time points (P<0.05). Right: Differences in total AUC0–230 min and AUC0-120 between breakfast treatments. Values are adjusted least square means (LSM) ± standard errors (SE). Differences between treatments are given as percentage difference between the LSM values for AUC of the treatments. P<0.05 was considered significant.

https://doi.org/10.1371/journal.pone.0122241.g006

Microstructure

The microstructure of the rye crisp breads differed from that of the wheat crisp bread in several respects. In uRCB and RCB (Fig 7B and 7C respectively), the continuous phase was composed of highly swollen and tightly packed starch granules with the protein packed into discrete aggregates. WCB (Fig 7A) was characterized by a continuous protein network and more intact and less swollen starch granules compared with uRCB and RCB. The difference in swelling of the starch granules was most clearly seen in samples from the center and top of the products. Starch granules closer to the surface facing down during baking exhibited less swelling in all products. Furthermore, in uRCB and RCB there was leakage of amylose, visualized as blue in the micrographs, which was concentrated in the center of swollen granules in all samples and between granules in the rye crisp breads. No difference could be seen between uRCB and RCB with regard to swelling of granules and leakage of amylose. Compared with WCB, uRCB and RCB contained more aleurone layers, encapsulating mainly protein, and some intact cells, encapsulating mainly starch. There also appeared to be a higher content of intact cells and aleurone layers in uRCB compared with RCB. Moreover, RCB and WCB contained yeast cells from the fermentation incorporated in the starch or protein matrix respectively. The white areas seen in the micrographs (Fig 7) are unstained material which represented pores in the crisp bread or fibers.

thumbnail
Download:
Fig 7. Micrographs showing the microstructure at the center of the crisp bread.

(A) unfermented whole grain rye crisp bread (uRCB), (B) yeast-fermented whole grain rye crisp bread (RCB), and (C) yeast-fermented refined wheat crisp bread (WCB). Protein is colored yellow (a), amylopectin-rich areas purple (b), and amylose blue (c). Fat can be seen in WCB as brown aggregates (d) and yeast cells are present in WCB and RCB (e). Aleurone layers can be seen in uRCB and RCB (f).

https://doi.org/10.1371/journal.pone.0122241.g007

Discussion

This study evaluated effects on appetite and postprandial glucose and insulin responses after consumption of unfermented whole grain rye crisp bread, fermented whole grain rye crisp bread and fermented refined wheat crisp bread as part of a complete breakfast. The rye crisp breads induced higher fullness and less hunger as well as lower insulin response postprandially than refined wheat crisp bread. Furthermore, the postprandial insulin response appeared to be different between fermented and unfermented crisp bread.

Intake of whole grain rye products in comparison with refined wheat bread has been shown to have an appetite-reducing effect in most studies where rye products such as porridge [6–8,11] and soft breads have been investigated [7,9,10,12,13]. A recent study by Forsberg et al [26] was the first to compare fermented whole grain rye crisp bread with refined wheat soft bread. They found, under similar conditions, that the rye crisp bread promoted 20–30% higher satiety and lower hunger and desire to eat compared with refined soft wheat bread. This is a larger effect than what we have found in the current study (11–16% with regard to fullness and hunger) where the control was refined wheat crisp bread. The energy density of products is known to influence postprandial responses such as satiety and glucose concentrations to some extent [24,25]. However, in this case the refined wheat crisp bread, which had a higher energy density than the refined wheat soft bread, resulted in a smaller difference in satiety compared with whole grain rye crisp breads. Thus other factors, such as composition and microstructural features of the products and differences between the study populations, are most likely of greater importance for the differences in postprandial responses between the studies. Further, we cannot exclude that the rather wide range in age could have diluted the differences between test meals with regard to hunger and insulin response.

Certain DF have been shown to have an appetite-reducing effect [37,38] and the content and composition of fiber may have contributed to the differences observed here in appetite response between the rye and wheat crisp breads. In particular viscous forming DF has been found to be efficient in reducing acute appetite responses [38]. The rye crisp breads tested here, uRCB and RCB, had a high content of DF (20.5% and 18.3% respectively) compared with the refined wheat crisp bread control (6% DF). The viscous forming arabinoxylan constituted 2.6%, 3.0% and 0.7% (extractable) and β-glucan 2.5%, 2.1% and 0.3% in uRCB, RCB and WCB respectively (Table 3). The mechanisms behind the high satiating capacity of DF are thought to be longer exposure time during mastication [39], increased gastric distension caused by water binding and decreased gastric emptying rate due to increased viscosity [40]. Moreover, the increased viscosity may reduce the diffusion rate of enzymes and nutrients in the digesta, thereby decreasing digestion and absorption rates [41,42].

