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Citation:

Zamora D, Gordon-Larsen P, He K, Jacobs DR Jr, Shikany JM, Popkin BM. Are the 2005 Dietary Guidelines for Americans associated with reduced risk of type 2 diabetes and cardiometabolic risk factors? Twenty-year findings from the CARDIA study. Diabetes Care. 2011 May; 34(5): 1,183-1,185.

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 examine the prospective association between accordance with the 2005 Dietary Guidelines for Americans (DGA) and subsequent diabetes incidence and changes in cardiometabolic risk factors.

Inclusion Criteria:

Participants of the Coronary Artery Risk Development in Young Adults (CARDIA) study consisted of 5,115 black and white young adults recruited from 1985 to 1986 from four U.S. metropolitan areas and re-examined up to 20 years later

Exclusion Criteria:
  • Type 2 diabetes at baseline
  • Pregnancy
  • Missing data for key variables
  • Had unusually high or low daily energy intake (as per previous CARDIA research):
    • Less than 800kcal or more than 8,000kcal for men
    • Lesss than 600kcal and more than 6,000kcal for women.
Description of Study Protocol:

Study Description

  • CARDIA Study (Friedman GD, Cutter GR, Donahue RP, et al. CARDIA: study design, recruitment, and some characteristics of the examined subjects. J Clin Epidemiol. 1988; 41: 1,105–1,111)
  • Coronary Artery (Disease) Risk Development in (Young) Adults: Study participation was limited to members of the two largest racial groups in the U.S., whites and blacks
  • Participants had to be at least 18 and no more than 30 years old at the time of their initial telephone recruitment interview
  • 5,115 black and white young adults were recruited from 1985 to 1986 from four U.S. metropolitan areas and re-examined up to 20 years later.

Study Duration

20 years of follow-up.

Location

Four metropolitan areas in the United States.

Data Collection Summary:

Dietary Assessment Method

Dietary intake was assessed with the CARDIA Diet History (McDonald A, Van Horn L, Slattery M, et al. The CARDIA dietary history: Development, implementation, and evaluation. J Am Diet Assoc. 1991; 91: 1,104–1,111), an interviewer-administered instrument that includes a quantitative food frequency questionnaire.  

Dietary Index/Score Used

The 2005 Diet Quality Index (DQI) was designed to rate participants’ diets based on meeting 2005 DGA dietary recommendations. Details on the development of the 2005 DQI are published elsewhere [Zamora D, Gordon-Larsen P, Jacobs DR Jr, Popkin BM. Diet quality and weight gain among black and white young adults: the Coronary Artery Risk Development in Young Adults (CARDIA) Study (1985- 2005). Am J Clin Nutr. 2010; 92: 784–793]. The 2005 DQI, reflects the key messages conveyed by the 2005 DGA, but because there is no gold standard for measuring adherence to the DGA, the DQI 2005 Index represents its authors’ interpretation of the dietary recommendations.

Index/Score Components

Scores were based on the percentage of dietary recommendations met, specific cutoffs for nutrient intake or distribution of values in our sample. Three of the 10 DQI components include intake of key nutrients addressed by the DGA [fat (between 20% and 35% of total energy), saturated fat (10% of total energy) and cholesterol (300 mg)]. Four components quantify adequate intake of dairy (reduced fat), fruit, vegetables and grains. The last three components relate to broader health messages, including an emphasis in 2005 on consumption of a variety of foods within and among the basic food groups to achieve the recommended nutrient intakes as well as reduced intake of empty calories and sodium. Points were summed across the 10 components for a maximum score of 100, with low values reflecting a poor diet and high values reflecting a healthy diet.  

Outcomes Measured

Diabetes incidence and changes in cardiometabolic risk factors.

Methods of Outcome Assessment

Cardiometabolic outcomes were measured at exam years zero, seven, 10, 15 and 20. Type 2 diabetes was defined as fasting plasma glucose 126mg or more per dL, non-fasting glucose 200mg or more per dL, postprandial two-hour glucose 200mg or more per dL from an oral glucose tolerance test or current drug treatment for elevated glucose. Homeostasis model assessment of insulin resistance (HOMA-IR) was calculated as (fasting glucose/fasting insulin) divided by 22.5.

Description of Actual Data Sample:
  • Sample size:
    • N=5,116 in the entire cohort
    • N=4,381 in this sample.
  • Age:
    • 18 to 24 years: 44.7%
    • 25 to 30 years: 55.3%.
  • Gender: 54% female 
  • Race/ethnicity: 51% black, 49% white
  • Socioeconomic status:
    • Education:
      • 12 years or less: 39.8%
      • More than 12 years: 60.2%.
  • Baseline health status: Healthy young adults.
Summary of Results:
  • This publication focused primarily on type 2 diabetes mellitus incidence, not cardiovascular disease outcomes.There was no association between DQI score and diabetes risk using Cox models adjusted for potential confounders.
  • Participants in the highest (vs. lowest) DQI quartile had significantly less increase in blood pressure (systolic and diastolic)
  • Participants in the highest (vs. lowest) DQI quartile had greater increase in HDL cholesterol.
Confounders
Medication/ Supplement Use Physical Activity Baseline
Weight Status
Sex Age Smoking Others
  x x x x x Race, education, income, family history of type 2 diabetes mellitus, clinic (study site), HOMA-IR

 

 

Author Conclusion:

No evidence that higher accordance with the 2005 DGA was associated with lower type 2 diabetes risk. Accordance with the 2005 DGA was inversely associated with blood pressure and HDL cholesterol, but not triglycerides.

Strengths and Limitations

Potential weaknesses include factors related to the self-reported dietary data and the interval of measurement. Scoring of the DQI involves quantitative interpretation, albeit a priori and based on a validated inde.

Reviewer Comments:

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?
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?
N/A
  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)
N/A
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline?
Yes
  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?
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.)
N/A
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded?
Yes
  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?
Yes
  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?
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?
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)?
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