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GDM: Macronutrients (2008)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
To evaluate the effect of percentage of carbohydrates on glucose response to breakfast, lunch, and dinner in subjects with gestational diabetes mellitus.
Inclusion Criteria:

None specifically mentioned.

Exclusion Criteria:
None specifically mentioned.
Description of Study Protocol:

Recruitment:  14 untrained gestational diabetic women diagnosed according to standard protocol were recruited between 32 and 36 weeks gestation.

Design:  Cohort Study

Blinding Used (if applicable):  Not applicable

Intervention (if applicable):

  • Each woman was instructed to perform blood glucose self-monitoring 4 times/d (before breakfast, and 1 h after each meal).
  • Each subject was placed on a diet of 24 kcal/kg/24 h with distribution of kcal as follows:  Breakfast:  12.5%, Lunch:  28%, Dinner:  28%
  • The remainder of the kcal divided among 3 snacks.
  • Each week, all subjects were seen by a physician, and food records were collected and analyzed for % of carbohydrate at each meal.
  • Insulin was initiated if fasting plasma glucose was >5.83 mmol (105 mg/dl) or 1 h postprandial plasma glucose remained >7.78 mmol (140 mg/dl)

Statistical Analysis

Statistical analysis was based on simple linear regression.  Meal contents were highly consistent, and therefore mean values of 10 measurements after a meal of a specific percentage of carbohydrates were evaluated for each individual.

Data Collection Summary:

Timing of Measurements:

Blood glucose self-monitoring 4 times/d, between 32 and 36 weeks gestation.

Dependent Variables

  • Postprandial blood glucose

Independent Variables

  • Each woman was instructed to perform blood glucose self-monitoring 4 times/d (before breakfast, and 1 h after each meal).
  • Each subject was placed on a diet of 24 kcal/kg/24 h with distribution of kcal as follows:  Breakfast:  12.5%, Lunch:  28%, Dinner:  28%
  • The remainder of the kcal divided among 3 snacks.
  • Each week, all subjects were seen by a physician, and food records were collected and analyzed for % of carbohydrate at each meal.
  • Insulin was initiated if fasting plasma glucose was >5.83 mmol (105 mg/dl) or 1 h postprandial plasma glucose remained >7.78 mmol (140 mg/dl)

Control Variables

Description of Actual Data Sample:

Initial N:  14 untrained gestational diabetic women

Attrition (final N):  14

Age:  Mean age: 30.9 + 2.8 yr

Ethnicity:  not mentioned

Other relevant demographics:  All women were >130% of IBW, Mean weight: 75.6 + 7.8 kg, Fasting C-peptide:1.87 to 3.0 pmol, Mean initial HgA1c: 4.89 + 0.40%

Anthropometrics:

Location:  California

Summary of Results:

Other Findings

10 postprandial values for each meal were averaged for each of the 14 women (total of  140 measurements per meal). 

The correlation between % of carbohydrates and postprandial glucose level at 1 hour was strongest for dinner (r=0.95, P<0.001) with more variability seen at breakfast (r=0.75, P=0.002) and lunch r=0.86, P=0.001). 

Based on the results of statistical analysis, to maintain a 1 h postprandial whole blood glucose level < 7.78 mmol (138 mg/dl) the following % of carbohydrates needed would be:  45% breakfast, 55% lunch, 50% dinner. 

To maintain a 1 h postprandial whole blood glucose level <6.67 mmol (104 mg/dl) the % of carbohydrate needed would be:  33%, 45% and 40% for breakfast, lunch and dinner, respectively.

Author Conclusion:

The glycemic response to a mixed meal in subjects with gestational diabetes is highly correlated with the percentage of carbohydrates.  Of the ingested meal and varies among individuals and among breakfast, lunch and dinner. Therefore, the amount of carbohydrate appropriate to maintain glycemic control needs to be individualized based on SBGM.

Funding Source:
University/Hospital: Sansum Medical Research Center
Reviewer Comments:

It was not reported if a dietitian instructed the subjects on the diabetic diet.

Many details about the study and the results are lacking in this paper. For example, the average blood glucose values at each meal. 

Treatment goals for GDM are a 1-hr postprandial <7.78 mmol/L (140 mg/dl) therefore the distribution of carbohydrates to meet this goal would be:  45% breakfast, 55% lunch, 50% dinner or an average of 50% carbohydrate in the day’s diet.

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? No
  2.2. Were criteria applied equally to all study groups? ???
  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? N/A
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) N/A
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? N/A
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) N/A
  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? N/A
  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? Yes
  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? N/A
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? ???
  9.1. Is there a discussion of findings? Yes
  9.2. Are biases and study limitations identified and discussed? No
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