The microstructural features of crisp bread products may also affect the absorption rate of nutrients. The rye crisp breads contained intact cells and fragments of aleurone layers, which were both absent in the refined wheat bread. These cells and fragments could lead to decreased digestion rate and lower digestibility of nutrients due to encapsulation [43,44], Lower digestibility of macronutrients in high-fiber rye products compared with refined wheat products with added cellulose fiber from grain straw (Vitacel) has recently been demonstrated in ileostomized human subjects [45]. As a consequence, a larger fraction of the nutrients in the rye products is likely to reach the distal ileum and the colon where they may contribute to the ileal break [46] and fermentation [47], respectively. uRCB appeared to contain more intact cells and larger fragments of aleurone layers than RCB, which may be due to the difference in particle size distribution of the flours used for baking. However, the difference between the flours was small in comparison with that used in studies reporting an effect of particle size on postprandial responses, and most likely had limited impact on the results [7,48].

The more swollen starch granules observed in the rye crisp breads would be expected to make the starch more susceptible to enzymatic degradation [49]. However, this may be counteracted by the presence of leaked amylose, as seen in both rye crisp breads, which has been suggested to form a protective layer around the starch granules, hindering enzymatic degradation [15]. Furthermore, in addition to the soluble fibers discussed above, a higher content of undigested material in the rye crisp breads, as a consequence of decreased digestion rate and digestibility, could, contribute to an increase in the viscosity of the digesta depending on size and amount of particles, influencing gastric emptying and intestinal transit rates [50].

When combined, the composition and content of DF and the microstructural properties of the rye crisp breads may also have contributed to a prolonged effect on gastric distension and release of satiety hormones [51], resulting in increased satiety, compared to refined wheat crisp bread.

Decreased rate of release and absorption of nutrients, e.g. glucose, would be expected to result in a corresponding decrease in concentration in the blood. However, all treatments in our study elicited similar glucose response but the rye crisp breads gave slightly lower insulin concentrations, which is in line with results from earlier studies [6–16,21]. The postprandial responses could have been influenced by the additional foods included in the breakfast, which may have obscured the actual effect on postprandial glucose and insulin concentrations of the rye and wheat crisp breads. However, the contribution with regard to nutrients was approximately the same, with a small difference in fat for WCB, for all treatments. Moreover, the results are in line with those of several studies in which no additional foods were included [10,12,13].

A recent study by Eelderink et al [52] showed that differences in the in vivo digestibility and absorption of starch are not necessarily reflected in blood glucose concentration. They suggested variations in the appearance of endogenous glucose or the glucose clearance rate as possible explanations. Higher postprandial insulin concentrations after intake of WCB could lead to a faster clearance rate of glucose from the blood circulation. Glucose could therefore have been absorbed faster from the small intestine after WCB compared with RCB and particularly uRCB, without being detected as a corresponding increase in blood concentration.

The higher content of viscous DF in the rye crisp breads could be expected to result in lower postprandial glucose responses compared with WCB. Decreased postprandial blood glucose concentrations have been shown for foods supplemented with different DF, and have been attributed to increased digesta viscosity [53–56]. In a recent study glucose concentration in the portal vein of pigs was measured after intake of refined wheat bread compared with rye bread and wheat bread supplemented with isolated arabinoxylan [57]. A trend for lower glucose absorption was seen at certain time points for both the rye bread and the arabinoxylan supplemented wheat bread. Both breads also elicited lower insulin responses than the refined wheat bread. However, another study on catheterized pigs only found an effect on insulin, and not on glucose absorption, when comparing whole grain wheat bread with bread with aleurone rye flour [58]. In that case the DF content was similar for both breads, which might have influence the results. The effect of breads supplemented with arabinoxylan has also been shown in humans, on glucose peak in one case [59] and on both glucose and insulin in another [60].

