DF: Cardiovascular Disease (2008)

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

To compare the effects of oat-bran fiber and wheat bran fiber on healthy patients who had undergone a colonoscopy with and without polypectomy.

Inclusion Criteria:
  • Volunteers with normal colon
  • Volunteers with history of previous polypectomy.
Exclusion Criteria:

Not described

Description of Study Protocol:

Recruitment

45 volunteers (31 men and 14 women aged 61.3±1.6 years, (mean ± SE, range 30-79 years) with a history of previous polypectomy (27±2.8 months previously) and 49 volunteers (26 men and 23 women aged 51.2±1.8 years) who were found to have a normal colon on colonic examination. 

Design

Metabolically controlled, parallel, double-blind study designed to ensure that the only important variable was a difference in fiber type.

Intervention

The subjects in the polyp and non-polyp groups were randomly assigned to the two arms:

  • The experimental arm received a supplement of oat bran twice per day
  • The control arm received a supplement containing wheat bran twice per day. 

The intervention lasted 14 days during which the volunteers were provided with a defined diet delivered to their homes. 

Patients visited the clinic twice after an overnight fast: at the start and at the end of the 14-day diet. At each visit to the clinic, patients provided fecal samples collected over the previous 48 hours and immediately frozen, a breath sample, and 30ml of blood. 

A three-day food record was also obtained at the initial visit and was analyzed by use of nutrient composition tables. 

During the two-week intervention period when the subjects were given complete diets, they checked off the food they consumed on the menu plans. Compliance was assessed by comparing the composition of the foods consumed according to the subjects' records with that of the prescribed diets provided. 

  • Volunteers took either wheat bran mixed with cream of wheat or oat-bran supplements at 1.6µg dietary fiber/J (6.8g dietary fiber per 1,000kcal) to a minimum of 16.4g fiber per day 
  • Supplements were taken with both breakfast and dinner as hot of cold cereals 
  • The basic diet to which these supplements were added was similar for both treatments and was fed in a three-day rotating menu taking into account specific food preferences of the volunteers 
  • The diets were fed at one of four energy amounts: 6.8, 8.4, 10.0, and 11.7MJ (1,600, 2,000, 2,400, and 2,800kcal). Volunteers were fed the amount closest to their requirements based on the Lipid Research Clinics tables. 
  • The macronutrient profile of the diets as prescribed were 37% fat, 16% protein, and 47% carbohydrate and were modeled on the recorded intake of similar patients in previous nutritional studies 
  • The bran supplements represented a mean of 12.8% of the total dietary energy 
  • The wheat-bran diet was supplemented with cream of wheat and additional cheddar cheese to achieve the desired macronutrient profile. 

Statistical Analysis

  • Mean ± SE 
  • T test
  • Analysis of covariance with adjustment for baseline values and gender.
Data Collection Summary:

Timing of Measurements

Patients visited the clinic twice after an overnight fast: at the start and at the end of the 14-day diet. At each visit to the clinic, patients provided fecal samples collected over the previous 48 hours and immediately frozen, a breath sample, and 30mL of blood. A three-day food record was also obtained at the initial visit and was analyzed by use of nutrient composition tables. 

Dependent Variables

  • Variable 1: Total cholesterol (mmol/L) measured using the Lipid Research clinics protocol in a laboratory that was certified as specified for standardization by the Centers for Disease Control (Atlanta, National Heart, Lung, and Blood Institute lipid standardization program)
  • Variable 2: LDL cholesterol (mmol/L) calculated by using the formula of Friedewald et al 
  • Variable 3: HDL cholesterol (mmol/L) measured using the Lipid Research clinics protocol in a laboratory that was certified as specified for standardization by the Centers for Disease Control (Atlanta, National Heart, Lung, and Blood Institute lipid standardization program)
  • Variable 4: Triglycerides (mmol/L) measured using the Lipid Research clinics protocol in a laboratory that was certified as specified for standardization by the Centers for Disease Control (Atlanta, National Heart, Lung, and Blood Institute lipid standardization program)
  • Variable 5: Apolipoprotein A-1 (g/L) measured by a standard enzyme-linked immunosorbent assay (ELISA) technique with a modified coating buffer and timing of individual steps to allow each assay to be completed in one day
  • Variable 6: Apolipoprotein B (g/L) measured by a standard enzyme-linked immunosorbent assay (ELISA) technique with a modified coating buffer and timing of individual steps to allow each assay to be completed in one day.

