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Glycemic Index (2016)

Citation:
Moses RG, Barker M, Winter M, Petocz P, Brand-Miller JC. Can a low-glycemic index diet reduce the need for insulin in gestational diabetes mellitus? A randomized trial. Diabetes Care. 2009; 32(6): 996-1000.
 
Study Design:
Randomized Controlled Trial
Class:
A - Click here for explanation of classification scheme.
Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:
To examine whether a low–glycemic index diet used as MNT for women with GDM could result in a reduced need for insulin use during pregnancy with no compromise of obstetric and fetal outcomes.
Inclusion Criteria:
  • Age 18 years to 40 years 
  • Singleton pregnancy
  • No previous GDM
  • Non-smoker
  • Diagnosis of GDM and seen for the first dietary visit between 28 and 32 weeks of gestation
  • Ability to follow the protocol requirements
  • Written informed consent was given.
Exclusion Criteria:
  • Age less than 18 years or older than 40 years
  • Previous GDM
  • Smoker
  • Inability to follow the protocol requirements
  • Any condition or medication that could affect glucose levels
  •  Unwillingness to follow the prescribed diet.
Description of Study Protocol:

Recruitment

  • All pregnant women who tested positive for gestational diabetes were considered for the study
  • Recruitment lasted over a 12-month period (October 2007 to September 2008) and was completed at the Diabetes Center.

Design

  • Randomized controlled trial
  • Women were randomly assigned to receive one of two different diets using permuted blocks of unequal size with the list generated using STATA (version 7.0).

Blinding used

  • Study dietitians were not blinded to dietary assignment but were aware of the need for impartiality and equivalent treatment
  • Physician caring for the patients was not informed of the diet allocation.

Intervention

  • Women were randomly assigned to a specific diet:
    • Both diets were compatible with the recommended nutritional intake in pregnancy
    •  CHO intake designed to achieve a minimum of 175g per day with only the recommended choice of CHO foods varying
    • The dietary advice was individualized with specific mention of the energy and nutrient balance to achieve normal weight gain during the third trimester.
  • Low-glycemic index diet:
    •  Based on previously verified low-glycemic index food including pasta, grain breads and unprocessed breakfast cereals with a high fiber content
    • Women were specifically asked to avoid consuming white bread, processed commercial breakfast cereals, potatoes and some rice varieties.
  • Conventional, higher-glycemic index diet group:
    •  Advised to follow a diet with a high-fiber and low-sugar content, with no specific mention of the glycemic index
    • Potatoes, whole wheat bread and specific high-fiber, moderate-glycemic to high-glycemic index breakfast cereals were recommended.
  • During clinic visits, the dietitian referred to the diets as the low-glycemic index diet or the high-fiber and low-sugar diet
  • Participants were provided with a booklet outlining the CHO choices as well as the CHO food amounts constituting one serving (based on 15g portions)
  • Participants were advised to consume three small meals and two to three snacks with a specified number of servings of CHO
  • Blood glucose control:
    • Home glucose meters were provided and women were asked to test after fasting and one hour after the start of each of their three major meals at least every second day
    • Use of insulin, unless there were exceptional circumstances, was advised if more than once a week the fasting glucose was 5.5mmol per L or more or the one-hour postprandial glucose was 8.0mmol per L or more
    • For women consuming the low-glycemic index diet who exceeded these values, insulin was started immediately
    • Women consuming the higher-glycemic index diet who exceeded these values were changed to a low-glycemic index diet, and their responses were reviewed over a week
    • When indicated, insulin treatment was initiated with twice-daily pre-mixed insulin and dose adjusted regularly to achieve glycemic goals.

Statistical Analysis

  • Independent sample T-tests were used to compare the dietary components and the glycemic index, glycemic load and CHO values of the low-glycemic index and the high-glycemic index groups at the various appointment times
  • Pearson X2 tests of independence were used to compare proportions identified as needing insulin and actually starting on insulin in the low-glycemic index and high-glycemic index groups
  • SPSS (version 14; SPSS, Chicago, IL) was used
  • Results were considered significant if P<0.05.

