AWM: Low Glycemic Diets (2006)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
To assess the impact of low glycemic index diets on traditional cardiac risk factors in people with established coronary disease, and to investigate whether volunteers were able to change the glycemic index of the diet in the home situation following advice, rather than supplying food products to them.
Inclusion Criteria:
Male and female free-living patients with coronary heart disease between ages 30 - 70 years.  CHD inclusion criteria:  myocardial infarction (chest pain associated with ECG evidence of myocardial infarction and/or elevated cardiac enzymes); unstable angina (cardiac pain associated with dynamic ECG abnormalities; or angiographically proven coronary artery disease (>50% stenosis in 1 or more major epicardial vessels in multiple projections).
Exclusion Criteria:

Cardiomyopathy, serious organ disease, systemic illness, chronic alcohol abuse, serious psychiatric illness, poor compliance with 7-day food diary of habitual diet or failed medical screening.

Description of Study Protocol:

Recruitment

All volunteers selected from cardiac intervention database listing those who have had CABG or cardiac angioplasty between 1997 - 1998.  All received a letter inviting them to participate and to reply in writing using prepaid envelope. 

Design

Randomized parallel group trial.  Randomization carried out using random numbers.

Blinding used (if applicable)

Not used.

Intervention (if applicable)

Assigned to control group or low glycemic index intervention group for 12 weeks.

Statistical Analysis

Power analysis based on data from other intervention studies.  All data checked for normality and presented as mean with s.e.m. unless otherwise stated.  Statistical comparison within or between groups was made using ANOVA with a Bonferroni post hoc analysis and chi-square as appropriate.

Data Collection Summary:

Timing of Measurements

All outcome measures assessed at baseline and after 12 weeks.  Each subject visited hospital on 5 occasions over 12 weeks of study. 

Dependent Variables

  • Height measured using wall-mounted stadiometer without shoes to nearest cm
  • Weight taken in light clothing on digital scales accurate to 100g
  • Waist circumference measured to EEC guidelines
  • Blood pressure measured using standard methodology taking average of 3 readings
  • Fasting glucose, insulin, total cholesterol, HDL-cholesterol, VLDL-cholesterol, LDL-cholesterol and triglycerides measured using standard methods

Independent Variables

  • Control group received healthy eating dietary advice only (50% carbohydrate, 35% fat, <10% saturated fat, 10% PUFA and 15% monounsaturated fat.  The intervention group received healthy eating advice emphasizing low glycemic index carbohydrates (glycemic index < 85).  All nutritional advice given on an individual basis through regular visits and telephone calls.  All patients with BMI >28 were advised to lose weight at rate of 1 kg/month.  Subjects kept 7-day diet diary on 4 occasions and was validated against estimated EE using Schofield's equation.  Nutritional content calculated using DietPlan 5 and glycemic index calculated using international table of glycemic index.

Control Variables

 

Description of Actual Data Sample:

Initial N: 60 respondents and 57 met inclusion criteria.

Attrition (final N):  55 completed, 49 male, 6 female.  29 in Healthy Eating and 26 in Low Glycemic Index group.  2 dropouts not discussed.

Age:  Healthy eating:  61.8 +/- 9 years, Low glycemic index:  63.6 +/- 9.4 years 

Ethnicity:  Not mentioned. 

Other relevant demographics:

Anthropometrics Despite randomization, statistically more of the healthy eating group than the low glycemic index group were taking an aspirin and a statin.

Location:  United Kingdom 

 

Summary of Results:

 

LGI - 0 wks LGI - 12 wks Healthy - 0 wks Healthy - 12 wks

P value

Energy (kcal) 2105 +/- 91 2033 +/- 113 2090 +/- 104 1759 +/- 79 0.0429
GI 81+/- 2 71 +/- 1 82 +/- 2 81 +/- 1 0.0001
GI Load 195 +/- 9 164 +/- 11 176 +/- 10 152 +/- 9 0.0178
Weight (kg) 81.2 +/- 2.5 79.8 +/- 2.3

81.7 +/- 3.1

79.6 +/- 2.8

0.9345

Other Findings

Aim of the study was to induce a 20% drop in glycemic index, but a decrease of only 13% was achieved.  A significant lower dietary glycemic index was achieved in the group assigned to a low glycemic index diet compared to the healthy eating control group (71 +/- 1 vs 81 +/- 1, p = 0.0001). 

Fibre intake was also higher in the low glycemic index group (20 +/- 1 vs 15 +/- 1 g, p = 0.0059).

All biochemical markers of glucose and lipid metabolism measured were similar after 12 weeks of the low glycemic index diet or control diet.

Author Conclusion:
The low glycemic index group achieved a significant low glycemic index and a higher dietary fibre intake.  In people with preexisting coronary disease, whose cardiovascular risk factors are managed by polypharmacy, it was not possible to detect any additional benefit of low glycemic index diet above the healthy eating intervention.
Funding Source:
University/Hospital: Hammersmith Hospital, Kings College
Reviewer Comments:

Targeted drop in GI not achieved.  Subjects were taking medications.  Low dropout rate. 

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? ???
  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? ???
  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? No
  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.) No
  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? 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? 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? 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