DF: Diabetes (2008)


Tapola N, Karvonen H, Niskanen L, Mikola M, Sarkkinen E.Glycemic responses of oat bran products in type 2 diabetic patients. Nutr Metab Cardiovasc Dis. 2005 Aug; 15 (4): 255-261. PMID: 16054549.

PubMed ID: 16054549
Study Design:
Randomized Crossover Trial
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Quality Rating:
Neutral NEUTRAL: See Quality Criteria Checklist below.
Research Purpose:
  1. To assess the post-prandial glycemic response of two different oat bran products (oat bran flour and oat bran crisp)
  2. Test the hypothesis that oat flour can decrease the glucose response following an oral glucose load.
Inclusion Criteria:
  • Previously-diagnosed type 2 diabetes mellitus, treated with diet-only or a fasting plasma glucose value above 7.0mmol per L
  • Age 18 to 75 years
  • Body mass index under 35kg per m2.
Exclusion Criteria:
  • Administration of any anti-hyperglycemic therapy
  • Presence of hepatic, renal or thyroid dysfunction
  • History of unstable coronary artery disease [i.e., myocardial infarction, unstable angina pectoris, coronary artery bypass graft (CABG) or percutaneous transluminal coronary angioplasty (PTCA) within the previous six months]
  • Temporal ischemic attack or stroke within six months prior to screening
  • History of cancer
  • Presence of celiac disease or other clinically significant gastrointestinal disease
  • Presence or history of allergic reaction to oat.
Description of Study Protocol:


Not described.


Randomized controlled, repeated-measures design with two test series.

All subjects participated in five two-hour meal glucose tolerance tests in the same order. The order of the test series was randomly determined, except for the oat bran flour meal, which was given first to ensure that the subject could drink enough water so that subsequently the amount of water would be the same for both the oat bran flour and crisp meals. The order of the meals was as follows:

  • Oat bran flour
  • Oat bran crisps
  • 12.5g glucose load (Series One)
  • 25g glucose load
  • 25g glucose load in the presence of 30g oat bran flour (Series Two).

The subjects were told to maintain their diet, body weight and living habits throughout the study. The subjects were requested to refrain from intensive physical activity the day before and abstain from alcohol two days before the meal glucose tolerance test. In addition, the subjects were instructed to consume identical evening meals on the evening before each meal glucose tolerance test.

Body weight was measured with a digital scale (Scale Seca 707, Vogel & Falke GmpH & Co., Germany). Weight measurement was repeated twice and the mean value was used in the analyses. In addition, body weight was measured before the last glucose tolerance test. Previous and current diseases and current medication were ascertained at the screening visit by interview, using a structured questionnaire.

Blinding Used

Not described.


The experiment began in the morning after a 12-hour overnight fast. After the fasting blood sample was taken, the subjects consumed the test meal within 15 minutes. Finger-prick capillary blood analysis was carried out at 15, 30, 45, 60, 90 and 120 minutes after starting to eat.

Description of the Two Series

Series One: 12.5g Glycemic (Available) Carbohydrate

  • Cold water was mixed into oat bran flour (61.6g) and cold water (250g) was poured onto oat bran crisp (29.1g). The same amount of artificial sweetener (zero to one gram) was used both with the oat bran flour and crisp meal.
  • Glucose dissolved in 250g of water was the reference. In addition, the oat bran flour meal was served with 250g water, of which the subjects drank as much as they liked. The same amount of water was consumed also with the oat bran crisp meal.
    • Oat bran flour (NATUREAL® GI-flour, Finn Cereal, Vantaa, Finland)
    • Oat bran crisps (NATUREAL® GI-crisp, Finn Cereal, Vantaa, Finland). These oat bran products are made using milling and cooking extrusion to add the solubility and viscosity of β-glucan and at the same time keep the high molecular weight unaffected. Oat bran crisps consisted of oat bran (70%) and starch (30%).
    • Glucose (12.5g; glucosum anhydricum, Oriola Oy, Espoo, Finland).

Series Two

  • Oat bran flour (30g, providing 6.1g glycemic carbohydrate) and glucose solution were mixed in a shaker just before eating
  • The glucose solution was made dissolving 25g of glucose in 250g of water. Glucose solution without oat bran flour was used as a reference.
  • Participants consumed 150g of coffee (with artificial sweetener if desired) with all intervention meals.