Independent Variables

Diet composition (either supplemented with oat bran or wheat bran) measured by three-day food record, nutrient composition tables, diet lists to check off the food they consumed on the menu plans.

Control Variables

  • Baseline values
  • Gender.
Description of Actual Data Sample:
  • Initial N: N=94
    • 45 volunteers with a history of previous polypectomy
      • 31 men
      • 14 women
    • 49 volunteers with a normal colon upon examination
      •  26 men
      •  23 women
  • Attrition (final N): Final n=84
    • Experimental group (oat bran) =42
      • 29 men
      • 13 women
    • Control group (wheat bran) =42
      • 21 men
      • 21 women
  • Age:
    • Experimental group (oat bran) =55.1±2.0 years
    • Control group (wheat bran) =56.6±2.0 years
  • Ethnicity: Not reported
  • Anthropometrics:
Characteristics Control (wheat bran) Experimental (oat bran)
Weight (kg) 75.5±2.2 73.8±1.9
Height (m) 1.69±0.01 1.70±0.02
BMI (kg/m2) 26.2±5 25.1±0.4
Postpolyp/Non-polyp 18/24 21/21
  • Location: Not reported.

 

Summary of Results:

Results

The randomization process let to two group with comparable age, gender, body mass index, and number of postpolypectomy subjects. The overall mean body weight change after the two-week intervention was -0.65±0.13kg (median -0.5kg). Two subjects lost >5% and <10% of their initial body weight. The difference in weight change between the oat (-0.66±0.20kg) and the wheat group (-0.63±0.16kg) was not significant. 35 subjects (19 of the oat group and 16 of the wheat group) had no symptoms. 37 (18 on oat and 19 on wheat) had mild symptoms, and 12 (five on oat and seven on wheat) had moderate symptoms with some bloating and loose feces. No one complained of severe symptoms such as diarrhea or severe cramping. 

The 84 subjects consumed an estimated 91% of their calories from the diet. 43 consumed >90% of the designated supplement and diet. Pre-intervention diet records showed a similarity between groups in their energy, macronutrient, and fiber intakes, although carbohydrate in the pre-intervention diet was marginally higher in the oat-bran group (246 vs. 217 grams per day, P=0.002). 

Pre-intervention and Intervention Diet Composition

  Pre-intervention Intervention
  Control group
(wheat bran)*
Experiment group
(oat bran)*
Control group
(wheat bran)*
Experiment group
(oat bran)*
Energy        
 MJ 7.90±0.38  8.31±0.33  8.18±0.21  8.60±0.24 
 Kcal 1,888±91  1,986±78  1,955±51  2,060±57 
Protein (g) 80±3  82±3  79±2  85±2 
Fat (g)        
Total 73±2  72±2  81±2  84±2 
Saturated Fatty Acids 27±2  28±2  32±1  31±1 
Polyunsaturated Fatty Acids 12±2  12±2  16±1   
Carbohydrate        
Available (g) 217±7  246±||  234±6  246±7 
Fiber (g) 15±1  17±1  24±1  25±1 
Cholesterol (mg) 292±14  288±17  283±7  285±10 
Alcohol (g)     0.2±0.1  0.4±0.2 
Energy consumed (%)     90±1  93±2 
Supplement consumed (%)     94±2  95±2 

 

* mean ± SE

|| significantly different from pre-intervention control group (wheat bran), P=0.002

The initial total cholesterol concentration of the oat group was higher than that of the wheat group and the initial LDL cholesterol and apolipoprotein B concentrations were also higher in the oat group. There were no significant differences in the initial HDL cholesterol, triglycerides, and apolipoprotein A-1 between the two groups. 

