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DF: Obesity (2008)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:

To determine the effect of particle size (flour vs. flakes) on glycemic responses after oats and barley (Prowashonupana cultivar), which contain high amounts of soluble fiber, are consumed by overweight women.

Inclusion Criteria:

Women, 28 to 58 years of age who were:

  • Weight stable for six months before the study
  • Over 25% body fat
  • Taking no medication known to alter glucose metabolism or lipid metabolism
  • Health history questionnaire completion
  • Screened for underlying disease by a routine urinalysis and blood screen
Exclusion Criteria:
  • Abnormal fasting glucose
  • Evidence of an infection
  • Hypertensive
Description of Study Protocol:
  • Recruitment: Not described, but eligibility assessed after medical screening
  • Design: Randomized trial with crossover design; treatment order based on a Latin square design with an 11-day washout period
  • Blinding used: Not described

Intervention

Consumed glucose (one gram per kg body weight) and four test breakfast meals consisting of 0.33g per kg body weight of carbohydrate from pudding (predominantly sucrose) and 0.67g per kg body weight of carbohydrate from oat flour, oatmeal, barley flour or barley cereal, for a total of one gram carbohydrate per kg body weight.

  • The test meals were weighed for each subject and cooked (in a microwave oven) with water the day of the tolerance test
  • Water used for cooking and for drinking during consumption of the test meals equaled the volume (three grams per kg body weight) consumed during the glucose tolerance test
  • Subjects were asked to consume the test meals within 10 minutes
  • Total carbohydrate averaged 73.7g and 76.1g per test for oats and barley, respectively
  • B-Glucan consumption averaged 3.23g for oat test meals and 12.1g for barley test meals.

Statistical Analysis

  • Mixed-models procedure for repeated-measures analysis of variance (PCSAS, version 8.2, SAS Institute, Cary, NC)
  • Data were evaluated for the main effects of particle size (glucose, flakes and flour), response (time) and period
  • Insulin values were log-transformed for homogeneity
  • Least-squares means (SEMs)
  • Critical level of significance of P<0.05.
Data Collection Summary:

Timing of Measurements

 Blood samples were collected at fasting and at 30, 60, 120 and 180 minutes after the acute loads.

  • Glucose-automated spectrophotometric system (CentrificChem System 500, Union Carbide, Trace-America, Miami, FL)
  • Insulin (ICN Biomedicals, Inc., Irvine, CA); radioimmunoassay
  • Glucagon, TSH (Diagnostics Products Corporation, Los Angeles, CA); radioimmunoassay
  • Leptin (Linco Research, St. Charles, MO); radioimmunoassay
  • Two-hour response area under the curve (AUC) was calculated by using the method of Gannon and Nutall, which uses post-prandial differences above fasting concentrations for glucose and insulin
  • Insulin resistance; homeostasis model assessment (HOMA=insulinuU/mlx glucosemmol/L/22.5), Cederholm [(IRCederholm =m/mpg/log10(msi)] and a method using a published index of glucose disposal rate, corrected for fat-free mass, based on fasting insulin and triglyceride concentrations (MFFM=EXP) 2.63-0.28x(log insulinnmol/L)-0.31x(log triacylglycerolmmol/L).

Dependent Variables

  • Glucose
  • Insulin
  • Glucagon
  • Thyroid Stimulating Hormone
  • Leptin
  • Insulin resistance.

Independent Variables

Type and form of cereal.

Control Variables

 N/A.

Description of Actual Data Sample:
  • Initial N: 10 women
  • Attrition (final N): Not described
  • Age: 50.1±7.7 (range 37 to 60)
  • Ethnicity: Not described
  • Anthropometrics: 30.3±2.2 (range 25.8 to 32.9)
  • Location: Diet and Human Performance Laboratory, Beltsville Human Nutrition Research Center, Agricultural Research Service, US Department of Agriculture, Beltsville, Maryland.
Summary of Results:

Fasting, Area Under the Curve (AUC) and Calculated Insulin Resistance Values After the Glucose and Grain Meals*

 

Meals

ANOVA

Glucose

Oat Flour

Oatmeal

Barley Flour

Barley Flakes

Fasting Glucose (mmol/L)

4.29±0.13

4.47±0.13

4.43±0.13

4.62±0.13

4.51±0.13

P=0.289

Fasting Insulin (pmol/L)

69.8±15.2

64.4±15.2

60.8±15.2

75.4±15.2

66.3±15.2

P=0.691

Fasting Glucagon (ng/L)

42.6±4.7

51.0±4.7

37.9±4.7

51.8±4.7

48.7±4.7

P=0.204

Fasting Leptin (µg/L)

14.0±1.2

14.8±1.2

13.0±1.2

12.5±1.2

11.6±1.2

P=0.099

Glucose AUC (mmol x min/L)†

171.4±16.3a

109.3±16.3bc

122.4±16.3b

70.0±16.3cd

60.6±16.3d

P<0.002

Insulin AUC (nmol x min/L)

31.6±3.1a3

29.8±3.1a

27.6±3.1a

17.6±3.1b

13.8±3.1b

P<0.005

Glucagon AUC (ng x min/L)

1510±448

1090±448

1530±448

1177±448

418±448

P=0.424

Leptin AUC (ng x min/L)

33.2±36.3

17.6±36.3

97.3±36.3

30.3±36.3

67.9±36.3

P=0.506

HOMA

1.93±0.45

1.86±0.45

1.90±0.45

2.15±0.45

1.89±0.45

P=0.898

MFFM

8.22±0.22

8.27±0.22

8.49±0.22

8.17±0.22

8.27±0.22

P=0.055

Cederholm

69.7±6.2

64.6±6.2

68.7±6.2

68.0±6.2

64.5±6.2

P=0.719

* Least-square means ±SEM. AUC based on plasma concentrations at zero to 120 minutes.
† Within a row, values with different superscripts are significantly different (P<0.05)
‡ Equations utilized for insulin-resistant calculations obtained from cited references: HOMA, MFFM, Cederholm.

Other Findings

  • Peak glucose concentrations after both oat products and both barley products were significantly lower than that for glucose
  • Peak glucose responses within a grain (oat flakes vs. oat flour or barley flakes vs. barley flour) were not significantly different.
Author Conclusion:
  • Regardless of form, flour or flakes, oat and barley consumption reduces glucose and insulin responses
  • The higher soluble fiber content resulted in a smoother response curve, lower peak values and minimized the hypoglycemic effect that occurred three hours after a high-sugar meal
  • These results demonstrate that beneficial reductions in glucose and insulin can result if sufficient soluble fiber is consumed; they suggest that increasing the total oat or barley content of the American diet might lower the risk for type 2 diabetes.
Funding Source:
Government: USDA
Reviewer Comments:
  • No power calculation; don't know minimum detectable difference for flake vs. flour
  • No description of attrition
  • Barley flakes and flour and partial financial support were provided by ConAgra, Omaha, NE.
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? Yes
  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? Yes
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) Yes
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? Yes
  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%.) N/A
  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? Yes
  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? Yes
  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? N/A
  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)? N/A
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? Yes
  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? No
9. Are conclusions supported by results with biases and limitations taken into consideration? Yes
  9.1. Is there a discussion of findings? Yes
  9.2. Are biases and study limitations identified and discussed? Yes
10. Is bias due to study's funding or sponsorship unlikely? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.2. Was the study free from apparent conflict of interest? Yes