Statistical Analysis

  • Areas under the plasma glucose response curve (AUC) were calculated using Canvas 8.0.2 (Deneba Software, Miami, USA) for each subject, ignoring the area below the fasting (zero minutes) concentration
  • Shapiro-Wilk test (normal distribution of variables checked)
  • GLM repeated measures followed by the paired samples T-test, adjusted with the Bonferroni correction for pairwise comparisons
  •  P<0.05.
Data Collection Summary:

Timing of Measurements

  • Blood samples for routine laboratory measurements
    • Screening visit (one to two weeks before the first meal glucose tolerance test).
  • Height and body weight
    • Screening visit (one to two weeks before the first meal glucose tolerance test).
  • Glucose (fingerstick)
    • Zero, 15, 30, 45, 60, 90 and 120 minutes post-prandial.

Dependent Variables

Blood glucose concentrations. 

Independent Variables

  • Oat bran flour
  • Oat bran crisps
  • Glucose.

Control Variables

Body weight.

Description of Actual Data Sample:
  • Initial N: 13 (not described) 
  • Attrition (final N): 12 subjects (seven male, five female)
  • Age: 66±7 years
  • Ethnicity: Not described.

Other Relevant Demographics

  • Body mass index: 28.9±3.5
  • Pretrial fasting plasma glucose concentration: 7.1±0.7mmol per L.


Kuopio, Finland.

Summary of Results:

Post-Prandial Glucose Responses After Consuming the Oat Bran Flour, the Oat Bran Crisp and the Glucose Load (N=12; Mean (SD)]

Oat Bran Flour
Oat Bran Crisp
12.5g Glucose Load

Oat Bran Flour P-Value

Oat Bran Crisp P-Value
Incremental Change From the Baseline (Δmmol/L)   0.002 NS
15 minutes 0.2 (0.4) 0.5 (0.7) 1.4 (0.7) <0.006  
30 minutes 0.3 (0.4) 1.1 (0.6) 2.7 (0.7) <0.006  
45 minutes 0.4 (0.6) 1.2 (0.5) 2.2 (0.6) <0.006  
60 minutes 0.5 (0.8) 1.1 (0.5) 1.1 (0.7) NS  
90 minutes 0.3 (0.7) 0.8 (0.7) −0.3 (0.5) NS  
120 minutes 0.1 (0.6) 0.2 (0.6) −0.6 (0.4) 0.012  
Area under curve (mmol min/L)     
0 to 60 minutes 21 (19) 52 (25) 102 (27) <0.002 <0.002
0 to 120 minutes 47 (45) 93 (41) 118 (40) <0.002 NS

Post-Prandial Glucose Responses After Consuming 25g Glucose Load Alone and in the Presence of 30g Oat Bran Flour [N=12; Mean (SD)]

  25g Glucose Load+30g Oat Bran Flour 25g Glucose Load P-Value
Incremental change from the baseline (Δmmol/l)   0.002
15 minutes 1.0 (0.9) 2.0 (0.6) NS
30 minutes 2.6 (1.0) 4.1 (0.8) 0.006
45 minutes 2.9 (0.8) 4.4 (0.9) <0.006
60 minutes 2.7 (1.4) 3.6 (1.4) 0.012
90 minutes 1.9 (1.2) 1.8 (1.2) NS
120 minutes 1.3 (1.4) 0.1 (0.9) <0.006
Area under curve (mmol min/L)   
0 to 60 minutes 118 (41) 185 (34) <0.001
0 to 120 minutes 237 (96) 298 (81) 0.003

