Joint Comments to DGAC on Use of Existing Systematic Reviews

July 22, 2019

Barbara Schneeman, PhD
Chair, 2020 Dietary Guidelines Advisory Committee
c/o Eve Stoody, PhD
Designated Federal Officer
Center for Nutrition Policy and Promotion
Food and Nutrition Service
U.S. Department of Agriculture
3101 Park Center Drive, Room 1034
Alexandria, VA 22301

Dear Dr. Schneeman and Members of the 2020 Dietary Guidelines Advisory Committee:

We, the undersigned groups, are writing to request that the 2020 Dietary Guidelines Advisory Committee (DGAC) continue to make full use of existing high-quality systematic reviews and meta-analyses conducted by researchers and organizations outside of the federal government, in addition to any conducted by government researchers. We strongly agree that updates to the Dietary Guidelines for Americans should reflect the latest scientific evidence; however, we believe that a determination to explicitly exclude the use of high-quality, scientifically-sound external systematic reviews and meta-analyses will reduce the efficiency and effectiveness of the DGAC process.

Several of the proposed DGAC research questions have been recently addressed by existing high-quality reviews and meta-analyses, and these reports provide important information concerning the relevant dose-response relationships needed to support the development of these important guidelines. For example, meta-analyses on the relationship between alcohol consumption and cancer risk show that alcohol increases the risk of six different types of cancer. However, the level of consumption associated with significantly increased risk differs substantially between these cancer types. While only heavy drinking increases the risk of a number of cancers, any alcohol consumption significantly raises the risk of both breast and esophageal cancers. Because the Nutrition Evidence Systematic Review (NESR) does not conduct meta-analyses, these dose-response patterns may not be apparent if the evidence is only assessed using systematic literature reviews conducted by NESR.

We believe that a decision to exclude the use of existing high-quality systematic reviews and meta-analyses would be an unnecessary and inefficient departure from the evidence review process used by the 2015 DGAC, which utilized existing high-quality external systematic reviews, meta-analyses, or reports to answer nearly half (45%) of its research questions1. The 2015 DGAC utilized Nutrition Evidence Library (NEL; NESR’s predecessor) systematic reviews to answer only 27% of its questions. In fact, the 2017 report from the National Academies of Sciences, Engineering, and Medicine (NASEM) on the optimal process for developing the Dietary Guidelines states, "use of existing systematic reviews, meta-analyses, and authoritative reports from leading organizations is generally appropriate and encouraged by this National Academies committee, with the understanding that they ought to be relevant, timely, and of high quality."2 Although the NASEM notes, "existing systematic reviews may not use the same inclusion and exclusion criteria, may be out of date, or have different outcomes,"3 in the situations where existing systematic reviews and meta-analyses are high-quality, relevant, and timely, we strongly believe that they should be utilized.

Including existing systematic review and meta-analyses would also efficiently extend the DGAC's reach by enabling it to review a broader range of evidence. For example, four of the six relevant DGAC subcommittee protocols that have been posted as of July 1, 2019 would exclude any research published before 2000. For some questions—such as "what is the relationship between types of dietary fat consumed and risk of cardiovascular disease?"—the results of some pre-2000 randomized controlled trials are invaluable, because few recent trials have been conducted in metabolic wards or had cardiovascular endpoints. Existing meta-analyses and systematic reviews would enable the 2020 DGAC to incorporate pre-2000 evidence on a number of topics.

We acknowledge the expertise and support the methodology of the NESR team used to conduct systematic reviews. However, given the scale of the task, the finite capacity of the NESR team, and the short timeframe to address more than 80 research questions, NESR should utilize the full body of existing science and focus its time and resources most efficiently—on updates to existing high-quality systematic reviews and development of new ones on topics for which they do not already exist.

Thousands of researchers outside the federal government have devoted their careers to conducting valuable research on topics related to diet and health, including some of the specific research questions identified by the DGAC. This research, which includes systematic reviews and meta-analyses, has been peer-reviewed by the country's—and the world's—leading researchers in the field and published in the top scientific journals, at scientific conferences, and on the websites of respectable non-profit organizations. The NESR team should not unnecessarily duplicate this existing research. Just as NESR has set criteria to ensure that only timely, high-quality studies are included in its systematic reviews, criteria could also be established to ensure that only high-quality, recent systematic reviews and metaanalyses are utilized and existing reviews are updated as needed. In fact, such criteria were used by the 2015 DGAC, which conducted a quality assessment of existing reports using the Assessment of Multiple Systematic Reviews (AMSTAR) tool.4

Our organizations strongly recommend that the 2020 DGAC include external systematic reviews and meta-analyses in its evidence review process to better allow the 2020 Dietary Guidelines for Americans to be based on the best available scientific evidence. We stand ready to serve as partners to the DGAC and the federal staff and will provide details regarding specific research recommendations in our respective organizational comment letters.

Please direct any response to this letter to Deirdre McGinley-Gieser, Senior Vice President, Programs & Strategic Planning, at the American Institute for Cancer Research at

Thank you for your consideration.


American Institute for Cancer Research
1,000 Days
Academy of Nutrition and Dietetics
Advocates for better children's diets
American Academy of Pediatrics
American Cancer Society Cancer Action Network
American College of Lifestyle Medicine
American Diabetes Association
American Heart Association
American Public Health Association
American Society for Nutrition
Balanced, Inc.
Boulder County Public Health
Center for Biological Diversity
Center for Science in the Public Interest
ChangeLab Solutions
Colorectal Cancer Alliance
Consumer Federation of America
Healthy Food America
Healthy School Food Maryland
Johns Hopkins Center for a Livable Future
LiveWell Colorado
MAZON: A Jewish Response to Hunger
National Association of Pediatric Nurse Practitioners
National WIC Association
Society for Nutrition Education and Behavior
Society of State Leaders of Health and Physical Education
The Food Is Medicine Coalition
The Good Food Institute
The Open Door
True Health Initiative
Trust for America's Health
Union of Concerned Scientists
United Fresh Produce Association
Vermont Academy of Nutrition and Dietetics

1 Dietary Guidelines Advisory Committee. 2015. Scientific Report of the 2015 Dietary Guidelines Advisory Committee: Advisory Report to the Secretary of Health and Human Services and the Secretary of Agriculture. U.S. Department of Agriculture, Agricultural Research Service, Washington, DC. p. 32.

2 NASEM. Redesigning the Process for Establishing the Dietary Guidelines for Americans. Washington, DC: The National Academies Press, 2017.

3 NASEM, p. 82

4 Scientific Report of the 2015 Dietary Guidelines Advisory Committee, p. 36. Generally, articles that scored 8-11 were rated high quality and were considered by the 2015 DGAC.