Fermentation of RCB most likely induced changes in the composition and content of DF compared with uRCB, which may also have influenced digesta viscosity and glucose absorption. Fermentation has been shown to reduce the content of fructans in RCB [61,62], and to cause degradation of the viscous arabinoxylan and β-glucan due to endogenous enzymes, mainly endoxylanases [63]. Rakha et al compared several fermented and unfermented whole grain rye crisp breads and found a shift towards lower molecular weight distributions in arabinoxylans and β-glucans after fermentation [22]. This may have an impact on the viscosity and consequently absorption rate of glucose and subsequent insulin response [64].

The differences in postprandial insulin response could also be due to different amounts of insulinogenic amino acids such as the BCAA valine, isoleucine and leucine as well as the amino acids lysine and threonine. These have been suggested to mediate increased secretion of insulin and to be correlated with higher concentrations of the incretins gastric inhibitory peptide (GIP) and glucagon-like peptide-1 (GLP-1) [19,65]. Higher concentrations of GIP and GLP-1 have also been seen postprandially, after ingestion of wheat bread in comparison with rye bread [15,16]. Furthermore, in studies comparing high fiber rye bread with refined wheat bread, lower plasma concentrations of isoleucine and leucine have been shown both in a single meal setting and after an eight-week intervention [20,21]. In the present study, the product content of isoleucine was 23% and 16% lower, and the content of leucine was 22% and 18% lower in uRCB and RCB, respectively, compared with WCB. The content of threonine and valine was approximately equal in all three crisp breads while lysine content was 34% and 16% higher in uRCB and RCB, respectively, compared to WCB. The difference in contents of BCAA in the crisp breads, may have contributed to the higher postprandial insulin response for WCB compared to uRCB and RCB. Moreover, the microstructural features discussed above are also likely to be important as the intact cell structures in the rye crisp breads would decrease the availability of BCAA in comparison with WCB. This may also differ slightly between the rye crisp breads due to the finer particle size of the flour in RCB, meaning more disrupted cells. Analysis of postprandial amino acid concentrations and incretine hormones may contribute to our understanding of the involvement of BCAA in regulation of the insulin response to wheat and rye products and is therefore warranted. Additionally, it may be of interest to investigate the role of bioactive compounds, such as benzoxazinoids and phenolic acids, in regulation of appetite and postprandial insulin and glucose responses [10,66,67]. The availability and absorption kinetics of these can be influenced by processing, e.g., yeast fermentation [68,69]. The extent to which bioactive compounds will contribute to the appetite regulation is still unknown.

Conclusions

Unfermented (uRCB) and fermented (RCB) whole grain rye crisp bread as part of a complete breakfast induced higher satiety up to 4h after intake compared with refined wheat crisp bread (WCB). This difference was most likely due to higher content of dietary fiber, mainly viscous arabinoxylans and β-glucans, and microstructural features of the rye crisp breads.

Lower postprandial insulin concentrations, but no difference in glucose concentrations, were observed for both rye crisp breads compared with WCB and for uRCB compared with RCB. These differences in insulin responses may be due to altered glucose absorption kinetics caused by content- and process-induced changes in composition of dietary fiber in RCB and WCB, and higher content and availability of insulinogenic branched chain amino acids in WCB. Additionally, we cannot rule out effects of slight differences in particle size distribution.

Supporting Information

S1 CONSORT Checklist. Completed CONSORT checklist.

https://doi.org/10.1371/journal.pone.0122241.s001

(DOC)

S1 Dataset. Raw data for glucose, insulin and subjective appetite ratings.

https://doi.org/10.1371/journal.pone.0122241.s002

(XLSX)

S1 Protocol. Trial protocol.

https://doi.org/10.1371/journal.pone.0122241.s003

(DOCX)

Acknowledgments

We would like to thank the volunteers participating for in the study. We also want to thank Gunnel Fransson for conducting the fiber analysis. Barilla Sweden AB is acknowledged for providing the crisp breads used in the study.

Author Contributions

Conceived and designed the experiments: RL. Performed the experiments: IL RL DPJ. Analyzed the data: RL ML IL DPJ UR. Wrote the paper: DPJ. Reviewed the study protocol: UR.

