Increase Font Size Decrease Font Size View as PDF Print
Citation:

Liese AD, Nichols M, Sun X, D'Agostino RB Jr, Haffner SM. Adherence to the DASH Diet is inversely associated with incidence of type 2 diabetes: The insulin resistance atherosclerosis study. Diabetes Care. 2009 Aug; 32(8): 1,434-1,436.


PubMed ID: 19487638
Study Design:
Prospective Cohort Study
Class:
B - Click here for explanation of classification scheme.
POSITIVE: See Research Design and Implementation Criteria Checklist below.
Research Purpose:

To evaluate the impact of adherence to the DASH diet on risk of type 2 diabetes in the multi-ethnic Insulin Resistance Atherosclerosis Study (IRAS).

Inclusion Criteria:
  • Participants of the Insulin Resistance Atherosclerosis Study (IRAS), which recruited 1,624 participants between 1992 and 1994, aiming for equal representation across:
    • Glucose tolerance status
    • Ethnicity
    • Sex
    • Age (40 to 49, 50 to 59 and 60 to 69 years).
  • Participants who completed a one-year food frequency questionnaire at baseline.
Exclusion Criteria:

Participants with type 2 diabetes at baseline.

Description of Study Protocol:

Study Description

  • The Insulin Resistance Atherosclerosis Study (IRAS) recruited participants at four clinical centers, aiming for equal representation across glucose tolerance status (normal, impaired glucose tolerance, non–insulin-dependent type 2 diabetes), ethnicity (black, Hispanic and non-Hispanic white), sex and age (40 to 49, 50 to 59 and 60 to 69 years)
  • At baseline, habitual dietary intake was assessed and anthropometrics and glucose tolerance and insulin sensitivity were measured
  • At five-year follow-up, incidence of type 2 diabetes was determined.

Study Duration

Five years of follow-up.

Location

United States.

Data Collection Summary:

Dietary Assessment Method

One-year, semi-quantitative 114-item food frequency interview.

Brief Description of Dietary Patterns

  • The investigators created 33 food groups based on similarities in food and nutrient composition that were collapsed to create eight DASH food groups (grains, vegetables, fruits, dairy, meat, nuts/seeds/legumes, fats/oils and sweets). Adherence to the DASH diet was assessed with an index variable. The investigators additionally distinguished whole grain and low-fat dairy to address the qualitative DASH goals.
  • For each food group, a maximum score of 10 was assigned if the recommended intake was met, whereas lower intakes were scored proportionately. If lower intake were recommended, reverse scoring was applied and a score of zero was applied to intakes 200% the upper recommendation.
  • The resulting eight component scores were summed to create the overall DASH adherence score (range zero to 80).

Outcomes Measured

Incident diabetes was determined by oral glucose tolerance test results according to World Health Organization criteria or by determining which participants were taking hypoglycemic medication not previously reported at baseline.

Methods of Outcome Assessment

A 12-sample, insulin enhanced, frequently sampled intravenous glucose tolerance test was conducted and insulin sensitivity and acute insulin response were assessed using minimal model analysis. Acute insulin response was calculated based on insulin levels through the eight-minute blood samples prior to insulin infusion.

Description of Actual Data Sample:
  • Sample sizeOf 1,087 subjects with normal or impaired glucose tolerance at baseline, 906 (83%) returned to five-year follow-up, among whom 148 type 2 diabetes cases developed.
  • Age: Approximate age range 45 to 75 years
  • Gender: Both; percentages were not reported
  • Race/ethnicity:
    • Black, Hispanic and non-Hispanic white
    • Calculated 40% white and 60% Black/Hispanic.
  • Baseline distribution of dietary patternsDASH dietary pattern score range: 38.4±5.3 (tertile 1) to 60.2±4.5 (tertile 3).
Summary of Results:
  • The DASH score was associated with age, race/ethnicity, smoking, physical activity and educational attainment
  • In the total study population, the investigators initially observed a weak, inverse association of the DASH index with incident type 2 diabetes adjusting for age, sex, race/ethnicity/clinic, diabetes status, family history, education, smoking, energy intake, and expenditure. Further adjustment for BMI had little impact
  • However, upon stratification by race/ethnicity, a strong inverse association of the DASH score with type 2 diabetes was observed in whites [tertile 3 vs. tertile 1, odds ratio, 0.31 (95% CI: 0.13 to 0.75)] but not in blacks or Hispanics
  • The interaction between DASH and minority race was statistically significant (P=0.02) in the fully adjusted model
  • Adjustment for insulin sensitivity and secretion strengthened the association in the total population and in whites but had no effect in minorities
  • Adjustment for baseline glucose did not alter the findings.

Model Adjustments

  • Model 1: Adjusted for age, sex, race/ethnicity/clinic, glucose tolerance status, family history of diabetes, education, smoking status, energy intake, and energy expenditure
  • Model 2: Adjusted for covariates contained in model 1 plus baseline BMI
  • Model 3: Adjusted for covariates contained in model 2 plus baseline insulin sensitivity and secretion.
  •  
Confounders
Total Energy Intake BMI Sex Age Smoking Alcohol Intake Physical Activity
x x x x x   x

 

Author Conclusion:

Adherence to the DASH dietary pattern, which is rich in vegetables, fruit and low-fat dairy products, may have the potential to prevent type 2 diabetes.

Limitations

  • No association was observed in blacks or Hispanics possibly because of the key limitation of our study—the relatively small sample size
  • Additionally, differential accuracy of diet assessment may play a role. Therefore, replication of our study findings in a larger cohort is needed
  • Authors do not describe strengths.
Reviewer Comments:

Details of the Insulin Resistance Atherosclerosis Study (IRAS) were not included in this paper; thus, my marking of several "unclear" boxes on the rating checklist.


Research Design and Implementation 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 nutrition or dietetics practice?
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?
Yes
  2.2. Were criteria applied equally to all study groups?
Yes
  2.3. Were health, demographics, and other characteristics of subjects described?
No
  2.4. Were the subjects/patients a representative sample of the relevant population?
Yes
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 used? (Concurrent preferred over historical controls.)
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 or cross-sectional 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. Criterion may not be applicable in some cross-sectional studies.)
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?
???
  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%.)
???
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for?
???
  4.4. Were reasons for withdrawals similar across groups?
???
  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?
???
  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.)
???
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded?
???
  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?
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?
No
  6.6. Were extra or unplanned treatments described?
No
  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)?
???
  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