AWM: Low Glycemic Diets (2006)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
To compare the effects of a low glycemic load diet with those of a diet based on Canada's Food Guide to Healthy Eating for People Four Years and Over on body weight, abdominal obesity, and lipid and glycemic control in cardiac rehabilitation patients.
Inclusion Criteria:
Older than 19 years of age with one or more of the following conditions:  postmyocardial infarction, postcoronary artery bypass surgery, postangioplasty, postunstable angina, stable coronary artery disease/angina, postaortic/postmitral valve surgery, cardiomyopathy, cardiac transplant, congestive heart failure or arrhythmia.
Exclusion Criteria:
Excluded if not included above.
Description of Study Protocol:

Recruitment

Not described - 4477 patients enrolled from 17 sites across Ontario.  All sites promoted Canada's Food Guide except 1 on low glycemic load diet.

Design

Cohort Study.

Blinding used (if applicable)

Not used.

Intervention (if applicable)

Patients advised to follow low glycemic load diet were compared with patients advised to follow principles of Canada's Food Guide to Healthy Eating for People Four Years and Over as part of the Ontario Cardiac Rehabilitation Pilot Project. 

Statistical Analysis

Baseline characteristics of subjects were compared by using the independent t test for continuous measures and Fisher's exact test for categorical measures.  The changes from entry to exit were also measured using independent t test.  Complete subject data were available for low glycemic load subjects, summary data for rest of Ontario.  Since overall Ontario project data included the low glycemic load subset, the values for the rest of Ontario were calculated by extracting the weighted influence of the low glycemic load subjects on the Ontario means and counts.  The sample size of the low glycemic load subjects was only used as the input for the degrees of freedom in the t tests.  The subset of low glycemic load subjects who had an assessment at one year after entry was used to demonstrate the maintenance of the changes.  Paired t tests were used to assess the significance of changes within subjects.  Linear regression was used to assess the association between the changes in use of statins, fibrates and fish oil, and the change in lipid and glycemic control parameters.

Data Collection Summary:

Timing of Measurements

Supervised 6-month program.  Baseline assessment completed with RN to collect date of birth, sex, smoking history, history of hypertension, dyslipidemia or diabetes, and medication (antiplatelet, antihypertensive, antidyslipidemic, and antihyperglycemic therapy).

Dependent Variables

  • Height measured to nearest 0.1 cm
  • Weight measured to nearest 0.1 kg
  • Abdominal circumference measured with subjects in standing position at level midway between iliac crest and the last rib
  • Heart rate and blood pressure measured according to 2004 Canadian recommendations
  • Blood drawn after 14 hour fast and analyzed for lipid profile (LDL, HDL, triglycerides), 75 g oral glucose tolerance test and HbA1c 

Independent Variables

  • Program had twice-weekly exercise classes, along with dietary counseling, behavior modification, lifestyle education, pharmacotherapeutic intervention and psychosocial and vocational counseling.  1800 kcal/day Canada Food Guide diet contains 55% of kcals from carbohydrate, 30% from fat, daily glycemic load of 140.  Low glycemic load diet designed to be isocaloric and contain 45% from carbohydrate to achieve daily glycemic load of 85.  Both diets were low in saturated fat (<10%) and cholesterol (<300 mg) with an emphasis on high fiber and monounsaturated fat.

Control Variables

 

Description of Actual Data Sample:

Initial N: 154 screened to follow low glycemic load diet, 1434 patients following Canada's Food Guide

Attrition (final N):  120 completed the low glycemic diet program.  15 patients did not qualify and 19 patients withdrew before study completion.  Follow-up data available on 96 of 120 patients. 

Age: Mean age low glycemic load:  63.6 years, rest of Ontario:  62.3 years

Ethnicity:  Not mentioned. 

Other relevant demographics: Not mentioned.

Anthropometrics:  Groups were well balanced with regard to baseline characteristics.  Incidence of diabetes was higher in the low glycemic load group.

Location: Canada

 

Summary of Results:

Other Findings

Patients on the low glycemic load diet lost more weight at 6 months (2.8 kg loss vs 0.2 kg gain, P < 0.0001), had a greater reduction in abdominal obesity (2.9 cm vs 0.4 cm, P < 0.0001), and had a greater improvement in HDL cholesterol (0.14 mmol/L vs 0.02 mmol/L, P < 0.0001), triglycerides (-0.44 mmol/L vs -0.08 mmol/L, P < 0.001) and glycemic control (fasting glucose -0.94 mmol/L vs 0.91 mmol/L, P = 0.0019).

After 1 year of follow-up, the low glycemic load patients had maintained (weight gain 0.7 kg, P = 0.21, triglycerides -0.07 mmol/L, fasting glucose -0.10 mmol/L and glycosylated hemoglobin A1c -0.18%, all not significant) or augmented (waist circumference -1.3 cm, P = 0.038; HDL cholesterol 0.08 mmol/L, P < 0.0001) the initial results.

Author Conclusion:
Implementation of a low glycemic load diet was associated with substantial and sustained improvements in abdominal obesity, cholesterol and glycemic control.  These results need to be confirmed in a randomized, blinded study.
Funding Source:
University/Hospital: Queens University (Canada)
Reviewer Comments:
Did not measure compliance with low glycemic load diet or measure actual glycemic load.  Only summary data was available for Ontario subjects.
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) N/A
  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? Yes
  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.) Yes
  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? 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%.) ???
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  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? N/A
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? N/A
  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.) N/A
  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? Yes
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? No
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? Yes
  6.6. Were extra or unplanned treatments described? Yes
  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? ???
  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? ???
  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? 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