References

  1. 1. Swinburn BA, Sacks G, Hall KD, McPherson K, Finegood DT, Moodie ML, et al. (2011) The global obesity pandemic: shaped by global drivers and local environments. Lancet 2011;378: 804–814. pmid:21872749
  2. 2. Mozaffarian D, Hao T, Rimm EB, Willett WC, Hu FB. Changes in Diet and Lifestyle and Long-Term Weight Gain in Women and Men. N Engl J Med 2011;364: 2392–2404. pmid:21696306
  3. 3. Wirfält E, Drake I, Wallström P. What do review papers conclude about food and dietary patterns? Food Nutr Res 2013;57. Available: http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=3589439&tool=pmcentrez&rendertype=abstract.
  4. 4. Hetherington MM, Cunningham K, Dye L, Gibson EL, Gregersen NT, Halford JCG, et al. Potential benefits of satiety to the consumer: scientific considerations. Nutr Res Rev 2013;26: 22–38. pmid:23680169
  5. 5. Blundell J, de Graaf C, Hulshof T, Jebb S, Livingstone B, Lluch A, et al. Appetite control: methodological aspects of the evaluation of foods. Obes Rev 2010;11: 251–270. pmid:20122136
  6. 6. Isaksson H, Tillander I, Andersson R, Olsson J, Fredriksson H, Webb D-L, et al. Whole grain rye breakfast—sustained satiety during three weeks of regular consumption. Physiol Behav 2012;105: 877–884. pmid:22061429
  7. 7. Isaksson H, Rakha A, Andersson R, Fredriksson H, Olsson J, Åman P. Rye kernel breakfast increases satiety in the afternoon—an effect of food structure. Nutr J 2011;10: 31. pmid:21481225
  8. 8. Isaksson H, Sundberg B, Åman P, Fredriksson H, Olsson J. Whole grain rye porridge breakfast improves satiety compared to refined wheat bread breakfast. Food Nutr Res 2008;52: 1–7.
  9. 9. Isaksson H, Fredriksson H, Andersson R, Olsson J, Åman P. Effect of rye bread breakfasts on subjective hunger and satiety: a randomized controlled trial. Nutr J 2009;8: 39. pmid:19709412
  10. 10. Rosén LAH, Östman EM, Björck IME. Postprandial glycemia, insulinemia, and satiety responses in healthy subjects after whole grain rye bread made from different rye varieties. 1. J Agric Food Chem 2011;59: 12149–12154. pmid:21981244
  11. 11. Rosén LAH, Silva LOB, Andersson UK, Holm C, Östman EM, Björck IME. Endosperm and whole grain rye breads are characterized by low post-prandial insulin response and a beneficial blood glucose profile. Nutr J 2009;8: 42. pmid:19781071
  12. 12. Rosén LAH, Östman EM, Björck IME. Postprandial glycemia, insulinemia, and satiety responses in healthy subjects after whole grain rye bread made from different rye varieties. 2. J Agric Food Chem 2011;59: 12149–12154. pmid:21981244
  13. 13. Rosén LAH, Ostman EM, Björck IM. Effects of cereal breakfasts on postprandial glucose, appetite regulation and voluntary energy intake at a subsequent standardized lunch; focusing on rye products. Nutr J 2011;10: 7. pmid:21247415
  14. 14. Leinonen K, Liukkonen K, Poutanen K, Uusitupa M, Mykkänen H. Rye bread decreases postprandial insulin response but does not alter glucose response in healthy Finnish subjects. Eur J Clin Nutr 1999;53: 262–267. pmid:10334650
  15. 15. Juntunen KS, Laaksonen DE, Autio K, Niskanen LK, Holst JJ, Savolainen KE, et al. Structural differences between rye and wheat breads but not total fiber content may explain the lower postprandial insulin response to rye bread. Am J Clin Nutr 2003;78: 957–964. pmid:14594782
  16. 16. Juntunen KS, Niskanen LK, Liukkonen KH, Poutanen KS, Holst JJ, Mykkänen HM. Postprandial glucose, insulin, and incretin responses to grain products in healthy subjects. Am J Clin Nutr 2002;75: 254–262. pmid:11815315
  17. 17. Hu FB, Dam RM Van, Liu S. Diet and risk of Type II diabetes: the role of types of fat and carbohydrate. Diabetolgia 2001;44: 805–817.
