EAL

DM: Carbohydrates (2007)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

To evaluate the metabolic effects of dietary fiber without changing energy intake or proportions of protein, fat, and carbohydrates.

Inclusion Criteria:

Type 2 diabetes treated by diet only (e.g.: no diabetes medications)

Exclusion Criteria:

none given

Description of Study Protocol:

Recruitment

From the diabetic clinic at the health-care center in Dalby, Sweden

Design

Comparison of glycemic and lipid control in 14 subjects with type 2 diabetes controlled by diet after eight weeks of an isocaloric and controlled nutrient diet with 44 g total dietary fiber/d vs eight weeks of the same diet but with 16 g total dietary fiber/d.

Blinding used (if applicable)

Intervention (if applicable)

Subjects were randomized to either a high fiber diet (beet, legumes, or other sources) or a low fiber diet (cereal) for eight weeks, and then were crossed over to the other diet (the first two weeks of the diet served as an "adjustment" period). No fiber supplements were used. The diets were isocaloric and the portions of protein, fat, and carbohydrate were kept identical. This was an outpatient study with compliance measured and instructions given to subjects by dietitian and/or physician. Diet intakes were evaluated after 4 weeks based on patients' weekly protocols. Once a week for the 4 months of the study fasting subjects attended the health care center to measure weight and fasting blood glucose. Before, and at the end of each study period subjects ate a low-fiber test meal (2.2 g dietary fiber) and glycemic, lipidemic and hormonal measures were taken.

Statistical Analysis

Wilcoxon's signed rank test to compare differences between paired observations

Data Collection Summary:

Timing of Measurements

Baseline, 8, and 16 weeks after start of study.

Dependent Variables

Blood glucose (glucose-oxidase method)
HbA_1c (column chromatography with commercial kits)
Plasma Innumoreactive Insulin (by radioimmunoassay using Novo Kits)
Plasma C-peptide (by radioimmunoassay using Novo Kits)
Plasma glucagon (described in earlier publications by authors)
Plasma somatostatin (described in earlier publications by authors)
Plasma cholesterol (measured by conventional methods)
HDL-cholesterol (measured by conventional methods)
LDL-cholesterol (calculated: LDL = chol minus HDL minus (0.45x TG))
Triglycerides (measured by conventional methods)

Independent Variables

Dietary fiber intake (calculated from fiber values obtained by an enzymatic method) NOTE that one of the authors, Asp, developed the enzymatic method; energy and major nutrient intakes were calculated from values listed in tables from the Swedish National Food Administration).

Control Variables

Medications, such as hypertensive agents, were kept constant during the study
Body weight. If > 1 kg was gained/lost in a week or 0.5-1 kg during two sequential weeks, the caloric intake was modified to keep body weight constant.

Description of Actual Data Sample:

Initial N: 14 subjects (9 females, 5 males)

Attrition (final N): none reported, 14

Age: mean of 69.1±5.6 (SD) yrs

Ethnicity: not reported

Other relevant demographics: mean duration of diabetes, 3 yrs

Anthropometrics: average BMI: 29.2±4.4 kg/m²

Location: University of Lund, Dalby, Sweden

Summary of Results:

Variables	Baseline, mean±SD, n=14	High Fiber Diet, mean±SD, n=14	Low Fiber Diet, mean±SD, n=14	Statistical Significance (high fiber vs low fiber)
HbA_1c (%)	5.9±0.8	5.3±0.6	5.2±0.7	NS*
Fasting blood glucose (mmol/L)	6.8±1.4	6.3±1.2	6.7±1.3	p<0.01
Cholesterol (mmol/L)	5.85±0.3	5.51±0.3	5.72±0.3	p<0.025
HDL-cholesterol	0.87±0.1	0.87±0.1	0.84±0.1	NS
LDL-cholesterol (mmol/L)	4.43±0.3	4.17±0.3	4.37±0.3	p<0.025
Triglycerides (mmol/L)	1.27±0.1	1.05±0.1	1.15±0.1	NS
LDL:HDL	5.33±0.6	5.10±0.5	5.52±0.6	p<0.025

*Baseline HbA_1c significantly different from both high and low fiber diets (p<0.001)

Diet composition	Before study	High Fiber	Low Fiber
Kcal	1517±427	1545±421	1527±365
Protein (%)	19.9	24.0	22.0
Fat (%)	36.0	32.0	33.0
Carbohydrate, excluding fiber (%)	44.0	44.0	45.0
Total fiber (g)	19.5±5	43.7±10.8	15.7±4.5
Cereal fiber (g)	10.9	15.4	8.0
Beet fiber (g)	--	6.3	--
Leguminous fiber (g)	0.2	13.9	--
Other fiber (g)	8.5	8.0	7.7

Other Findings

No significant difference between baseline and either diet, and no significant difference between diets at end of eight weeks were seen for IRI, C-peptide, glucagon and somatostatin. Postprandial responses after the identical test meals at the end of each diet period indicated no significant difference between diets for the same hormones.

Author Conclusion:

Older overweight patients with type 2 diabetes who are already acceptably controlled may improve further by adopting a fiber-rich diet based on ordinary foodstuffs
The fiber-rich diet reduced the fasting blood glucose levels and improved the plasma lipoprotein profile, as evidenced by a decreasing LDL:HDL ratio.

Funding Source:

Government:

Swedish Council for Planning and Coordination of Research, Swedish Council of Forrestry and Agricultural Research, Malmohu County Council

Industry:

Forenade Liv Mutual Group Life Insurance

Other:

University/Hospital:

Univesity of Lund (Sweden)

Not-for-profit

Foundation associated with industry:

Reviewer Comments:

Potential confounding factors (e.g.: physical activity) were not controlled for.
Subjects were in good metabolic control before the start of the study. In addition, they were seen by health professionals every week (instead of the usual 3 or 6 month intervals) which could have had an effect on the further lowering of the HbA_1c during both diet periods.
This study kept the macronutrients % of energy the same for both diets, thus omitting diet confounders.

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?	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?	???
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?	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?	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?	???
	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)?	???
	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