DF: Cardiovascular Disease (2008)

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

To measure the effects on cholesterol metabolism and colonic functions of isolated citrus pectin in comparison with the same amount of pectic substances contained naturally in fruits and vegetables, and also with a comparable amount of fiber from wheat bran.

Inclusion Criteria:

University students (aged 18 to 28):

  • Apparently healthy, as judged by detailed questionnaire
  • Serum cholesterol less than 5.7mmol per L (220mg per dL)
  • Serum triglycerides less than 1.7mmol per L (150mg per dL)
  • Diastolic blood pressure less than 90mm Hg
  • Percent body fat less than 23% in males and 30% in females.
Exclusion Criteria:

None specified.

Description of Study Protocol:

Recruitment

University students in the Netherlands.


Design

  • Participants consumed a low-fiber control diet for 2.5 weeks and were divided into one of four diets varying in fiber content and source (see intervention below for description of diet groups) for the next five weeks
  • All food and drink were provided to participants except 100 discretionary calories per day
  • Measurements of cholesterol, intestinal transit time and blood pressure were collected before, following the low-fiber control diet and following the five-week diet
  • Group assignment method is unclear, except the authors specify groups were matched for initial serum cholesterol level, energy intake and sex.

Intervention 

62 participants consumed a low-fiber (14g per day) diet for 2.5 weeks and were divided into one of the following diet groups for five weeks:

  • Low-fiber (15g per day)
  • High-fiber rich in vegetables and fruits (41g per day) 
  • Diet supplemented with citrus pectin (24g per day)
  • Diet supplemented with wheat bran  (34g per day).

Statistical Analysis

  • Paired two-tailed T-test
  • Analysis of variance to test diet and sex effects on changes in parameters over the experimental period. If the diet effect was significant, a Tukey range test was used to compare group means.
Data Collection Summary:

Dependent Variables

  • Total and HDL-cholesterol: Fasting blood at study entry (two samples at one-day intervals averaged); during weeks two, three, four and five of the experimental period
  • Intestinal transit time, bile acids, fecal fat, electrolytes: Feces collected during the last seven days of both periods
  • Blood pressure: In seated position; timing not further specified.

Independent Variables

  • Nutrient intake measured using weighting plus questionnaire and Netherlands food composition tables:
    • Study entry for three days
    • During control period for two days
    • During intervention for five days
  • Each of the four intervention diets were also chemically analyzed in duplicate.

Control Variables

Sex.

Description of Actual Data Sample:
  • Initial N: 62 (40 male, 22 female)
  • Age: 18 to 28 years
  • Location: Wageningen University, The Netherlands.
Summary of Results:

 Key Findings

Change Over Experimental Period (Five Weeks)

Control (N=16)

Mean±SD, P-value

Vegetables/Fruit (N=15)

Mean±SD, P-value

Citrus Pectin (N=15)

Mean±SD, P-value

Bran (N=16)

Mean±SD, P-value

Dietary fiber intake, g per 1,000kcal 6.0 16.0 9.4 13.3
Total cholesterol 0.1±0.34, NS -0.17±0.63, NS -0.34±0.34, P<0.01 -0.34±0.41, P<0.01
HDL

0.01±0.12, NS

0.01±0.15, NS

0.02±0.18, NS

0.07±0.16, NS

Fecal wet weight (g per 24 hours)

-1±35, NS

89±0.37, P<0.01

89±34, NS

89±53, P<0.01

Fecal dry matter (g per 100g wet weight)

2±4, NS

-3±4, P<0.05

1±2, NS

-3±4, P<0.01

Frequency of stools per 24 hours

0.0±0.4, NS

0.2±0.3, P<0.05

0.0±0.4, NS

0.3±0.3, P<0.01

Mean transit time, hour

18±39, NS

-13±22,P<0.05

4±35,NS

-19±19,P<0.01

Other Findings

No significant differences in blood pressure for the experimental period. The control group had a 5mm Hg decrease in systolic blood pressure (P<0.10).

Author Conclusion:

It appears that some of the dietary fiber components of fruits and vegetables lower concentrations of serum cholesterol, while others can improve colonic function. Bran also has a favorable effect on colonic function, but in this short-term controlled study it increased serum cholesterol. Although the favorable effects of vegetables and fruits on serum cholesterol is small compared to the known effects of dietary fat and cholesterol, in uncontrolled conditions dietary fiber may indirectly reduce the concentration of serum cholesterol by displacing fat-rich products from the menu.

Funding Source:
Reviewer Comments:
  • Study population not well-described (for example, BMI)
  • Non-randomized design with intra-individual comparisons may have been a weaker design than a randomized trial with between group comparisons. Used paired T-test (appropriate for crossover designs) rather than ANOVA, which would have answered whether any of the fiber sources differentially affected outcome measures.
  • Unusual to see a cholesterol study without a measure of LDL and lasting less than six weeks
  • Mentioned good compliance in the discussion but didn't specify withdrawals or adherence measures.

 

 

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? No
  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? No
  2.4. Were the subjects/patients a representative sample of the relevant population? ???
3. Were study groups comparable? ???
  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? ???
  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? ???
  4.1. Were follow-up methods described and the same for all groups? ???
  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%.) ???
  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? ???
  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? ???
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? ???
  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? ???
  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? ???
  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? No
  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