GDM: Carbohydrate (2016)

Cypryk K, Kaminska P, Kosinski M, Pertynska-Marczewska M, Lewinski A. A comparison of the effectiveness, tolerability and safety of high and low carbohydrate diets in women with gestational diabetes. Polish Journal of Endocrinology, 2007; 58: 314-319. PubMed ID: 18058723
Study Design:
Randomized Controlled Trial
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Quality Rating:
Neutral NEUTRAL: See Quality Criteria Checklist below.
Research Purpose:
To evaluate the effectiveness and safety of high and low carbohydrates diets by their impact on glucose blood concentration and ketone production in women with gestational diabetes mellitus (GDM).
Inclusion Criteria:
  • Treated at the Outpatient Clinic of Diabetes and Metabolic Diseases at the Research Institute of the Hospital of the Polish Mother
  • Pregnant women
  • Diagnosis of GDM diagnosed according to WHO criteria
  • Written consent.
Exclusion Criteria:
No diagnosis of GDM diagnosed according to WHO criteria.
Description of Study Protocol:

Recruited from clinic at the Outpatient Clinic of Diabetes and Metabolic Diseases at the Research Institute of the Hospital of the Polish Mother.


  • A total of 30 pregnant women were randomized into two groups: Those on a low-carbohydrate diet in which the daily supply of energy derived for carbohydrates was 45% of energy intake (Group A) and those on a high-carbohydrate diet in which the daily contribution of carbohydrates was over 60% of energy intake (Group B)
  • Before diet intervention, glycemia levels were obtained from the patients' diaries during the previous three to four days so that average 24-hour glycemia under normal diet conditions could be estimated
  • All patients were educated by qualified dietitian with regard to diet components and meal preparation methods
  • Intervention diet was followed for 14 days. During this time, home glucose monitoring was performed and recorded by the patient four times a day (fasting and two hours after each main meal)
  • Presence of urine ketones was checked by the patient daily using test strips
  • Body mass was measured
  • At conclusion of diet intervention, diaries were analyzed and compliance with nutritional recommendations was estimated
  • Patients were asked to continue the diet until delivery and obstetric results were evaluated
  • During pregnancy, goal blood glucose values are fasting of no more than 90mg per dL and two hours after meals of no more than 120mg per dL.

Intervention Diets

  • Group A diet intervention: 45% energy from carbohydrates, 25% energy from protein and 30% energy from fat
  • Group B diet intervention: 60% energy from carbohydrates, 25% energy from protein and 15% energy from fat.

Blinding Used

Low- or high-carbohydrate diet.

Statistical Analysis

  • Student's T-test for the comparison of glycemia levels between Groups A and B before and after the treatment
  • Mann-Whitney test used where there was infringement of the normality presumption and divergence equality in groups
  • Parametric T-tests applied for dependent trials
  • P value of less than 0.05 was considered statistically significant.
Data Collection Summary:

Timing of Measurements

  • Glycemia levels measured via patient recorded diaries for three or four days before start of intervention
  • Home blood glucose monitoring conducted four times per day; fasting and two hours after each main meal
  • Urine ketones checked by patients every day during 14-day diet period
  • Body mass measured
  • Patient diet diaries recorded daily and analyzed on Day 15 to assess compliance with nutrition recommendations
  • Obstetric results evaluated after delivery.

Dependent Variables

  • Blood glucose levels
  • Obstetric results
  • Urine ketones.

Independent Variables

Carbohydrate content of diet.

Control Variables

  • Age
  • Pregnancy duration
  • Diet compliance
  • Body mass.
Description of Actual Data Sample:
  • Initial N: 30 females
  • Attrition (final N): 30 females
  • Age: Mean 28.7 years; minimum 21 years and maximum 38 years, SD=3.7
  • Ethnicity: Not described
  • Other relevant demographics: None
  • Anthropometrics: Average values for glycemia did not significantly vary between the two groups before the diet treatment 
  • Location: Lodz, Poland.
Summary of Results:

Key Findings

  • In the low-carbohydrate diet group (Group A), no changes in fasting blood glucose were noted during the period studied, but a significant decrease in average post-prandial glucose concentrations was observed
  • In the high-carbohydrate diet group (Group B), fasting and after-breakfast glucose concentrations did not change after implementation of the diet, but a significant decrease in glycemia levels was noted after lunch and dinner
  • Ketonuria was not observed in either group
  • Diets appeared to be insufficiently effective in three patients; two patients from Group A and one patient from Group B required insulin therapy
  • No significant differences observed in obstetric outcomes between groups.
  Group A (low-carbohydrate diet) Group B (high-carbohydrate diet)
Blood glucose concentration (mg/dl) P-value Blood glucose concentration (mg/dl) P-value

Time of Glycemia Measurements

Before diet implementation

After diet implementation

Before diet implementation After diet implementation





77±8 76±7 0.307

After Breakfast




94±12 89±7 0.189

After Lunch




106±15 96±7 0.012
After Dinner 112±16 103±13 0.011 107±12 97±7 0.003


Diabetic Results Group A Group B P-Value

Gestational Age at Delivery (weeks)




Mode of Delivery: Physiological




Mode of Delivery: Caesarean Section




Mode of Delivery: Other




Mean Birth Weight (grams) 3407±309 3385±418 >0.05
Birth Weight >4,000g 0 0 >0.05
Apgar Scale 9.6±0.6 9.1±0.9 >0.05

Other Findings

  • Proper weight change was observed in all patients studied
  • 12 patients from Group A and 11 patients from Group B fully applied the recommended menu
  • Three patients in Group A and four patients in Group B claimed that they did not fully apply the menu.
Author Conclusion:
  • Study findings prove the effectiveness and safety of both low- and high-carbohydrate diets. Both high- and low-carbohydrate diets are safe, as no trace of acetone was observed in urine samples and the comparable obstetric results.
  • A diet with carbohydrate limitations should be recommended to women who experience the highest glycemia levels after breakfast
  • Further research regarding evaluation of the effect of carbohydrate supply on the 24-hour glycemic level in the diets of women with GDM should be completed.
Funding Source:
University/Hospital: Medical University of Lodz
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? ???
  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? ???
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? No
  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.) 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? ???
  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? 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? ???
  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)? ???
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? ???
  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