 

Data Collection Summary:

Timing of Measurements

  • Initial food record was completed before the first visit with the dietitian between 28 and 32 weeks of gestation
  • Visits two and three were conducted approximately one to two and approximately three to four weeks, respectively, after the initial visit
  • Final visit was at 35 weeks to 37 weeks of gestation.

Dependent Variables

  • Food records:
    • Three-day records completed at baseline
    • Seven-day records completed at visits two and three
    • Three-day record completed at final visit
    • Glycemic index was calculated as the sum of the weighted glycemic index of all CHO foods in the diet, with the weighting proportional to the contribution of each food to the total CHO intake.
  • Use of insulin: Advised if more than once a week the fasting glucose was 5.5mmol per L or more or the one-hour postprandial glucose was 8.0mmol per L or more.

Independent Variables

Nutrition counseling on either low-glycemic index diet or high-fiber and low-sugar diet.

Control Variables

  • Maternal weight: Measured to the nearest 0.1kg on floor scales with subjects dressed in light clothes and without shoes
  • Maternal height: Measured to the nearest 0.1cm against a wall using a non-stretchable fiberglass measuring tape
  • Obstetric outcomes were obtained from medical record:
    • Birth weight
    • Fetal length and head circumference
    • Apgar score
    • Method of delivery.
Description of Actual Data Sample:

 

  • Initial N: N=212 women were eligible for the study; of these, 63 met inclusion criteria and agreed to participate
  • Attrition (final N): N=31 low-glycemic group; N=32 high-glycemic group.

Age

  • Low-glycemic group: 30.8±0.7
  • High-glycemic group: 31.3±0.8.

Ethnicity

All women except one were Caucasian.

Other Relevant Demographics

  • Parity:
    • Low-glycemic group: 0.84±0.17
    • High-glycemic group: 0.78±0.18.

Anthropometrics

  • Weight at enrollment (kg):
    • Low-glycemic group: 83.1±3.2
    • High-glycemic group: 86.9±3.6.
  • BMI at enrollment (kg/m2):
    • Low-glycemic group: 32.0±1.2
    • High-glycemic group: 32.8±1.4.

Location

Wollongong, New South Wales, Australia.

 

Summary of Results:

Key Findings

  • Women meeting criteria to start on insulin:
    • Low-glycemic group: Nine of 31 (29%)
    • High-glycemic group: Nineteen of 32 women (59%); P=0.023
    • After switching to low-glycemic index diet: Ten of 32 (31%), not significantly different from original low-glycemic group.
  • Timing of insulin initiation
    • Low-glycemic group: 32.1±0.4 weeks
    • High-glycemic group: 32.3±0.5 weeks (P=0.83).

Other Findings

Food records:

  • Baseline: No significant differences with respect to energy (P=0.50) and most nutrients except for a higher percentage of energy from protein in the high-glycemic index group (P<0.009)
  • Between the baseline and final visits:
    •  Significant reduction in total energy consumed in both groups due mainly to a reduction in the CHO intake: No significant differences in the extent of this reduction between the two groups
    • Amount of protein consumed as a percentage of energy intake increased significantly for both groups
    •  Percentage of energy intake for monounsaturated fats, polyunsaturated fats and saturated fats was not significantly different between the groups and did not change during the study.
 
