DM: Carbohydrates (2007)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
To evaluate the effects of an increase in dietary carbohydrate on blood glucose and lipid metabolism by comparison with a parallel increase of both dietary carbohydrate and fiber.
Inclusion Criteria:
Diabetes mellitus
Exclusion Criteria:
None given
Description of Study Protocol:

Recruitment

Not provided

Design

Comparison of glycemic and lipid indices in 6 subjects with type 1 diabetes and 8 subjects with type 2 diabetes who ate 3 weight maintaining diets (low carbohydrate/low fiber; high carbohydrate/low fiber; high carbohydrate/high fiber) for ten days each in randomized order on a metabolic ward.

Blinding used (if applicable)

 no

Intervention (if applicable)

Patients were admitted to a metabolic ward and given three weight-maintaining diets in a random order and for consecutive periods of 10 days.  Patients were weighed daily, and at the end of each dietary period, blood samples were drawn for glycemic and lipid analyses.

Nutrients Low CHO/low fiber diet High CHO/low fiber diet High CHO/high fiber diet
Carbohydrate (% of energy) 42 53 53
Plant fiber (g) 20 16 54
Protein (% of energy) 21 17 17
Fat (% of energy) 37 30 30

  • Plant fiber sources were leguminous (45%), vegetables (37%), wholemeal bread (12%), fruits (6%).
  • The three diets had similar amounts of soluble carbohydrate and an identical polyunsaturated/saturated fat ratio. "Simple carbohydrates were similar among the diets; however, "complex carbohydrate increased significantly in both of the high carbohydrate diets.
  • Diets were composed of natural food stuffs easily available at any food-shop 

 Statistical Analysis

  • Student's paired t-test (comparisons among diets)
  • Two way analysis of variance  (interaction between diets and type of diabetes)

 

Data Collection Summary:

Timing of Measurements

At the end of each 10 day period

Dependent Variables

  • Fasting blood glucose
  • 2-hr postprandial blood glucose
  • Average daily blood glucose
  • LDL cholesterol
  • HDL cholesterol
  • Total serum triglycerides
  • VLDL triglyceride concentration

Independent Variables

  • Calories, macronutrients, fiber (calculated from Italian tables of food composition, and using the Southgate method for the analysis of dietary fiber (J Sci Food Agric, 1969)

Control Variables

  • Weight
  • Diabetes medications
Description of Actual Data Sample:

Initial N: 14 subjects - 8 type 2 and 6 type 1 diabetic patients

Attrition (final N): 14

Age: type 2: mean 47±5 years; type 1: mean 33±13years

Ethnicity: not provided

Other relevant demographics:

  • Duration of diabetes (type 2): 7±2 yrs
  • Duration of diabetes (type 1): 12±6 yrs

Anthropometrics:

  • Average body mass index (type 2): 28±5 kg/m2
  • Average body mass index (type 1): 22±4 kg/m2

Location:

University of Naples, Naples, Italy

 

Summary of Results:

 

Variables

Low CHO/low fiber diet, n=14

Mean±SD

High CHO/low fiber diet, n=14

Mean±SD

High CHO/high fiber diet, n=14

Mean±SD

Statistical Significance

Fasting blood glucose (mmol/L)

6.9±2.5 6.8±2.0  6.4±2.2

NS

2-hr post-prandial blood glucose (mmol/L)

 8.7±3.9

 9.0±2.9

 6.8±2.7*

 *p<0.01 vs either of the other diets

Average daily blood glucose (mmol/L)

 7.5±1.5

 7.8±2.0

 6.4±2.2*+

*p<0.02 vs high CHO/low fiber diet

+p<0.005 vs low CHO/low fiber diet 

Total serum cholesterol (mmol/L) 5.6±0.9 5.9±1.3 4.7±0.7*+

*p<0.01 vs high CHO/low fiber

+p<0.001 vs low CHO/low fiber

LDL cholesterol (mmol/L) 3.6±0.8 3.8±1.3 2.8±0.7*+

*p<0.01 vs high CHO/low fiber

+p<0.001 vs low CHO/low fiber

HDL cholesterol (mmol/L) 1.5±0.4 1.4±0.4 1.3±0.3* *p<0.005 vs low CHO/low fiber diet
VLDL triglyceride (mmol/L) 0.8±0.3 1.1±0.6 0.9±0.5* *p<0.05 vs high CHO/low fiber diet

 

Other Findings

  • Fasting blood glucose was not significantly influenced by either type of diabetes or type of diet
  • The type of dietary treatment, but not the type of diabetes had a significant influence on the 2-hr postprandial blood glucose concentration
  • No significant differences between the three diets were found for total triglycerides
  • A significant influence of the type of dietary treatment was found for LDL-cholesterol;a significant influence of the type of diabetes was found for VLDL triglycerides.
  • A slight but significant increase in body weight was observed at the end of the high CHO/high fiber diet (64.4±11.6 kg) vs the low CHO/low fiber diet (64.0±11.5 kg), p< 0.02).
  • Diabetes medications for the type 2 subjects were not modified during the study; four out of six type 1 subjects reduced their insulin dosage by an average of 4 units/d during the high CHO/high fiber diet.
Author Conclusion:

A simple increase of digestible carbohydrate without a parallel increase of dietary fiber does not help in improving the metabolic control of diabetic patients.

The hypoglycemic and hypolipidemic effects of high carbohydrate/high fiber diets are due principally to dietary fiber.

Funding Source:
Not-for-profit
1
Reviewer Comments:

This is a metabolic ward study and diets were meticulously designed and adherence guaranteed.  While the diets contained foods commonly available, they may not be realistic in the "real world" particularly the large amount of legumes per day.

It is not clear that a full benefit of a diet such as this can be seen in 10 days, especially for the lipid components.

Medications which might affect glycemic or lipidemic control, other than oral diabetes agents or insulin, were not mentioned/followed

Laboratory analyses methods for specific outcome measures was not described

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? No
  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? ???
  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? ???
  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? ???
  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? 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? ???
  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