GDM: Carbohydrate (2016)

Hernandez TL, Van Pelt RE, Anderson MA, Daniels LJ, West NA, Donahoo WT, Friedman JE, Barbour LA. A higher-complex carbohydrate diet in gestational diabetes achieves glucose targets and lowers postprandial lipids: a randomized crossover study. Diabetes Care, 2014 DOI: 10.2337/dc13-2411. PubMed ID: 24595632
Study Design:
Randomized Crossover Trial
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Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:
To determine in women with gestational diabetes mellitus (GDM) whether a diet that liberalized total carbohydrate [higher-complex, lower-glycemic index (GI) foods] and minimized fat could effectively control maternal glycemia and post-prandial lipids.
Inclusion Criteria:
  • Diagnosis of GDM at 24-28 weeks gestation
  • On diet alone
  • 20 years to 36 years of age
  • BMI 26kg/m2 to 39kg/m2
  • English speaking.
Exclusion Criteria:
  • Multiple gestation
  • Fasting triglycerides (TG) over 400mg per dL
  • Suspected overt diabetes (hbA1c  at least 6.5)
  • Smoker
  • Likely to fail diet (fasting glucose over 110mg per dL)
  • Risk factors for placental insufficiency and growth restriction or preterm delivery or with major medical disorders.
Description of Study Protocol:
  • Recruitment: University Hospital and Kaiser Permanente Colorado
  • Design: Randomized crossover
  • Blinding used: Women were blinded to CGMS glucose concentrations
  • Intervention: Three days of a conventional lower carbohydrate (LC) and high fat (CONV) diet with randomized crossover to a higher-complex carbohydrate (HCC) lower fat (LF) Choosing Healthy Options in Carbohydrate Energy (CHOICE). Each was separated by a washout/control diet for two days
  • Statistical analysis: Shapiro-Wilk test for normality of outcome variables. Paired T-tests on halved crossover differences between sequences were used to assess the period effects.
Data Collection Summary:

Timing of Measurements

  • 10-hour venous blood sample on Day One
  • Continuous glucose monitoring system (CGMS) on Days Three through Five
  • Day Six: Fasting baseline blood and after a standard breakfast, hourly bloods for five hours
  • Days Three through Six were repeated on Days Nine through 12.

Dependent Variables

  • Plasma glucose, insulin, TG, fatty fat acid (FFA)
  • Lipids and LDL-C
  • HbA1c
  • Insulin resistance
  • C-peptide
  • Interstitial glucose by CGMS.

Independent Variables

  • LC/CONV diet: 40% CHO, 45% fat, 15% protein
  • HCC/LF (CHOICE) diet: 60% CHO, 25% fat, 15% protein, enriched in complex CHO (polysaccharides and starches primarily from grains, vegetables and fruits that tend to attenuate a sharp post-prandial rise in plasma glucose). 

Control Variables

  • Standardized breakfast after each diet: 30% of total daily energy intake and slightly higher than the 25% of daily energy consumed, while wearing the CGMS and matched to the macronutrient content of the previous 72 hours
  • Calorie intake of both diets was 24kcal per kg of overweight women and 18kcal per kg for obese women
  • Initial two days and between-random assignment washout/control diet was 50% CHO, 35% fat, 15% protein.
Description of Actual Data Sample:
  • Initial N: 19 females
  • Attrition (final N): 16
  • Age: 28.4±1.0 years
  • Ethnicity: Five Hispanic, one Asian, one African-American, nine Caucasian.
Other Relevant Demographics
  • Anthropometrics: BMI, 33.6±1.1kg/m2
  • Location: Colorado.
Summary of Results:
  • No between-diet differences within the women for fasting or pre-prandial glucose
  • When meals were considered together as a mean across three meals, both one- and two-hour post-prandial glucose were modestly higher on the CHOICE diet (one hour, HCC/LF 115±2mg vs. LC/CONV 107±3mg per dL, P ≤0.01;  two-hour, HCC/LF 106±3mg vs. LC/CONV 97±3mg per dL, P≤0.001)
  • The two-hour post-prandial glucose AUC across meals was modestly higher on CHOICE  vs. LC/CONV diet (HCC/LF 12,780±337mg vs. 12,086±325mg per minute per dL; P≤0.009
  • There was no significant difference in time to postprandial glucose peak between diets
  • Mean glucose measures and total AUC derived from CGMS were not different between diets within the women on mean nocturnal and 24-hour glucose
    • The daytime mean glucose was slightly higher on CHOICE compared with LC/CONV (P=0.03)
    • The daytime glucose AUC was higher on CHOICE vs. LC/CONV (P=0.01), as was the 24-hour glucose AUC (P=0.02)
    • Despite these differences, the patterns of glycemia were similar and were well within current treatments targets for daytime, nocturnal, post-prandial and mean glycemia.
Author Conclusion:
Liberalizing complex carbohydrates and reducing fat still achieved glycemia below current treatment targets and lower post-prandial FFAs. 
Funding Source:
Government: NIH, Colorado Program for Nutrition and Healthy Development
University/Hospital: University of Colorado Diabetes and Endocrinology Research Center
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.) 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? N/A
  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? N/A
  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)? N/A
  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