DM: Carbohydrates (2007)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
To compare metabolic effects of a high-carbohydrate, high-fiber (HCHF) diet and a low-carbohydrate, low-fiber (LCLF) diet in subjects with type 1 diabetes in a metabolic ward setting.
Inclusion Criteria:
Insulin dependent diabetes mellitus
Exclusion Criteria:

History of clinically significant renal, hepatic, or neurologic disease

Description of Study Protocol:

Recruitment

Not provided. 

Design

Comparison, by diet (HCHF or LCLF), of insulin requirements, and glycemic and lipid control, measured 4 weeks after each diet.

Blinding used (if applicable)

None.

Intervention (if applicable)

All subjects, hospitalized on a metabolic ward, received the LCLF diet for 1 week and then were randomized to either the LCLF or the HCHF diet for 4 weeks. After a 4-6 week washout period when subjects followed their usual diets, they were readmitted to the metabolic ward for 4 weeks on the alternative diet.  At the end of each hospitalization subjects underwent a 24 hour period on the artificial pancreas (Biostator).  Both diets were weight-maintaining, consisted of commonly available foods, and were given in a 2-day rotation:

  • LCLF - 39% of energy as carbohydrate (50% simple, 50% complex), 20% protein, 41% fat, 500 mg cholesterol, and 5 g dietary fiber/1000 kcal.  Diet consisted of high-fat, low-fiber foods plus moderate amounts of meats and dairy products.
  • HCHF - 70% of energy as carbohydrate (25% simple, 75% complex), 20% protein, 10% fat, 50 mg cholesterol, and 35 g dietary fiber/1000 kcal.  Diet consisted of high-fiber foods such as whole-grain/bran cereals, dried beans, vegetables and fruits plus small quantities of meats and dairy products.

Insulin: While on the metabolic ward, all subjects received a combination of NPH and Regular insulin before breakfast and before the evening meal, and some subjects received Ultralente at 10 PM, with the treatment goal being maintenance of optimal glucose control.  Small changes were made when necessary to prevent symptomatic hypoglycemia and persistent hyperglycemia.

Statistical Analysis

  • Analysis of variance for a two-period crossover design (effects of diets on all indices)
  • Least squares estimates (for difference between diet means, adjusted for each subject and period effects)
Data Collection Summary:

Timing of Measurements

Daily (FPG, 24-hr urine glucose excretion); twice weekly (lipids); weekly (glycosylated hemoglobin); 4 weeks after the start of each diet (insulin requirements)

 Dependent Variables

  • Fasting plasma glucose
  • 24-hr urine glucose excretion
  • Glycosylated hemoglobin (Bio-Rad Hemoglobin A1cMicro Column Test method
  • Total cholesterol (cholesterol esterase and cholesterol oxidase assay)
  • Serum triglyceride (hydrolyzing the triglycerides and measuring the released glycerol
  • Serum HDL-cholesterol (same method as total cholesterol after removing LDL-cholesterol and VLDL-cholesterol)
  • LDL-cholesterol (calculated from total cholesterol, HDL-c and triglyceride concentrations
  • Urine C peptide (double-antibody radioimmunoassay kit)
  • 20 hr, basal, and meal-related insulin requirements (calculated from Biostator data)

Independent Variables

  • Fiber, energy and macronutrients (calculated using a computer database described in Diabetes Care 1978;293-302)
  • Weight 
  • Insulin doses

 Control Variables

  • Drugs known to affect glycemic control

 

Description of Actual Data Sample:

Initial N: 12 (10 men, 2 women)

Attrition (final N): 10 (9 men, 1 woman)

Age: Range from 35-65 yrs

Ethnicity: not provided

Other relevant demographics: Duration of diabetes - 1-40 yrs (mean 18.3 yrs)

Anthropometrics: Mean BMI - 23.3 ±2.43 kg/m2

Location: VA Medical Center and University Kentucky College of Medicine, Lexington, KY

 

Summary of Results:

 

Variables

LCLF (4 wk measure)

mean±SE

HCHF (4 wk measure)

mean±SE

Statistical Significance of Group Difference

Glycosylated hemoglobin (%), n=8

8.13±0.37 8.01±0.33

NS

Total cholesterol (% from baseline), n=10

 -14.3±3.5

-26.3±3.8

 P<0.001 (HCHF from LCLF after adjustment for subject and period effects)

LDL-cholesterol (% from baseline), n=10

-6.5±9.2 

-28.8±3.5

 NS

HDL-cholesterol (% from baseline), n=10 -8.3±3.7 -29.3±3.6 P<0.001 (HCHF from LCLF after adjustment for subject and period effects)
Triglycerides (% from baseline), n=10 -26,3±9.5 -9.8±6.4 NS

Other Findings

  • Average body weight did not differ significantly on the two test diets.
  • Glycemic control  (FPG, 24-hr urine glucose excretion) was identical on both diets
  • As designed, total carbohydrate intake was 1.6 times greater on the HCHF diet than on the LCLF diet; total fiber intake increased from 5 to 34 g/1000 kcal on the HCHF diet while the soluble fiber intake increased by > 20 g/d.
  • Glycemic control during the Biostater did not differ significantly between the two diets.
  • Basal insulin requirements were estimated to be 3.78 U (p<0.025) lower on the HCHF diet than on the LCLF diet.
  • 24-h and meal related insulin requirements did not change significantly, and no effects of diet period or sequence were observed.
  • During the study 3 subjects received drugs known to affect glycemic control (nitrates and a calcium channel blocker for angina in 2 subjects throughout the study; clonidine (5 wks) and then enalapril for the duration of the study to treat hypertension in 1 subject).
Author Conclusion:

HCF diets providing 70% of energy as carbohydrate and  70g dietary fiber/d significantly decrease basal insulin requirements and increase peripheral glucose disposal in individuals with type 1 diabetes without altering glycemic control

Diets, as above, also significantly decrease serum total cholesterol without affecting serum triglycerides or LDL-HDL cholestero ratios.

Funding Source:
Government: NIH
Not-for-profit
0
Foundation associated with industry:
Reviewer Comments:
  • This study is a meticulously detailed and conducted nutrition study, with a metabolic unit used to provide investigator control of subjects.  Because of the close control, this study does not reflect a free-living ability to increase fiber in the diet.
  • In this study macronutrient % of calories was varied as well as the fiber; consequently the results of this study are not specifically fiber related.
  • Four weeks is a not long enough time to see a difference in glycoslyated hemoglobin measures
  • Since optimal glycemic control was not achieved in most subjects, these results may not be fully applicable to subjects with good to excellent control

 

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? ???
  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? ???
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? 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? ???
  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? 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? 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? ???
  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