EAL

Glycemic Index (2016)

Citation:

Louie JCY, Markovic TP, Perera N, Foote D, Petocz P, Ross GP, Brand-Miller JC. A randomized controlled trial investigating the effects of a low-glycemic index diet on pregnancy outcomes in gestational diabetes mellitus. Diabetes Care, 2011, 34: 2,341-2,346.

PubMed ID: 21900148

Study Design:

Randomized Controlled Trial

Class:

A - Click here for explanation of classification scheme.

Quality Rating:

POSITIVE: See Quality Criteria Checklist below.

Research Purpose:

To investigate the effect of a low-glycemic index (LGI) vs. a conventional high-fiber diet on pregnancy outcomes, neonatal anthropometry and maternal metabolic profile in gestational diabetes mellitus (GDM).

Inclusion Criteria:

Women 18 years to 45 years of age
20 to 32 weeks gestation
Diagnosis of GDM by a 75-gram oral glucose tolerance test
Healthy singleton pregnancy.

Exclusion Criteria:

Special dietary requirements
Pre-existing diabetes
Pregnancy achieved by assisted reproduction
Smoked or used alcohol during pregnancy.

Description of Study Protocol:

Recruitment: Women who met inclusion/exclusion criteria between September 2008 and November 2010
Design: Randomized controlled trial
Blinding used: All study personnel except the dietitian were blinded to dietary assignment.

Intervention

One of two diets of similar protein (15-25%), fat (25-30%) and carbohydrate (40-45%) content, but one with an LGI (target GI at least 50) and the other with a high-fiber content and moderate GI, similar to the Australian average (HF, target GI approximately 60)
Both provided all essential nutrients for pregnancy other than iron and iodine, which were supplemented by treating endocrinologist
Baseline three-day diary provided information on baseline dietary composition and was the basis of of individualized dietary counseling.

Statistical Analysis

Pearson X² test was used to test for differences between groups for categorical data and continuous data were tested using on-way ANOVA
Paired T-test was used to assess within group changes from baseline to final outcomes.

Data Collection Summary:

Timing of Measurements
Baseline and approximately 36 weeks gestation.

Dependent Variables

Birth weight, infant length, infant head circumference and need for emergency cesarean section: Medical records.
Blood glucose, insulin, HOMA2-IR, fructosamine, HbA1c: Blood.

Independent Variables
One of two diets of similar protein (15-25%), fat (25-30%) and carbohydrate (40-45%) content, but one with an LGI (target GI at least 50) and the other with a high-fiber content and moderate GI, similar to the Australian average (HF, target GI approximately 60).

Control Variables

Both provided all essential nutrients for pregnancy other than iron and iodine, which were supplemented by treating endocrinologist
Baseline three-day diary provided information on baseline dietary composition and was the basis of of individualized dietary counseling
Subjects attended three face-to-face visits with he study dietitian
A 24-hour dietary recall was done at each visit to assess compliance.

Description of Actual Data Sample:

Initial N: 99 females
Attrition (final N): 92 (LGI, 47; HF, 45)
Age: 26 years to 42 years
Ethnicity: 59.6% Asian, 31.9% Caucasian and 8.5 other in LGI. 55.6% Asian, 40.0% Caucasian and 4.4% other in HG.
Other relevant demographics: LGI group had significantly higher two-hour post-load blood glucose levels (P=0.024) but was otherwise similar to HF
Anthropometrics: Pre-pregnancy BMI 23.9±4.4 in LGI and 24.1±5.7 (NS)
Location: Sydney, Australia.

Summary of Results:

Other Findings

LGI Group had a significantly lower GI and Gl than the HF Group (both P<0.001)
Intake of fat, fiber, calcium, iron, zinc and folate significantly increased in LGI Group. HF Group had increased energy intake and GL but not GI.
Biochemical parameters were similar between groups. There were no significant differences between groups in any of the pregnancy outcomes.
Fewer women in the LGI Group gained an excessive amount of weight (P=0.095)
There was no difference in fetal abdominal circumferences at 36-37 weeks gestation.

Author Conclusion:

In intensely monitored women with GDM, an LGI diet and a conventional HF diet produced similar pregnancy outcomes.

Funding Source:

Government:

Australian National Health and Medical Research Council Project

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)	No
	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.)	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?	No
	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)?	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