DM: Carbohydrates (2007)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
To explore epidemiologic evidence for the relationship between dietary intake and glycemic control.
Inclusion Criteria:
  • Caucasian
  • First visit to Joslin Diabetes Center between Jan 1, 1967 and Dec 31, 1972
  • Type 1 diabetes diagnosed < 2 years before the first visit
  • Under the age of 21 at first visit
  • Resided in Massachusetts on the date of the first visit
Exclusion Criteria:
None given
Description of Study Protocol:

Recruitment : Joslin Diabetes Center

Design

Comparison, by quartiles of HbA1, of dietary intake for previous year (based on a semiquantitative FFQ) and other factors affecting diabetes control.

Blinding used (if applicable)

Not applicable

Intervention (if applicable)

Not applicable

Statistical Analysis

  • Participants were divided into quartiles of HbA1
  • Analysis of variance (multiple comparison tests for mean energy and nutrient intakes and clinical characteristics between the quartile groups)
  • Duncan's multiple-range test (multiple comparison tests for mean energy and nutrient intakes and clinical characteristics between the quartile groups)
  • Spearman correlation coefficients (calculated between energy and nutrient intakes and HbA1 and between clinical characteristics and HbA1
  • Multiple regression analysis (study relationships between intakes of energy and HbA1 and between total fat and HbA1, controlling for covariates - body weight, activity index, insulin dose)
Data Collection Summary:

Timing of Measurements

 One time

Dependent Variables

  • HbA1 (high pressure liquid chromatography)

Independent Variables

  • Usual dietary intake (Willett's semiquantitative food frequency questionnaire - 116 questions covering previous year; daily nutrient intakes calculated primarily according to data from the USDA Handbook No 8 series; sucrose intake from Southgate, J Hum Nutr 1978; fiber intake from McCance and Widdowson's The Composition of Foods, 4th ed).

Control Variables

  • physical activity (interviewer-assisted questionnaire and calculation to determine activity index)
  • insulin dose
  • duration of diabetes
  • age
  • BMI
Description of Actual Data Sample:

Initial N: 162 subjects were asked to fill out the FFQ

Attrition (final N): FFQ information from 136 subjects was used in this analysis (79 men, 57 women)

Age: mean of 28.3 - 30.1 yrs for men; 29.5-30.1 for women

Ethnicity: Caucasian

Other relevant demographics:

  • 80% of subjects were on a twice-a-day insulin schedule; 20% on an once-a-day schedule
  • duration of diabetes: mean of 17.1 - 18.3 yrs for men; 17.4-17.8 yrs for women
  • physical activity index: mean of 30.5 - 39.1 for men; 30.8 - 31.5 for women

Anthropometrics

  • mean BMI: 23.3-25.5 kg/mfor men; 23.8- 25.2 for women

Location: Joslin Diabetes Center, Boston MA

 

Summary of Results:

Findings

  • Individuals were poorly controlled: HbA1 for men was 11.3±1.9, and for women,11.5±2.1.
  • In quartiles of HbA1, dietary fiber was 8.1 to 9.3 g/1000 kcal for men (no significant differences between quartiles) and 10.0-11.4 g/1000 kcal for women (no significant differences between quartiles)
  • In men, absolute intakes of energy, carbohydrate, protein, fat, and dietary fiber were positively correlated with HbA1(p<0.05).  In women the correlations were weaker and not significant.
  • When carbohydrate, protein, fat, and dietary fiber were expressed as a percentage of energy or as an amount per 1,000 kcal, only percentage of energy from fat showed a significant association with HbA1 (men only).
  • Adjustment for body weight, insulin dose, and physical activity using multiple regression analysis did not change the relationship between HbA1 and intakes of energy and fat
  • Sucrose and alcohol intakes did not show any association with HbA1; however the majority of subjects consumed only small amounts of sucrose and alcohol.  

 

Author Conclusion:
  • Among men with type 1 diabetes, the major dietary correlates of poor glycemic control were high intake of energy and percentage of energy from fat.  Further investigation is needed to confirm this relationship
  • An absolute intake of fiber (reflecting energy intake) was associated with poor glycemic control.  When fiber was expressed per 1,000 kcal, there was no association with glycemic control, which suggests that the fiber composition of diet has no effect on long-term glycemic control in patients with type 1 diabetes.
Funding Source:
Government: NIH
Reviewer Comments:

This study presents a random sampling of a very specific group of subjects with type 1 diabetes, and thus the results cannot be extrapolated to other populations.  And, because this is a cross-sectional study, it does not prove a cause and effect relationship between nutrients and HbA1.

A strength of this study is that authors were able to control for covariates in their analyses:

  • The type of statistics for this study are take into consideration a number of confounding variables which can affect blood glucose control (weight, physical activity, insulin dose)
  • the HbA1 quartiles were presented by gender

The Harvard semiquantitative food frequency questionnaire is a reliable and validated product.  While the resources used to do the nutrient calculations were valid for the time, using a UK database for the fiber calculations may not have the same validity in US foods 

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) N/A
  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) N/A
 
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? 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? No
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? N/A
  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? ???
  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? ???
  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? N/A
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? N/A
  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? N/A
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? N/A
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? N/A
  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? 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? N/A
  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