Scientific Report of the 2020 Dietary Guidelines Advisory Committee: Methodology

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Today we're in for a doozy -- the methodology of the scientific report of the
2020 Dietary Guidelines Advisory Committee. This is the third part of our series exploring this review. If you missed the first two posts, Executive Summary and Setting the Stage and Integrating the Evidence, check those out before diving into part three: Methodology.

This one is roughly 50 pages of intense scientific scrutiny. We'll pick out the highlights, but I've also copied the exact Table of Contents below...

    • About the Topic Identification Process
    • Call for Nominations
    • Review of Nominations
    • Appointment to the Committee
    • Management of Conflicts of Interest During Committee Selection
    • Committee Meetings
    • Public Comments
    • Committee Working Structures and Processes
    • Management of Conflicts of Interest During the Committee’s Scientific Review
    • Data Analysis
      • National Health and Nutrition Examination Survey
      • National Health Interview Survey
      • Data Analysis Team
    • Food Pattern Modeling
      • Food Pattern Modeling Process
      • Food Pattern Modeling Team
    • NESR Systematic Review Process
      • Develop a Systematic Review Protocol
      • Develop an Analytic Framework
      • Search for, Screen, and Select Literature
      • Screen and Select Studies
      • Extract Data and Assess Risk of Bias 
      • Synthesize Evidence, Develop Conclusion Statements, Grade the Evidence, and Identify Research Recommendations
      • Develop Systematic Review Reports
      • Use and/or Update Existing NESR Systematic Reviews
      • NESR Team
      • Peer Review of NESR Systematic Reviews
    • Committee Report Development and Structure

This report is a summary of scientific evidence gleaned from over 270,000 articles. The committee explored systematic reviews, primary research articles, and even food pattern modeling analyses.

As mentioned in the executive summary, this was the first time that topics and questions for the committee were established before the actual committee was, in the hopes of making the process more transparent while ensuring that committee members had the proper expertise, among a host of other reasons.

The nomination process can be found on pages 5-7 of the Methodology section and was carried out according to guidelines from the Federal Advisory Committee Act. "All complete nomination packages were reviewed by program staff from USDA Food, Nutrition, and Consumer Services (FNCS), the USDA Research, Education, and Economics (REE), and the HHS Office of the Assistant Secretary for Health (OASH). Nominees were then evaluated by the USDA Acting Deputy Under Secretaries of FNCS and REE, in consultation with the HHS Assistant Secretary for Health. Each nomination package was examined using the factors listed above. For the first time, USDA and HHS also outlined specific information needed in all nomination packages, including education, employment, peer-reviewed publications, presentations, blogs, funding sources, and other affiliations."

A concern that many people have about government guidelines comes from the increasing presence of and funding for various lobbyists and special interests. The committee took extensive steps to ensure there were no concerns about "financial conflicts of interest and compliance with Federal ethics rules" in members of the committee. Further, "All meetings of the full Committee were held publicly."

The committee transitioned from in-person meetings to webinars as COVID-19 took hold in the United States. "Meeting materials, including transcripts, recordings, and presentation slides were posted at following the meetings" and public comments were very much encouraged.

To cover everything it needed to cover, the Dietary Guidelines Advisory Committee formed 6 subcommittees to address...

  • Pregnancy and Lactation
  • Birth to 24 Months
  • Dietary Patterns
  • Dietary Fats and Seafood
  • Beverages and Added Sugars
  • Frequency of Eating

There was also a "cross-cutting working group (Data Analysis and Food Pattern Modeling) that corresponded to the topics and questions specified by the Departments."

Now let's shift our focus to discuss the 3 approaches that the committee and sub-committees took when it came to examining the evidence:

  1. Data analysis
  2. Food pattern modeling
  3. The USDA’s Nutrition Evidence Systematic Review (NESR)

In terms of data analysis, "The protocol, or plan, included an analytic framework that described the overall scope and the approach used to answer the question and an analytic plan that detailed the data and subsequent analysis to be considered. The analytic results of each analysis that were used to answer a data analysis question are summarized in the report."

"Food pattern modeling is a way to evaluate the impact of specific changes in amounts or types of foods and beverages in a dietary pattern on meeting food group recommendations and nutrient needs. These food pattern modeling tests inform USDA’s development of relevant dietary patterns for the American population that reflect health-promoting patterns identified in systematic reviews and meet nutrient recommendations." These models use nutrient profiles created by a weighted average of foods in their most nutrient-dense forms. "The food group structure and corresponding nutrient profiles of the food patterns allowed the Committee to use food pattern modeling tests to see how proposed changes to food pattern elements might affect food group amounts and nutrient adequacy across the lifespan."

"Systematic reviews are research projects that answer important public health questions by evaluating scientific evidence on topics relevant to Federal policy and programs." As noted above, these reviews need the following steps in their process...

  • Developing a systematic review protocol
  • Developing an analytic framework
  • Searching for, screening, and choosing scientific literature
  • Screening and choosing studies
  • Extracting data and accurately evaluating bias risk
  • Synthesizing evidence, developing conclusion statements, grading the evidence, and identifying research recommendations
  • Creating systematic review reports
    • Plain language review summaries
    • Technical abstracts
    • Full systematic reviews
  • Using and/or updating existing NESR
  • Conducting peer reviews of NESR (this is a new step)

You can find details about any stage of this third process on pages 18-46 of the Methodology section. This committee were intensely rigorous and laser-focused on creating the best possible review of the science.

Once these reviews were concluded, the subcommittees drafted and re-drafted each chapter, discussing them in public meetings both in person and later online. "To ensure each chapter received a focused [review], 2 Committee members conducted a cross-review of each chapter." After that, "The Executive Summary was drafted by the Science Writer following her editorial review of each chapter. The Integration Chapter was drafted by the Chair and Vice Chair, with iterative review and contributions from the Integration Writing Group and review by the full Committee. Future Directions were drafted by Subcommittees to highlight research recommendations that could advance knowledge in nutrition science and inform future Federal food and nutrition guidance." The draft report was reviewed by committee members and then they held a meeting to review the whole thing in the middle of June. "The Committee then finalized the report based on member review and discussion at the meeting."

And that concludes our overview of the Methodology section. Remember, this report is not an officially-approved version of the Dietary Guidelines. It is instead "an overview of the latest available science on a variety of nutrition topics." In fact, "The 2020 Dietary Guidelines Advisory Committee was established to review scientific evidence to be considered by the U.S. Departments of Agriculture (USDA) and Health and Human Services (HHS) as the Departments develop the next edition of the Dietary Guidelines for Americans." You can read the full report here. This report is now open for public comment, and there will be an online meeting on August 11 to discuss thoughts on the initial report before it goes into the next phase of development into the official Dietary Guidelines for Americans.

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