GDM: Macronutrients (2008)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:

To determine whether higher dietary fiber intake (water soluble and insoluble) is associated with lower insulin requirements and better glycemic control in pregnant women with type 1 diabetes consuming a self-selected diet.

Inclusion Criteria:
  • Diagnosis of type 1 diabetes mellitus based on history of ketoacidosis or C-peptide levels
  • Singleton pregnancy
  • Provided at least 1, 3-day food record
Exclusion Criteria:

None specifically mentioned.

Description of Study Protocol:

Recruitment

The Diabetes in Pregnancy Program:  231 women with type 1 diabetes mellitus were followed to study the effect of glycemic control on the outcome of pregnancy.  Women were enrolled between November 1983 and February 1991.

Design:  Cohort Study

Blinding Used (if applicable):  not applicable

Intervention (if applicable):

1. Intensive management:

  • multiple insulin injections, mixture of short and intermediate acting
  • clinic visits q 1-2 wk throughout pregnancy
  • monthly HbA1c, 42 days after food records collected

2.  Self-monitoring of blood glucose 3 times/d

  • pre-meals
  • precision of glucose meter checked
  • target ranges: mmol/L
  • pre-meal: <5.55 (100 mg/dl)
  • 90 minute postprandial: <6.66  (120 mg/dl)
  • Insulin records collected during clinic visits within 7 days before or after food records were collected

3.  Nutrition counseling

  • RD saw patients at each clinic visit (q 1-2 wk throughout the study)
  • Meal pattern: 3 meals, 3 snacks, whole grain breads and cereals
  • Individualized meal plans to achieve blood glucose goals
  • Instructed patients to complete 3-d (2 week day and 1 weekend day) each trimester to assist in nutrition counseling.

4.  Diet analysis using Nutrition Data System, U MN.

Statistical Analysis

Correlation coefficients were calculated to assess the bivariate association between fiber intake and the outcome measures.  Analyses were conducted for each trimester, simple linear regression and calculation of correlation coefficients were used to further evaluate the relationships of interest.  Multiple regression analyses were conducted to statistically control for other factors that might potentially alter the assessment of the associations between fiber intake and insulin requirements and indexes of glycemic control.

Data Collection Summary:

Timing of Measurements

Clinic visits every 1-2 weeks throughout pregnancy.

Dependent Variables:

  • Daily insulin dosage
  • Pre-meal blood glucose
  • HbA1c

Independent Variables:

1. Intensive management:

  • multiple insulin injections, mixture of short and intermediate acting
  • clinic visits q 1-2 wk throughout pregnancy
  • monthly HbA1c, 42 days after food records collected

2.  Self-monitoring of blood glucose 3 times/d

  • pre-meals
  • precision of glucose meter checked
  • target ranges: mmol/L
  • pre-meal: <5.55 (100 mg/dl)
  • 90 minute postprandial: <6.66  (120 mg/dl)
  • Insulin records collected during clinic visits within 7 days before or after food records were collected

3.  Nutrition counseling

  • RD saw patients at each clinic visit (q 1-2 wk throughout the study)
  • Meal pattern: 3 meals, 3 snacks, whole grain breads and cereals
  • Individualized meal plans to achieve blood glucose goals
  • Instructed patients to complete 3-d (2 week day and 1 weekend day) each trimester to assist in nutrition counseling.

4.  Diet analysis using Nutrition Data System, U MN.

Control Variables

Description of Actual Data Sample:

Initial N:  231 were enrolled in the project

Attrition (final N):  141 women met study criteria

Age:  mean age 26.1 +/- 5.4 years

Ethnicity:  not mentioned

Other relevant demographics:

means + SD

gestational age at enrollment:

9.1+5.3 wk (3.4 - 29.4)

age, y

26.1+5.4

prepregnancy BMI

23.2+3.7

Duration of Diabetes, y

13.5+6.9

Anthropometrics:

Location:  United States

Summary of Results:

 

Complications at enrollment (%)
Hypertension 48.9

Renal disease    

20.5

Eye disease    

12.8

Thyroid meds 

 9.0

 

Average nutrient intakes by trimester
  First Second  Third
Kcal  1,914 1,940 1,816
Protein, g 86  87 82

Fat, g

 82 85  80
(%) 38 39  40
Carbohydrate,g 212 211 195
(%) 44 44 43
Dietary fiber, g 14.5 14.3 13.1
Water soluble,g 4.9  5.0   4.5
Insoluble, g 9.5  9.0 8.4

Insulin reguirements/glycemic control

Insulin

First  Second  Third  P

Units/kg Body wt

0.87 0.83   1.02  0.001

Blood glucose (mmol/L) (pre-meal)

6.8 6.4    6.3 NS
HbA1c,% 8.6 7.4  7.4 0.001

Other Findings

In the second and third trimesters of pregnancy, insulin requirements were inversely associated with total, water soluble, and insoluble fiber intakes; correlation coefficients ranged from -0.22 to –0.17 (P=0.02 to 0.08).

Insulin requirements associated with a higher fiber intake (20.5 g/d) were 16% to 18% lower than for a lower fiber intake (8.1 g/d).  These relationships remained after adjustment for body weight, disease severity and duration, insulin type, and study year in the second (P=0.03 to 0.10) but not in the third trimester. 

Pre-meal blood glucose and HbA1c were not associated with fiber intake.

Author Conclusion:

A reduction in insulin requirements due to higher fiber intake has important implications for blood glucose management for individuals with type 1 diabetes mellitus. Insulin dependent individuals may be counseled to increase their dietary fiber intake to reduce serum lipids and heart disease as well as to achieve the other benefits of diets rich in fiber.

If moderate increases in dietary fiber reduce insulin requirements then health care providers should counsel patients to make adjustments in insulin to avoid the possible complications of hypoglycemia, increase in food intake and excess weight gain.

Funding Source:
University/Hospital: Children's Hospital Medical Center, University of Alberta, University of Cincinnati, Northkey Community Care
Reviewer Comments:

This study is consistent with other studies that show that higher fiber diets decrease insulin resistance. In individuals with type 1 diabetes mellitus in this study, higher fiber diets reduced insulin requirements.

The composition of the diets were 44% carbohydrate and 38 to 40% fat and 14 grams fiber.

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? 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? 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? 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? 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