  18. 18. Del Prato S, Leonetti F, Simonson DC, Sheehan P, Matsuda M, DeFronzo RA. Effect of sustained physiologic hyperinsulinaemia and hyperglycaemia on insulin secretion and insulin sensitivity in man. Diabetologia 1994;37: 1025–1035. pmid:7851681
  19. 19. Gunnerud UJ, Heinzle C, Holst JJ, Östman EM, Björck IME. Effects of pre-meal drinks with protein and amino acids on glycemic and metabolic responses at a subsequent composite meal. PLoS One 2012;7: e44731. Available: http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=3446992&tool=pmcentrez& pmid:23028596
  20. 20. Moazzami AA, Bondia-Pons I, Hanhineva K, Juntunen K, Antl N, Poutanen K. Metabolomics reveals the metabolic shifts following an intervention with rye bread in postmenopausal women—a randomized control trial. Nutr J 2012;11: 88. pmid:23088297
  21. 21. Moazzami AA, Shrestha A, Morrison DA, Poutanen K, Mykka H. Metabolomics Reveals Differences in Postprandial Responses to Breads and Fasting Metabolic Characteristics Associated with Postprandial Insulin Demand in Postmenopausal Women 1–3. J Nutr. 2014:
  22. 22. Rakha A, Åman P, Andersson R. Characterisation of dietary fibre components in rye products. Food Chem 2010;119: 859–867.
  23. 23. Katina K, Liukkonen K-H, Kaukovirta-Norja A, Adlercreutz H, Heinonen S-M, Lampi A-M, et al. Fermentation-induced changes in the nutritional value of native or germinated rye. J Cereal Sci 2007;46: 348–355.
  24. 24. Burton P, Lightowler HJ. Influence of bread volume on glycaemic response and satiety. Br J Nutr 2007;96: 877–882.
  25. 25. Rolls BJ, Castellanos VH, Halford JC, Kilara A, Panyam D, Pelkman CL, et al. Volume of food consumed affects satiety in men. Am J Clin Nutr 1998;67: 1170–1177. pmid:9625090
  26. 26. Forsberg T, Åman P, Landberg R. Effects of whole grain rye crisp bread for breakfast on appetite and energy intake in a subsequent meal: two randomised controlled trails with different amounts of test foods and breakfast energy content. Nutr J 2014;13: 26. pmid:24661836
  27. 27. Theander O, Åman P, Westerlund E, Andersson R, Pettersson D. Total dietary fiber determined as neutral sugar residues, uronic acid residues and Klason lignin (the Uppsala method): collaborative study. J AOAC Int 1995;78: 1030–1044. pmid:7580315
  28. 28. Mccleary BV, Codd R. Measurment of (1–3), (1–4)-beta-d-Glucan in Barley and Oats: A Streamlined Enzymic Procedure. J Sci Food Agric 1991;55: 303–312.
  29. 29. McCleary BV, Murphy A, Mugford DC. Measurement of total fructan in foods by enzymatic/spectrophotometric method: collaborative study. J AOAC Int 2000;83: 356–364. pmid:10772173
  30. 30. Loosveld AA, Grobet PJ, Delcour JA. Contents and Structural Features of Water-Extractable Arabinogalactan in Wheat Flour Fractions. J Agric Food Chem 1997;45: 1998–2002.
  31. 31. Croon L-B, Fuchs G. Fetthaltsbestämning i mjöl och mjölprodukter. Vår föda 1980;32: 425–476.
  32. 32. Stubbs RJ, Hughes DA, Johnstone AM, Rowley E, Reid C, Elia M, et al. Review article The use of visual analogue scales to assess motivation to eat in human subjects: a review of their reliability and validity with an evaluation of new hand-held computerized systems for temporal tracking of appetite ratings. Br J Nutr 2000;84: 405–415. pmid:11103211
  33. 33. Stubbs RJ, Hughes DA, Johnstone AM, Rowley E, Ferris S, Elia M, et al. Description and evaluation of a Newton-based electronic appetite rating system for temporal tracking of appetite in human subjects. Physiol Behav 2001;72: 615–619. pmid:11282147
  34. 34. Stratton RJ, Stubbs RJ, Hughes D, King N, Blundell JE, Elia M. Comparison of the traditional paper visual analogue scale questionnaire with an Apple Newton electronic appetite rating system (EARS) in free living subjects feeding ad libitum. Eur J Clin Nutr 1998;52: 737–741 pmid:9805221
