EAL

GDM: Macronutrients (2008)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

To test the hypothesis that a woman's dietary carbohydrate mix modifies the glucose and insulin response to both mixed caloric intake and exercise.

Inclusion Criteria:

None specifically mentioned.

Exclusion Criteria:

None specifically mentioned.

Description of Study Protocol:

Recruitment: methods not specified

Design: Randomized Crossover Trial, Longitudinal Study

Blinding Used (if applicable): not applicable

Intervention (if applicable):

Protocol 1:

14 physically active nonpregnant women maintained a standard exercise program

Protocol 2:

12 women who completed an uncomplicated pregnancy were enrolled before conception.

Placed on a regular exercise regimen of supervised exercise (20 minutes, weight bearing, 3 x/wk at an intensity of 55% of each individual’s VO₂max). All followed the low glycemic index diet until 8 wks gesation when they were randomly assigned to either the low glycemic or high glycemic diet for the remainder of the study.

Diet for both protocols:

Total kcal based on fat-free mass estimated from sum of 5 site skinfold thicknesses and weight stability in the nonpregnant state (35-45 kcal/kg lean body mass/d). Pregnant women allowed to increase kcal to appetite with advancing gestation.
Diet composition: 17-19% protein, 20-25% fat, 55-60% carbohydrates.
Dietary compliance assessed by 24-h recall conducted randomly 2x/wk throughout the study.
Test meals: 540 kcal, 17% protein, 55% carbohydrate, 28% fat, 2.5-3.5 g fiber. Glycemic index (low: 54, high 92) Low glycemic diet consisted of all-Bran cereal, grapefruit, whole grain bread, peanuts, apples, oranges, peas, fettucini. High glycemic diet consisted of Rice Chex cereal, banana/mango, Kaiser roll, corn or potato chips, baked potato, carrots, angel food cake, graham crackers, candy bar, soda

Statistical Analysis

Significant differences in the areas under or above the glucose and insulin response curves were detected using either the paired t test in the first protocol or repeated measures ANOVA and the unpaired t test between groups in the second protocol.

Data Collection Summary:

Timing of Measurements

Indwelling venous catheter placed for collecting baseline, 30, 60, 90, 120 and 180 minute postprandial blood for glucose and insulin.
20 minutes of treadmill at 55% of VO_2max confirmed by indirect calorimetry over the last 10 minutes of exercise followed by 1 hour of rest. Blood samples taken during 10 and 20 minutes of exercise and at 15, 30 and 60 minutes after exercise.

Dependent Variables:

Whole blood glucose
Serum insulin

Independent Variables:

Protocol 1 vs Protocol 2
Diet

Control Variables

Description of Actual Data Sample:

Initial N: 14 control women: healthy, active, and from middle or upper socioeconomic class with 14 to 30% body fat and VO_2max between 30 and 52 ml/kg/min.

Attrition (final N): 14

Age: range 26 - 37 years

Ethnicity: not mentioned

Other relevant demographics:

Anthropometrics No significant differences between groups

Location: not specified

Summary of Results:

Other Findings

Protocol 1

The average increase in blood glucose values was significantly higher after eating the low glycemic index compared to the high glycemic index diet (6.3+0.6 vs. 13.5+0.9 mg/min, P<0/001).

The average insulin responses were similar in direction (17+1 vs. 28+2 mU/min, P<0.001).

The glycemic response to exercise was significantly lower on the high glycemic diet (-0.7+0.4 mg/min vs. –4.4+0.5 mg/min, P<0.01).

The response of insulin to exercise was greater in the high glycemic diet (-8.0+5.3 mU/ml vs. –3.9+1.4 mU/ml., P<0.05)

Protocol 2:

Those on the high glycemic diet had increases in the area under the glucose curve with advancing gestation that plateaued in mid and late gestation by mid/late gestation to 75% above prepregnancy levels (P<0.001) whereas there was no significant change in women on the low glycemic diet.

The area under the insulin response curve was higher in those on the high glycemic diet (P<0.05-0.01) and was higher for women on both diets in late pregnancy (P<0.01).

Author Conclusion:

These findings support earlier work suggesting that the combination of exercise and diet may improve glycemic control in gestational diabetes to a greater extent than diet alone.

The type of dietary carbohydrate in a healthy, physically active woman’s diet influences both her postprandial blood glucose profile and her blood sugar responses to exercise in both the pregnant and nonpregnant state.

Funding Source:

Government:	NIH
University/Hospital:	MetroHealth Medical Center

Reviewer Comments:

Well-designed study.

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?	No
	2.2.	Were criteria applied equally to all study groups?	N/A
	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?	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?	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?		Yes
	10.1.	Were sources of funding and investigators' affiliations described?	Yes
	10.2.	Was the study free from apparent conflict of interest?	Yes