  Low-glycemic Index Group High-glycemic Index Group, No Insulin High-glycemic Index to Low-glycemic Index Group P-value* P-value†
N 31 31 (final 12) 19 (final 18)    
Energy (kcal)
Baseline visit 1,994±72 1,932±146 1,914±88 0.50 0.91
Final visit 1,713±66 1,664±79 1,651±73 0.63 0.91
Change (P-value‡) −281±79 (0.001) −251±140 (0.10) −262±119 (0.042)    
Protein (percent energy)
Baseline visit 18.4±0.6 20.9±1.3 21.7±1.2 0.009 0.64
Final visit 23.9±0.7 23.5±0.8 24.4±0.7 0.51 0.41
Change (P-value‡) +5.5±0.9 (<0.001) +2.2±1.1 (0.070) +2.7±1.2 (0.041)    
Carbohydrate (percent energy)
Baseline visit 45.0±1.0 42.2±1.1 45.1±2.0 0.50 0.28
Final visit 36.7±1.1 37.8±1.1 35.1±1.5 0.80 0.21
Change (P-value†) −8.3±1.1 (<0.001) −4.3±1.3 (0.006) −10.4±2.5 (<0.001)    
Fat (percent energy)
Baseline visit 31.7±0.8 32.5±1.3 31.7±1.7 0.81 0.74
Final visit 33.4±1.1 34.0±1.2 34.5±1.8 0.57 0.79
Change (P-value‡) +1.7±1.0 (0.11) +1.6±1.7 (0.36) +3.0±2.2 (0.19)    
Fiber (g)
Baseline visit 25.4±1.3 23.1±1.2 24.0±1.5 0.30 0.66
Baseline visit 25.6±1.3 22.9±1.1 22.3±1.6 0.13 0.77
Change (P-value‡) +0.3±1.4 (0.86) +0.3±1.5 (0.84) −1.9±1.7 (0.28)    


 

  • Data are means ±SEM

  • *Comparison of low-glycemic index group with high-glycemic index group (high-glycemic index groups combined)

  • †Comparing those who changed to a low-glycemic index diet with those continuing to consume a high-glycemic index diet

  • ‡Comparisons from baseline to final visit (for those with baseline and final visits only).


Glycemic Index

 

  High-glycemic Index Group      
Low-glycemic Index Group Did Not Meet Criteria for Insulin Use Met Criteria for Insulin Use and Changed to Low-glycemic Index Diet P-value* P-value†  
N 31 13 19    
Baseline visit 57.3±0.9 57.9±1.5 57.4±1.2 0.83 0.79
Visit Two 49.2±0.9‡ 56.9±1.1 57.9±1.0 <0.001 0.53
Visit Three 48.7±0.9‡ 58.2±0.7§ 52.2±1.4§ <0.001 <0.001
Final visit 48.0±0.9 56.0±1.1§ 49.6±1.1§ 0.018 <0.001
Change: Baseline to final visit (P value) −8.4±1.0 (<0.001) −1.5±1.6 (0.38) −7.9±1.1 (<0.001)    
 

  • Data are means ±SEM

  • *Comparison of low-glycemic index with high-glycemic index groups (combined)

  • †Comparing those who changed to a low-glycemic index diet with those continuing to consume a high-glycemic index diet

  • ‡N=30

  • §N=12.


Birth outcomes:

  • No significant differences between groups with respect to weight gain from baseline to delivery, induction of labor, method of delivery or gestational age at delivery
  • For women in the low-glycemic index group, the birth percentile (46.3±5.0) and ponderal index (2.7±0.05) were not significantly different from the birth percentile (54.3±4.8, P=0.25) and ponderal index (2.6±0.04, P=0.12) for women in the high-glycemic index diet group
  • Three women in both groups had a large-for-gestational-age baby (90th percentile or more), and two women in the low-glycemic index group had a small-for-gestational-age baby (10th percentile or less)
  • There were no significant differences with respect to induction of labor, method of delivery, fetal percentile and ponderal index who were and were not receiving insulin.
Author Conclusion:
A low-glycemic index diet for women with GDM is safe, well tolerated and sustainable. A low-glycemic index diet significantly reduces the need for the use of insulin without compromise of obstetric or fetal outcomes.
Funding Source:
University/Hospital: University of Sydney, Illawarra Diabetes Service
Reviewer Comments:
One of the study authors is also a co-authors of The New Glucose Revolution book series; President of the GI Foundation, a nonprofit glycemic index–based food endorsement program in Australia; and Director of the University of Sydney glycemic index testing service.
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? 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? 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.) 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? 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? ???
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.2. Was the study free from apparent conflict of interest? No