The mean total cholesterol concentration decreased significantly in both groups. However, the decrease of the oat group was significantly greater than that of the wheat group. The mean total cholesterol concentration decreased by 10.8% in the oat group and by 4.7% in the wheat group (P=0.001). The mean LDL cholesterol and apolipoprotein B concentrations also decreased more markedly in the oat-bran supplemented group. Triglycerides and apolipoprotein A concentrations were unchanged by the intervention. After adjustment for baseline values and gender, the significant differences between oat and wheat treatments remained and the adjusted mean decreases in total cholesterol were 0.56±0.08 and 0.29±0.08mmol/L for the oat and wheat bran supplements, respectively (P=0.022). The corresponding values for LDL cholesterol were 0.39±0.07 and 0.15±0.07mmol/L (P=0.024) whereas for apolipoprotein B the decrease on oats was 0.102±0.023g/L and on wheat was 0.044±0.023g/L (P=0.081). Without adjusting for gender in the GLM model, the differences in apolipoprotein B were 0.111±0.023g/L on oats and 0.045±0.023g/L on wheat (P=0.048).

 

Variable and intervention Before After Change
Total cholesterol (mmol/L)      
 Wheat bran (n=42) 5.36±0.14  5.11±0.14a  -0.25±0.07 
 Oat bran (n=42) 5.88±0.17c  5.24±0.16a  -0.63±0.09 
LDL cholesterol (mmol/L)      
 Wheat bran (n=41) 3.34±0.12  3.23±0.13b  -0.11±0.06 
 Oat bran (n=42) 3.86±0.16e  3.38±0.15 -0.48±0.09d 
HDL cholesterol (mmol/L)      
 Wheat bran (n=42) 1.46±0.06  1.35±0.05 -0.11±0.02 
 Oat bran (n=42) 1.42±0.06  1.28±0.04 -0.14±0.04 
Triglycerides (mmol/L)      
 Wheat bran (n=42) 1.22±0.10  1.15±0.09  -0.07±0.06 
 Oat bran (n=42) 1.37±0.12  1.32±0.13  -0.05±0.04 
Apolipoprotein A-1 (g/L)      
 Wheat bran (n=37) 1.403±0.060  1.289±0.050 -0.132±0.021 
 Oat bran (n=36) 1.373±0.042  1.234±0.035 -0.139±0.020 
Apolipoprotein B (g/L)      
 Wheat bran (n=37) 0.964±0.038  0.912±0.039  -0.035±0.018 
 Oat bran (n=36) 1.077±0.051f  0.956±0.049a  -0.121±0.028

a Significantly different from Before, P<0.001

b Significantly different from Before, P=0.030

c Significantly different from Wheat bran, P=0.02

d Significantly different from Wheat bran, P=0.001

e Significantly different from Wheat bran, P=0.01

f Significantly different from Wheat bran, P=0.04

 

Author Conclusion:

We conclude that oat bran has an advantage over wheat bran in lowering serum lipids. We have used large numbers of individuals with mean serum cholesterol concentrations above the desirable range (<5.2mmol/L) who were tested on metabolic diets. The advantage gained was relatively small, approximately 5%, and may be missed in smaller studies or where individuals with low blood lipids are studied. Nevertheless, even a 5% decrease in serum cholesterol may translate into a 10% decrease in cardiovascular mortality and thus soluble fiber may make a useful contribution to a lipid-lowering diet.

Funding Source:
Reviewer Comments:
  • Minimal description of study population, reasons for attrition, effect of attrition on results
  • Blinding mentioned initially but never described in detail.
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) ???
 
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? No
  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? No
  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%.) No
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? No
  4.4. Were reasons for withdrawals similar across groups? ???
  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? Yes
  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? No
  6.6. Were extra or unplanned treatments described? No
  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? 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)? No
  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? N/A
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