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DM: Carbohydrates (2007)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
To determine whether a chronic low-glycemic index (LGI) diet, compared with a high-glycemic index (HGI) diet, has beneficial effects on plasma glucose control, lipid metabolism, total fat mass, and insulin resistance in type 2 diabetic patients.
Inclusion Criteria:
  • type 2 diabetes
Exclusion Criteria:
  • abnormal renal, hepatic or thyroid function
Description of Study Protocol:

Recruitment not specified - subjects volunteered

Design 

  • Subjects were randomly allocated to two periods of 4 weeks of an LGI or HGI carbohydrate diet separated by a 4-week washout interval, in a crossover design.

Blinding used (if applicable) not specified

Intervention (if applicable)

  • pre-study GI of diet estimated at 53 according to analysis of 3-day food records
  • during a 15-day run-in period subjects received individual counseling with a dietitian, who prescribed daily intake based on usual food intake patterns.
  • subjects were given diet sheets showing recommended intake of commonly used foods and a substitution list allowing exchanges within food groups.
  • Diet
    • LGI : items with a GI less than 45 recommended
    • HGI: foods with a GI higher than 60 recommended

Statistical Analysis

  • validity of the crossover design was tested by ANCOVA of the baseline results of the second period, with the baseline results of the first period as the covariable and the treatment of the first period as the main factor. 
  • the effects of the two diets were compared by mulitiple ANOVA followed by a post-hoc test (least significant difference).  The main factors in the analysis were
    • type of diet
    • time of assay
    • order of diets
  • the dietetic evaluations at the beginning and end of each period were compared two by two with a Student's paired t test.

 

Data Collection Summary:

Timing of Measurements

  • subjects hospitalized for testing for 2 days at the beginning and end of each diet period
  • during this period the meals were the same as for that diet period
  • blood samples collected at time 0 (fasting) at hourly thereafter for 8 hours
  • during the second day three blood samples were taken with 5-min intervals to measure the homeostasis model asssessment

Dependent Variables

  • glucose dynamics
  • homeostasis model assessment
  • plasma glucose by glucose oxidase method
  • plasma insulin by radioimmunoassay
  • plasma lipids
  • plasma apo B by immunochemical assay
  • plasminogen activator inhibitor
  • euglycemic-hyperinsulinemic clamp studies

Independent Variables

  • low glycemic index vs high glycemic index diet
  • all therapies continued unchanged throughout the study
  • dietary compliance assessed with food record kept by subjects on the last 7 days of each period

 Control Variables

 

Description of Actual Data Sample:

Initial N: 12 men

Attrition (final N):  12

Age: 54±2 y

Ethnicity: not specified

Other relevant demographics:

  • none of the subjects treated with insulin
  • mean fasting glycemia 8.7±0.7 mmol/l

Anthropometrics

  • mean body weight 93±3 kg
  • mean BMI 31±1

Location: France

 

Summary of Results:

Results of the 7-day food records were unchanged at the end of the dietary period except for fiber, which was significantly lower on the HGI diet (P<0.0001).

GI was significantly different between the two diets (P<0.0001).

Variables

HGI diet

  

LGI diet

  
  Baseline 4 weeks Baseline 4 weeks

Fasting Glycemia, mmol/l

 9.4±0.5

 

 9.8±0.6 

 10.1±0.8*

 

  9.19±0.7**€§

Morning Peak Glycemia, 60-0 min

 4.2±0.3*

  3.7±0.3*

 2.80±0.3**

  3.3±0.5**€

Glucose AUC

 527±57*

  520±61*

 358±90**

  274±32**€
Fasting insulinemia, pmol/l  113±11  125±16 111±19  123±22
Morning peak insulinemia, 60-0 min  142±15  171±19  126±25  149±27
Insulin AUC  845±10*  754±27  646±36**  618±65€
HbA1c, %  7.45±0.35  7.57±0.35*  7.56±0.36*  7.17±0.39**€§

 *Data followed by (*) and (**) for a row are significantly different at P<0.05

**see above

€ P<0.05 by multiple ANOVA

§P<0.01 fpr change

Other Findings

Basal and insulin-mediated glucose metabolism

  • whole body periperal insulin sensitivity was significantly higher after the LGI diet than after the HGI diet (P<0.001).
  • No change in hepatic glucose production in the fasting state between the two dietary periods
  • insulin secretion and sensitiveity determined by HOMA remained unchanged during the two dietary periods

Plasma Lipids

  • no significant change in triacylglycerol levels
  • total and LDL cholesterol decreased during the LGI period (P<0.05)

Plasma activator inhibitor activity decreased on the LGI diet (P<0.05)

 

Author Conclusion:
This study provides evidence of the chronic utility of LGI diets and clearly demonstrates the capacity of this type of diet to significanlty improve plasma glucose control, whole-body glucose utilisation, plasma FFAs, total and LDL cholesterol and PAI-1 levels.
Funding Source:
Reviewer Comments:
Small sample size but homogeneous group - authors note that the presence of women in other studies might increase within-subject variations.
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? No
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? N/A
  4.1. Were follow-up methods described and the same for all groups? N/A
  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? N/A
  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? Yes
  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)? 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