GDM: Carbohydrate (2016)


Grant SM, Wolever TMS, O'Connor DL, Nisenbaum R, Josse RG. Effect of a low glycaemic index diet on blood glucose in wowen with gestational hyperglycaemia. Diabetes Res Clin Pract. 2011, 91: 15-22.

PubMed ID: 21094553
Study Design:
Randomized Controlled Trial
A - Click here for explanation of classification scheme.
Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:
To determine the feasibility and effect on glycemic control of a low-glycemic-index (GI) diet in women with gestational diabetes or impaired glucose tolerance of pregnancy.
Inclusion Criteria:
  • Pregnant women 18 years to 45 years old
  • Gestational hyperglycemia.
Exclusion Criteria:
  • Multiple pregnancies
  • Acute or chronic illness affecting carbohydrate metabolism
  • T1DM or T2DM prior to current pregnancy
  • Use of insulin prior to giving informed consent
  • Over 34 weeks' gestation
  • Unable to communicate in English with no translator available.
Description of Study Protocol:
  • Recruitment: Referred to Diabetes in Pregnancy Clinic
  • Design: RCT
  • Blinding used: Physicians in the clinic
  • Intervention: Low-GI diet or control diet from 28 weeks' gestation until delivery.

Statistical Analysis

  • On intent-to-treat basis
  • Fasting and post-prandial glucose and post-prandial glucose increments were analyzed using linear mixed models
  • Number of self-monitored blood glucose (SMBG) values below, above and within target range recommend by the Canadian Diabetes Association were compared using chi-squared test
  • Maternal and infant birth weight were analyzed using standard multiple linear regression
  • Questionnaire data was examined as continuous variables with an independent T-test and displayed as frequencies and percents.
Data Collection Summary:

Timing of Measurements

  • Measurements began at 28 weeks and continued until delivery
  • Diet assessment every two weeks
  • SMBG baseline to Week Eight at fasting and two hours after breakfast, lunch and dinner
  • Blood at baseline and one month after intervention for fasting blood glucose (FBG) and HbA1c, insulin, lipids and C-reactive protein (CRP).

Dependent Variables

  • SMBG: Reviewed by clinic MD and noted in subject's chart. Collected for one week before intervention to represent baseline.
  • Serum glucose, HbA1c, insulin, lipids, CRP: Intravenous samples
  • Dietary intake: Three-day food records plus standardized open- and closed-ended questionnaire
  • Physical activity: Self log
  • Infant birth weight: Medical chart
  • Insulin data: Medical chart
  • Body weight: Subject medical chart.

Independent Variables
Low-GI or control diet.

Control Variables
Number of starch servings based on gestational energy requirement using exchange lists.

Description of Actual Data Sample:
  • Initial N: 47 females
  • Attrition (final N): 38
  • Age: 34 years.


  • South East Asian: 25%
  • Indian: 21%
  • Caucasian: 21% 
  • East Asian: 11% 
  • Caribbean: 4.9% 
  • Mixed: 6% 
  • Hispanic: 6% 


  • No significant differences in BMI, gestational age, HbA1c, fasting serum and blood lipids
  • The Control Group had a significantly higher FBG and CRP than intervention. 


Summary of Results:


  • Energy, protein, carbohydrate and fat intakes did not change significantly. Post-intervention, the Low-GI Group consumed significantly more dietary fiber than Control (30±1.6g and 23±1.0g, respectively; P=0.001) and had a significantly lower diet GI than Control (49±0.8g vs. 58±0.5g; P=0.001). The Low-GI Group had a significantly lower glycemic load than Control post-intervention (98.2±5.1 vs. 125±8.8; P=0.014). 
  • Fasting serum glucose fell by 0.20±0.07mmol per L (P=0.006) from baseline to one month, but there was no significant difference between the two groups. HbA1c did not change significantly during the study on either diet and there was no significant difference in fasting insulin, lipids or CRP between the two groups. 
  • There were no statistically significant differences between changes in fasting and mean post-prandial SMBG in Low-GI and Control. Fewer FBG were below target on Low-GI than Control (P=0.006). During treatment, the percentage of post-prandial glucose values on target increased from baseline by 6% (P<0.05) in controls, but by more than twice as much in Low-GI (13%; P<0.001). Significantly fewer post-prandial glucose values were above target on Low-GI than Control (25.9% vs. 30.3%; P=0.003).
  • Rate of maternal weight gain was not significantly different between groups. Infant birth weight was not significantly different between the two groups. 
  • There was no significant difference between groups for acceptability of the foods or symptoms.
Author Conclusion:
A low-GI diet was feasible and acceptable in this sample and facilitated control of post-prandial glucose. 
Funding Source:
Danone Institute of Canada
Reviewer Comments:
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? Yes
  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%.) Yes
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  4.4. Were reasons for withdrawals similar across groups? Yes
  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.) 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? 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? N/A
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? N/A
  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)? Yes
  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