  35. 35. Flint A, Raben A, Blundell JE, Astrup A. Reproducibility, power and validity of visual analogue scales in assessment of appetite sensations in single test meal studies. Int J Obes Relat Metab Disord 2000;24: 38–48. pmid:10702749
  36. 36. Brouns F, Bjorck I, Frayn KN, Gibbs AL, Lang V, Slama G, et al. Glycaemic index methodology. Nutr Res Rev 2005;18: 145–171. pmid:19079901
  37. 37. Clark MJ, Slavin JL. The effect of fiber on satiety and food intake: a systematic review. J Am Coll Nutr 2013;32: 200–211. pmid:23885994
  38. 38. Wanders AJ, van den Borne JJGC, de Graaf C, Hulshof T, Jonathan MC, Kristensen M, et al. Effects of dietary fibre on subjective appetite, energy intake and body weight: a systematic review of randomized controlled trials. Obes Rev 2011;12: 724–739. pmid:21676152
  39. 39. Wanders AJ, Jonathan MC, van den Borne JJGC, Mars M, Schols H A, Feskens EJM, et al. The effects of bulking, viscous and gel-forming dietary fibres on satiation. Br J Nutr 2013;109: 1330–1337. pmid:22850326
  40. 40. Marciani L, Gowland PA, Spiller RC, Manoj P, Moore RJ, Young P, et al. Effect of meal viscosity and nutrients on satiety, intragastric dilution, and emptying assessed by MRI. Am J Physiol Gastrointest Liver Physiol 2001;280: G1227–33. pmid:11352816
  41. 41. Shelat KJ, Vilaplana F, Nicholson TM, Wong KH, Gidley MJ, Gilbert RG. Diffusion and viscosity in arabinoxylan solutions: Implications for nutrition. Carbohydr Polym 2010;82: 46–53.
  42. 42. Shelat KJ, Vilaplana F, Nicholson TM, Gidley MJ, Gilbert RG. Diffusion and rheology characteristics of barley mixed linkage β-glucan and possible implications for digestion. Carbohydr Polym 2011;86: 1732–1738.
  43. 43. Le Gall M, Serena A, Jørgensen H, Theil PK, Bach Knudsen KE. The role of whole-wheat grain and wheat and rye ingredients on the digestion and fermentation processes in the gut—a model experiment with pigs. Br J Nutr 2009;102: 1590–1600. pmid:19635175
  44. 44. Bach Knudsen KE, Serena A, Kjaer AKB, Jørgensen H, Engberg R. Rye bread enhances the production and plasma concentration of butyrate but not the plasma concentrations of glucose and insulin in pigs. J Nutr 2005;135: 1696–1704. pmid:15987852
  45. 45. Isaksson H, Landberg R, Sundberg B, Lundin E, Hallmans G, Zhang J-X, et al. High-fiber rye diet increases ileal excretion of energy and macronutrients compared with low-fiber wheat diet independent of meal frequency in ileostomy subjects. Food Nutr Res 2013;57. Available: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3862981/.
  46. 46. Maljaars PWJ, Peters HPF, Mela DJ, Masclee AAM. Ileal brake: a sensible food target for appetite control. A review. Physiol Behav 2008;95: 271–281. pmid:18692080
  47. 47. Cani PD, Lecourt E, Dewulf EM, Sohet FM, Pachikian BD, Naslain D, et al. Gut microbiota fermentation of prebiotics increases satietogenic and incretin gut peptide production with consequences for appetite sensation and glucose response after a meal. Am J Clin Nutr 2009;90: 1236–1243. pmid:19776140
  48. 48. Heaton KW, Marcus SN, Emmett PM, Bolton CH. Particle size of wheat, maize, and oat test meals: effects on plasma glucose and insulin responses and on the rate of starch digestion in vitro. Am J Clin Nutr 1988;47: 675–682. pmid:2451416
  49. 49. Holm J, Lundquist J, Björck IME, Eliasson A-C, Asp N-G. Degree in vitro, of starch gelatinization, and metabolic response in rats. Am J Clin Nutr 1988;47: 1010–1016. pmid:3287891
  50. 50. Lentle RG, Janssen PWM. Physical characteristics of digesta and their influence on flow and mixing in the mammalian intestine: a review. J Comp Physiol B 2008;178: 673–690. pmid:18401586
  51. 51. De Graaf C, Blom WAM, Smeets PAM, Stafleu A, Hendriks HFJ. Biomarkers of satiation and satiety. Am J Clin Nutr 2004;79: 946–961. pmid:15159223
