DM: Carbohydrates (2007)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
To determine, in patients with type 2 diabetes, the effects of reducing the blood glucose raising potential of the diet without changing macronutrient composition, on blood glucose and lipid control and urinary C-peptide and urea excretion, respectively, as markers of insulin secretion and colonic fermentation.
Inclusion Criteria:
None specifically mentioned.
Exclusion Criteria:
None specifically mentioned.
Description of Study Protocol:

Recruitment

Recruitment methods not described.

Design

Randomized Crossover Trial.

Blinding used (if applicable)

Not used.

Intervention (if applicable)

Patients were given pre-weighed diets (59% of energy from carbohydrate, 21% fat, and 24 g/1000 kcal dietary fiber) for two 2-week periods, with a diet glycemic index of 60 during 1 period and 87 during the other, separated by 2-week washout.

Statistical Analysis

Statistical analysis was by ANOVA.  The effects of treatment, diet (weight reducing and weight maintaining) and order were assessed by general linear model procedure.  There was no significant effect of order or significant interaction between effects of treatment and diet, indicating no differences between weight-reducing and weight-maintaining diets, thereofre the data for all patients were pooled for statistical analysis.

Data Collection Summary:

Timing of Measurements

Patients were seen weekly for measurements.

Dependent Variables

  • Weight measured to nearest 0.1 kg without shoes
  • Fasting blood samples (venous and capillary) analyzed for glucose, total cholesterol, triglyceride, creatinine, and urea
  • 24-hour urine collections analyzed for C-peptide, creatinine and urea 

Independent Variables

  • Pre-weighed diets (59% of energy from carbohydrate, 21% fat, and 24 g/1000 kcal dietary fiber) for two 2-week periods, with a diet glycemic index of 60 during 1 period and 87 during the other
  • Overweight/obese patients given weight-reducing diets
  • Subjects were given all foods

Control Variables

 

Description of Actual Data Sample:

Initial N: 15 subjects with type 2 diabetes, 7 men, 8 women

Attrition (final N):   15

Age:  mean age 67 +/- 2 years

Ethnicity:  not mentioned

Other relevant demographics:

Anthropometrics:

Location:  Canada

 

Summary of Results:

Other Findings

On the low GI diet, the blood glucose response after a representative breakfast was 29% less than on the high GI diet (874 +/- 108 vs 1204 +/- 112 mmol min/l, P < 0.001), the percentage reduction being almost identical to the 28% difference predicted from the meal GI values.

Fasting blood glucose fell significantly over both dietary periods, but there was no significant difference between the effects of the high and low glycemic index diets.

After the 2-week low GI diet, fasting serum fructosamine and cholesterol levels were significantly less than after the high GI diet (3.17 +/- 0.12 vs 3.28 +/- 0.16 mmol/l, p < 0.05, and 5.5 +/- 0.4 vs 5.9 +/- 0.5 mmol/l, p < 0.02, respectively).

Serum urea and creatinine were not affected by the dietary treatments, and there was no difference in urine volume or creatinine excretion.

Urinary C-peptide excretion, as an index of insulin secretion, was 30% lower on the low than the high GI diet (2.05 +/- 0.30 vs 2.93 +/- 0.49 nmol/mmol creatinine, p < 0.02), urinary urea was reduced by 19% (347 +/- 27 vs 402 +/- 39 mmol/42 hours, p < 0.025), consistent with enhanced colonic fermentation. 

Author Conclusion:
We conclude that low glycemic index starchy foods may be beneficial in the treatment of type 2 diabetes, resulting in reduced postprandial blood glucose responses and improved overall blood glucose and lipid control in the face of reduced urinary C-peptide output, as a marker of insulin secretion, and reduced urinary urea as a marker of increased colonic fermentation.  These results are consistent with the hypothesis that low glycemic index  starchy foods provide another method, in addition to soluble fiber, glucosidase inhibitors, and increased meal frequency, to reduce the rate of carbohydrate absorption.
Funding Source:
Not-for-profit
0
Foundation associated with industry:
Reviewer Comments:
Recruitment methods and inclusion/exclusion criteria not described.  Foods provided.  Small sample size.
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? No
  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? 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? N/A
  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)? N/A
  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