EAL

DF: Diabetes (2008)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

To examine the impact of dietary fibers, glycemic load and glycemic index on adiponectin concentration in women with type 2 diabetes mellitus.

Inclusion Criteria:

Female nurses, aged 30-55
Type 2 diabetes
Participating in the Nurses Health Study (NHS)
Plasma adiponectin concentrations were collected.

Exclusion Criteria:

Cardiovascular diseases at blood draw.

Description of Study Protocol:

Recruitment

902 female registered nurses, aged 30-55 enrolled in the Nurses Health Study.

Design

Cross-sectional analysis of 902 diabetic women enrolled in the Nurses' Health Study
Participants completed semi-quantitative food frequency questionnaires (FFQ)
The FFQ was administered twice to 173 nurses at an interval of approximately one year and four one-week diet records were collected for these subjects during this time period
Correlation coefficients between the FFQ and the seven-day diet records were determined for high-carbohydrate foods and foods with high and low glycemic indexes
Plasma adiponectin concentrations were measured and anthropometric data and lifestyle factors were derived from a questionnaire administered close to the date of blood collection.

Statistical Analysis

Quintiles (dietary intake values)
Linear regression modeling (dietary intake vs. plasma adiponectin)
Chi-square
Adjustment for potential confounding variables
Obesity.

Data Collection Summary:

Timing of Measurements

Semi-Quantitative Food Frequency Questionnaires: Administered once to all participants (timing not described); administered twice to 173 nurses at an interval of approximately one year (1980-1981)
Four one-week diet records collected from the 173 nurses during the approximately one-year period
Plasma adiponectin concentrations measured (timing not described)
Anthropometric data and lifestyle factors derived from 1990 questionnaire, administered closest to time of blood draw and BMI calculated
Physical activity data derived from 1988 questionnaire (self-reported and described activities over the previous year).

Dependent Variables

Variable One: Plasma adiponectin concentrations, measured by competitive radioimmunoassay with a coefficient of variation of 3.4%.

Independent Variables

Dietary fiber intake
Glycemic index
Glycemic load.

Control Variables

Age
BMI
Alcohol consumption
Physical activity
HgbA1C
HTN
Hypercholesterolemia
Post-menopausal hormone use.

Description of Actual Data Sample:

Initial N: 902 female nurses
Attrition (final N): N/A
Age: 30 to 55 years
Ethnicity: Not described in this publication
Other relevant demographics: Not described in this publication
Anthropometrics: BMI range from 26.3 to 31.9
Location: Nurses' Health Study; National.

Summary of Results:

Other Findings

Fiber type
- Intakes of cereal fiber (P=0.002) and fruit fiber (P=0.036) were significantly associated with increasing adiponectin (adjusted for potential confounders)
- Adiponectin concentrations were 24% higher in the highest (vs. lowest) quintile of cereal fiber intake
- Total fiber and vegetable fiber intakes were not associated with adiponectin concentrations (P=0.34, with BMI adjustment P=0.16).
Glycemic load and glycemic index
- Glycemic load (P=0.01) and glycemic index (P=0.03) were associated with decreasing adiponectin (with adjustment for BMI).
Obesity
- No effect of modification by obesity status on dietary fiber and adiponectin levels
- Lean individuals with the highest cereal fiber intake or lowest glycemic load had highest adiponectin concentrations
- Obese individuals with the lowest intake of cereal fibers or the highest glycemic load had the lowest adiponectin concentrations.

Author Conclusion:

Intake of cereal fiber was associated with significantly higher adiponectin concentrations in women with type 2 diabetes. Dietary glycemic load and glycemic index were inversely associated with adiponectin concentrations in this group
Obesity status did not modify the association between fiber and adiponectin and higher cereal fiber intake and lower glycemic load did not counteract the increase in adiponectin levels associated with obesity.

Funding Source:

Government:

NIH

Reviewer Comments:

Little background information on enrollment in Nurses' Health Study or demographic information for participants
Table 1 describes subjects' characteristics, according to quintiles of plasma adiponectin concentrations.

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)	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?		Yes
	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?	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?	Yes
3.	Were study groups comparable?		Yes
	3.1.	Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT)	Yes
	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?	Yes
	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?		No
	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%.)	No
	4.3.	Were all enrolled subjects/patients (in the original sample) accounted for?	???
	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?		No
	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?	No
	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?	N/A
	6.2.	In observational study, were interventions, study settings, and clinicians/provider described?	No
	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?	No
	6.5.	Were co-interventions (e.g., ancillary treatments, other therapies) described?	No
	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?	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?	No
	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)?	No
	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?	No
	8.7.	If negative findings, was a power calculation reported to address type 2 error?	No
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?	No
	10.2.	Was the study free from apparent conflict of interest?	Yes