  52. 52. Eelderink C, Moerdijk-poortvliet TCW, Wang H, Schepers M, Preston T, Boer T, et al. The Glycemic Response Does Not Reflect the In Vivo Starch Digestibility of Fiber-Rich Wheat Products in Healthy Men. J Nutr 2012;142: 258–263. pmid:22223569
  53. 53. Ellis PR, Roberts FG, Low AG, Morgan LM. The effect of high-molecular-weight guar gum on net apparent glucose absorption and net apparent insulin and gastric inhibitory polypeptide production in the growing pig: relationship to rheological changes in jejunal digesta. Br J Nutr 1995;74: 539–556. pmid:7577892
  54. 54. Fabek H, Messerschmidt S, Brulport V, Goff HD. The effect of in vitro digestive processes on the viscosity of dietary fibres and their influence on glucose diffusion. Food Hydrocoll 2014;35: 718–726.
  55. 55. Lightowler HJ, Henry CJK. Glycemic response of mashed potato containing high-viscocity hydroxypropylmethylcellulose. Nutr Res 2009;29: 551–557. pmid:19761889
  56. 56. Östman E, Rossi E, Larsson H, Brighenti F, Björck I. Glucose and insulin responses in healthy men to barley bread with different levels of (1→3;1→4)-β-glucans; predictions using fluidity measurements of in vitro enzyme digests. J Cereal Sci 2006;43: 230–235.
  57. 57. Christensen KL, Hedemann MS, Lærke HN, Jørgensen H, Mutt SJ, Herzig K-H, et al. Concentrated Arabinoxylan but Not Concentrated β-Glucan in Wheat Bread Has Similar E ff ects on Postprandial Insulin as Whole-Grain Rye in Porto-arterial Catheterized Pigs. J Agric Food Chem 2013;61: 7760–7768. pmid:23919413
  58. 58. Theil PK, Jørgensen H, Serena A, Hendrickson J, Bach Knudsen KE. Products deriving from microbial fermentation are linked to insulinaemic response in pigs fed breads prepared from whole-wheat grain and wheat and rye ingredients. Br J Nutr 2011;105: 373–383. pmid:20923581
  59. 59. Hartvigsen ML, Gregersen S, Lærke HN, Holst JJ, Bach Knudsen KE, Hermansen K. Effects of concentrated arabinoxylan and β-glucan compared with refined wheat and whole grain rye on glucose and appetite in subjects with the metabolic syndrome: a randomized study. Eur J Clin Nutr 2014;68: 84–90. pmid:24253758
  60. 60. Lu ZX, Walker KZ, Muir JG, O’Dea K. Arabinoxylan fibre improves metabolic control in people with Type II diabetes. Eur J Clin Nutr 2004;58: 621–628. pmid:15042130
  61. 61. Nilsson U, Öste R, Jägerstad M. Cereal fructans: Hydrolysis by yeast invertase, in vitro and during fermentation. J Cereal Sci 1987;6: 53–60.
  62. 62. Andersson R, Fransson G, Tietjen M, Åman P. Content and molecular-weight distribution of dietary fiber components in whole-grain rye flour and bread. J Agric Food Chem 2009;57: 2004–2008. pmid:19219994
  63. 63. Rakha A, Åman P, Andersson R. How does the preparation of rye porridge affect molecular weight distribution of extractable dietary fibers? Int J Mol Sci 2011;12: 3381–3393. pmid:21686191
  64. 64. Izydorczyk MS, Biliaderis CG. Cereal arabinoxylans: advances in structure and physicochemical properties. Carbohydr Polym 1995;28: 33–48.
  65. 65. Nilsson M, Stenberg M, Frid AH, Holst JJ, Björck IME. Glycemia and insulinemia in healthy subjects after lactose-equivalent meals of milk and other food proteins: the role of plasma amino acids and incretins. Am J Clin Nutr 2004;80: 1246–1253. pmid:15531672
  66. 66. Rosenfeld MJ, Forsberg SR. Compounds for use in weight loss and appetite supression in humans. Patent (US 7507731 B2) 2009.
  67. 67. Slavin J. Why whole grains are protective: biological mechanisms. Proc Nutr Soc 2003;62: 129–134. pmid:12740067
  68. 68. Bondia-Pons I, Aura A-M, Vuorela S, Kolehmainen M, Mykkänen H, et al. Rye phenolics in nutrition and health. J Cereal Sci 2009;49: 323–336.
  69. 69. Nordlund E, Katina K, Aura A-M, Poutanen K. Changes in bran structure by bioprocessing with enzymes and yeast modifies the in vitro digestibility and fermentability of bran protein and dietary fibre complex. J Cereal Sci 2013;58: 200–208.