Other Findings

  • Glucose was lower at 15, 30 and 45 minutes with oat bran flour and oat bran crisp
  • Rise in glucose was lower at 15, 30, 45 and 120 minutes with oat bran flour
  • AUC one to 60 minutes was smaller with oat bran flour and oat bran crisp
  • The addition of oat bran flour to glucose decreased the zero-to-60-minute and zero-to-120-minute AUC by 35±21% and 22±20%, respectively.
Author Conclusion:
  • This study showed that the addition of oat bran flour high in B-glucan to a meal produced a decrease in post-prandial glycemic response in subjects with type 2 diabetes
  • The oat bran flour may be useful in making food applications with increased soluble fiber levels and low GI.
Funding Source:
Oy Foodfiles, Finn Cereal (both Finland)
Food Company:
University/Hospital: University of Kuopio
Reviewer Comments:
  • Small sample size
  • No description of recruitment or randomization methods
  • No knowledge of duration of diabetes
  • No mention of study sponsor or discussion of limitations.
Quality Criteria Checklist: Primary Research
Relevance Questions
  1. Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies) Yes
  2. Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about? Yes
  3. Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice? Yes
  4. Is the intervention or procedure feasible? (NA for some epidemiological studies) Yes
Validity Questions
1. Was the research question clearly stated? Yes
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? Yes
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? Yes
  1.3. Were the target population and setting specified? Yes
2. Was the selection of study subjects/patients free from bias? ???
  2.1. Were inclusion/exclusion criteria specified (e.g., risk, point in disease progression, diagnostic or prognosis criteria), and with sufficient detail and without omitting criteria critical to the study? Yes
  2.2. Were criteria applied equally to all study groups? Yes
  2.3. Were health, demographics, and other characteristics of subjects described? Yes
  2.4. Were the subjects/patients a representative sample of the relevant population? ???
3. Were study groups comparable? Yes
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) ???
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? N/A
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) Yes
  3.4. If cohort study or cross-sectional study, were groups comparable on important confounding factors and/or were preexisting differences accounted for by using appropriate adjustments in statistical analysis? N/A
  3.5. If case control study, were potential confounding factors comparable for cases and controls? (If case series or trial with subjects serving as own control, this criterion is not applicable.) N/A
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? N/A
4. Was method of handling withdrawals described? Yes
  4.1. Were follow-up methods described and the same for all groups? Yes
  4.2. Was the number, characteristics of withdrawals (i.e., dropouts, lost to follow up, attrition rate) and/or response rate (cross-sectional studies) described for each group? (Follow up goal for a strong study is 80%.) Yes
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  4.4. Were reasons for withdrawals similar across groups? N/A
  4.5. If diagnostic test, was decision to perform reference test not dependent on results of test under study? N/A
5. Was blinding used to prevent introduction of bias? Yes
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? No
  5.2. Were data collectors blinded for outcomes assessment? (If outcome is measured using an objective test, such as a lab value, this criterion is assumed to be met.) Yes
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? N/A
  5.4. In case control study, was case definition explicit and case ascertainment not influenced by exposure status? N/A
  5.5. In diagnostic study, were test results blinded to patient history and other test results? N/A
6. Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described? Yes
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? Yes
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? N/A
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? Yes
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? Yes
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? N/A
  6.6. Were extra or unplanned treatments described? N/A
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? N/A
  6.8. In diagnostic study, were details of test administration and replication sufficient? N/A
7. Were outcomes clearly defined and the measurements valid and reliable? Yes
  7.1. Were primary and secondary endpoints described and relevant to the question? Yes
  7.2. Were nutrition measures appropriate to question and outcomes of concern? Yes
  7.3. Was the period of follow-up long enough for important outcome(s) to occur? Yes
  7.4. Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures? Yes
  7.5. Was the measurement of effect at an appropriate level of precision? Yes
  7.6. Were other factors accounted for (measured) that could affect outcomes? Yes
  7.7. Were the measurements conducted consistently across groups? Yes
8. Was the statistical analysis appropriate for the study design and type of outcome indicators? Yes
  8.1. Were statistical analyses adequately described and the results reported appropriately? Yes
  8.2. Were correct statistical tests used and assumptions of test not violated? Yes
  8.3. Were statistics reported with levels of significance and/or confidence intervals? Yes
  8.4. Was "intent to treat" analysis of outcomes done (and as appropriate, was there an analysis of outcomes for those maximally exposed or a dose-response analysis)? Yes
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? N/A
  8.6. Was clinical significance as well as statistical significance reported? Yes
  8.7. If negative findings, was a power calculation reported to address type 2 error? N/A
9. Are conclusions supported by results with biases and limitations taken into consideration? No
  9.1. Is there a discussion of findings? Yes
  9.2. Are biases and study limitations identified and discussed? No
10. Is bias due to study's funding or sponsorship unlikely? ???
  10.1. Were sources of funding and investigators' affiliations described? No
  10.2. Was the study free from apparent conflict of interest? Yes